THE HANDBOOK ON
SOLIDS CONTROL & WASTE MANAGEMENT 4th EDITION Published by Brandt / EPI ™
1st Edition © 1982 2nd Edition © 1985 3rd Edition © 1995 4th Edition © 1996
All rights reserved. No part of this book may be reproduced in any form without permission in writing from the publisher. Printed in the U.S.A.
PREFACE This Handbook was written by the Technical Services staff of Brandt/EPI to provide a basic understanding of effective mechanical removal of drilled solids and management of drilling wastes. Based on sound theoretical concepts, this Handbook is a practical working tool. It is designed for use by anyone needing to optimize drilling efficiency: drilling engineers, supervisors, tool pushers, mud engineers, derrick hands, service personnel and others. This 4th edition of the Handbook provides updated sections on equipment and techniques, and includes new information on waste processing systems, including downhole injection, solidification/ stabilization, water clarification, and other site remediation techniques. We would appreciate any suggestions for improving future editions of the Handbook. Please address your comments to: Brandt/EPI Technical Group P.O. Box 2327 Conroe, TX 77305 TEL: FAX:
(713) 756-4800 (713) 756-8102
Thanks, Mike Montgomery Manager, Technical Group Brandt/EPI
TABLE OF CONTENTS PAGE
DRILLING MUD AND MUD SOLIDS .....................................................1.1 1.1 1.2 1.3 1.4
BENEFITS OF SOLIDS REMOVAL BY MECHANICAL SEPARATION .....2.1 2.1 2.2
Reduced Total Solids ....................................................................................2.1 Reduced Dilution Requirements ..................................................................2.2
MECHANICAL SOLIDS CONTROL AND RELATED EQUIPMENT .........3.1 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15
Functions of Drilling Mud ............................................................................1.1 The Nature of Drilled Solids ........................................................................1.2 Properties of Drilling Mud ...........................................................................1.4 Types of Drilling Muds.................................................................................1.8
Particle Classification and Cut Point............................................................3.3 Separation by Vibratory Screening ..............................................................3.6 Shale Shakers ..............................................................................................3.14 Mud Cleaners/Conditioners........................................................................3.21 Separation by Settling and Centrifugal Force............................................3.28 Sand Trap ....................................................................................................3.29 Hydrocyclones ............................................................................................3.30 Desanders....................................................................................................3.33 Desilters.......................................................................................................3.35 Decanting Centrifuge..................................................................................3.38 Auxiliary Equipment...................................................................................3.43 Unitized Systems.........................................................................................3.48 Rig Enhanced Systems................................................................................3.49 High Efficiency Solids Removal Systems...................................................3.50 Basic Arrangement Guidelines...................................................................3.51
BRANDT/EPI™ PRODUCTS AND SERVICES ........................................4.1 Company Profile..........................................................................................................4.1 4.1 Scope of Services..........................................................................................4.1 4.2 Business Relationship...................................................................................4.1 4.3 Certification...................................................................................................4.1 4.4 Personnel Resources.....................................................................................4.2 Products and Services .................................................................................................4.2 4.5 Linear Motion Shakers..................................................................................4.3 ATL-1000 .......................................................................................................4.3 ATL-1200 .......................................................................................................4.3 LCM-2D .........................................................................................................4.4 ATL-CS...........................................................................................................4.4 LCM-2D/CM2 ................................................................................................4.5 ATL Drying Shaker........................................................................................4.5 SDW-25 Drying Shaker.................................................................................4.6 ATL-16/2 Mud Conditioner...........................................................................4.6 ATL-2800 Mud Conditioner ..........................................................................4.7 LCM-2D Mud Conditioner ............................................................................4.7 4.6 Orbital Motion Screen Separators ................................................................4.7 Tandem Screen Separator ............................................................................4.7 Standard Screen Separator ...........................................................................4.8 Mud Cleaners ................................................................................................4.8
4.10 4.11 4.12 4.13 4.14 4.15
Screen Panels................................................................................................4.9 BlueHexSM 3HX Screen Panels .....................................................................4.9 Pinnacle™ Screen Panels .............................................................................4.9 PT Screen Panels ........................................................................................4.10 Hook-Strip Screen Panels...........................................................................4.10 Hydrocyclone Units ....................................................................................4.10 Desanders....................................................................................................4.10 Desilters.......................................................................................................4.11 Centrifuges ..................................................................................................4.11 SC-1 Decanting Centrifuge .........................................................................4.11 SC-4 Decanting Centrifuge .........................................................................4.12 HS 3400 High Speed Decanting Centrifuge ..............................................4.12 SC 35HS High Speed Decanting Centrifuge..............................................4.12 HS 5200 High Speed Decanting Centrifuge ..............................................4.13 Roto-Sep Perforated Rotor Centrifuge .......................................................4.13 Dewatering Units ........................................................................................4.14 Filtration Units ............................................................................................4.14 Vacuum Degassers......................................................................................4.15 Mud Agitators..............................................................................................4.15 Portable Rig Blowers ..................................................................................4.15 Integrated Systems......................................................................................4.16 Closed Loop Processing Systems ...............................................................4.16 Coiled Tubing (CT) Processing Systems....................................................4.17 Trenchless Technology Processing Systems..............................................4.17 Live Oil Systems..........................................................................................4.17 Remediation Management Services ...........................................................4.17 Technical & Engineering Services..............................................................4.18
APPENDICES Glossary .....................................................................................................................A.2 Mud Solids Calculations Standard Calculations..................................................................................................B.1 Field Calculations to Determine Total Solids Discharge...........................................B.4 Field Calculations to Determine High and Low Gravity Solids Discharge ..............B.5 Solids Control Performance Evaluation .....................................................................B.6 Method for Comparison of Cyclone Efficiency .......................................................B.10 Mud Engineering Data Conversion Constants and Formulas..........................................................................C.1 Density of Common Materials ....................................................................................C.2 Hole Capacities ...........................................................................................................C.3 Pounds per Hour Drilled Solids — Fast Rates ..........................................................C.4 Pounds per Hour Drilled Solids — Slow Rates.........................................................C.5 Solids Content Chart ...................................................................................................C.6 Equipment Selection Pre-well Project Checklist...........................................................................................D.1 Screen Cloth Comparisons .........................................................................................D.2 Brandt/EPI Equipment Specifications........................................................................D.3 Selecting Size and Number of Agitators ....................................................................D.7 Brandt/EPI™ Sales & Service Locations ....................................................................D.8
DRILLING MUD AND MUD SOLIDS
Mud is the common name for drilling fluid. While it is outside the scope of this handbook to offer a detailed discussion of drilling fluids, a brief outline of the general characteristics of drilling mud is included to establish the basic relationships between drilling mud and solids control. Similarly, any discussion of solids control would be incomplete without establishing an understanding of the nature of mud solids — their size, shape and composition.
1.1 FUNCTIONS OF DRILLING FLUID The mud system in a drilling operation performs many important functions. Among these are: 1. Carry the drilled solids from the bottom of the hole to the surface. 2. Support the wall of the hole. 3. Control pressure within the formation being drilled. 4. Cool the bit and lubricate the drill string. 5. Clean beneath the bit. 6. Suspend cuttings while circulation is interrupted (e.g., during trips). 7. Secure accurate information from the well (cuttings samples, electric logs, etc.).
Help support the weight of the drill string. 9. Transmit hydraulic horsepower to the bit. 10. Allow removal of cuttings by the surface system. Of the ten functions listed, the following are generally considered most important: 1. Drilling mud moves the formations’ solids cut by the drill bit from the bottom of the hole to the surface. Removal of cuttings from the wellbore is essential in order to continue drilling. 2. Drilling mud must withstand the pressure exerted by the formations exposed in the hole. The pressure exerted by the mud against the formations helps the driller control the pressure created by the gas, oil and water that are exposed while drilling, thus reducing the potential for costly blowouts. 3. Drilling mud protects and supports the walls of the wellbore. The mud has a plastering effect on the walls of the hole and helps prevent the walls from caving in, causing an enlarged hole or leading to stuck pipe. 1.1
These problems significantly increase drilling expense and time. Drilling mud cools the bit and lubricates the drill string. This function is important in drilling because it increases the useful life of bits and the drill string.
Drilling mud is obviously a major factor in the success of any drilling program, and the key to any effective mud system is good solids control.
1.2 THE NATURE OF DRILLED SOLIDS Mud solids include particles that are drilled from the formation, material from the inside surface of the hole and materials that are added to control the chemical and physical properties of the mud, such as weight material. Drilled solids’ particles are created by the crushing and chipping action of rotary drill bits. Additional solids enter the well bore by sloughing from the sides of the open hole. The unit of measurement generally used to describe particle size is the micron (µ). A micron is one thousandth (0.001) of a millimeter, or approximately 0.00003973 of an inch. To relate this unit of measurement in more familiar terms, Figure 1-1 provides a list of common items and their size in microns. 1.2
ITEM Cement Dust (Portland) Talcum Powder Red Blood Corpuscles Finger Tip Sensitivity Human Sight Human Hair Cigarette (diameter) One inch
DIAMETER IN MICRONS 3-100 µ 5-50 µ 7.5 µ 20 µ 35-40 µ 30-200 µ 7520 µ 25,400 µ
Figure 1-1 Micron Size Range of Common Materials
Although individual mud solids can range in size from less than one micron to larger than a human fist, the average particle size is less than 35–40 microns, too small to be seen with the human eye. Note: The various sizes of solids particles in a particular drilling mud are referred to as the mud’s cuttings, sand, silt or clay content. This content is important to remember because solids control practices will affect the average particle size and the concentration of solids in specific size ranges which may greatly affect mud properties and drilling operations. Mud solids may be conveniently grouped according to micron size range, but unfortunately not without introducing some element of confusion. The API Committee on Standardization of Drilling Fluid Materials, in API Bulletin 13C published in 1974, recommended certain terminology for mud solids particle size in an attempt to minimize this confusion. This new terminology has not yet, however, gained universal acceptance.
The more commonly used classifications shown in Figure 1-2, cuttings, sand, silt and clay (or colloidal size) will be used throughout this handbook, as they are the most readily recognized in the field. These terms will refer to size classification only, not to material composition. CLASSIFICATION
PARTICLE SIZE (Diameter in Microns)
Larger than 500 µ
Smaller than 2 µ
Figure 1-2 Common Field Terminology of Particle Size
Note: Drilled solids can originate from sand, limestone, shale or other formations, but their classification in regard to solids control usually depends on particle size since their specific gravity is assumed to be approximately 2.6. It is important to note that commercial solids (such as barite or bentonite added for weight and viscosity) are also affected by solids control equipment, according to size. Most barite particles are in the same size group as silt (2–74 microns); bentonite particles are grouped with clay (smaller than 2 microns). From the time they enter the well until they reach the surface, drilled solids particles are continuously reduced in size by abrasion with other particles and by the grinding action of the drill pipe.
Abrasiveness of mud solids is determined by particle shape and hardness. Drilled solids come in various shapes such as round, needle shaped, platelets, cubic, etc. To be destructive, particles must be sharper and harder than the material they are to abrade. Figure 1-3 illustrates the degradation of drilled solids in a mud system. The main body of the particle becomes less abrasive with wear as the most abrasive corners continue to degrade down through the silt size to approximately 15–20 microns.
Figure 1-3 Mechanical Degradation of Drilled Solids
Particles smaller than 15–20 microns have much less abrasive effect on drilling equipment. Barite particles, which are not as hard as most drilled solids, are generally less abrasive than similarly-sized drilled solids. Other weighting materials, such as hematite, are generally harder and more abrasive than barite. Specific surface area, as it relates 1.3
to various shapes and sizes of solids, is another important concept. Specific surface area refers to the surface area per unit of weight or volume. Figure 1-4 lists examples that show surface area greatly increases per unit of mass: 1) as particle size decreases, and 2) as particles become less spherical in shape. EQUIVALENT SPHERICAL PARTICLE DIAMETER TYPE (Microns) PARTICLES
SQUARE FEET PER POUND
Figure 1-4 Effect of Particle Size and Shape on Surface Area
Surface area adsorbs or “ties-up” water. The more surface area, the more water adsorbed. As the particle size decreases toward the colloidal size, the relative effect of the water coating increases. The specific surface area has a pronounced effect on viscosity, as Figure 1-5 illustrates. The higher the relative specific surface area, the greater is the viscosity. Formations
Figure 1-5 Effect of Specific Surface Area on Viscosity
composed of clays that easily disperses into the mud produce relatively more viscosity increase and will have “wetter” separations in removal by equipment than formations that produce larger sized solids. Bentonite disperses easily into colloidal solids and also absorbs much more water than most solids types. Hence bentonite builds viscosity at relatively low concentrations. Viscosity and other mud properties are discussed in Section 1.3 of this Handbook.
1.3 PROPERTIES OF DRILLING MUD The ability of a drilling fluid to perform its functions depends on various properties of the mud, most of which are measurable and are affected by solids control.
DENSITY (MUD WEIGHT) Density is a measure of the weight of the mud in a given volume, and is frequently referred to as mud weight. The instrument used to measure density is the mud balance (see Figure 1-6). The instrument consists of a constant volume cup with a lever arm and rider calibrated to read directly the density of the fluid in lbs/gal (water = 8.33 lbs/gal) and pressure gradient in psi/1000 ft (water = 433 psi/1000 ft) or pounds per cubic foot (water = 62.4 lbs/ft).
Figure 1-6 Mud Balance
The density of the mud is related to the specific gravity of the fluid. Specific gravity is the ratio of a materials density to the density of water. Pure water has a specific gravity of 1.0. A material twice as dense as water would have a specific gravity of 2.0. A material half as dense as water would have a specific gravity of 0.5. Low gravity solids have an average specific gravity of 2.6. The solids are 2.6 times the weight of the same volume of water.
its viscosity. Viscosity is routinely measured with a Marsh Funnel and Mud Cup at the drilling site (see Figure 1-7). The person measuring the viscosity fills the funnel with a sample of mud and allows it to
VISCOSITY Viscosity measures the mud’s resistance to flow as a liquid and is one of the key physical properties of mud. Increasing the amount of solids or exposed surface area in a mud increases its resistance to flow as a liquid and therefore increases
Figure 1-7 Marsh Funnel and Cup
rotational viscometer (Figure 1-8) and is expressed in centipoise (grams per centimeter-second).
Figure 1-8 Rotational Viscometer (VG Meter)
flow through the tip of the funnel container while measuring the time in seconds that it takes to fill the mud cup to the one quart level. The funnel viscosity recorded is in seconds per quart. Internationally, funnel viscosity is recorded in seconds per thousand ccs or seconds per liter.
PLASTIC VISCOSITY A mud’s Plastic Viscosity is the portion of a mud’s flow resistance caused by the mechanical friction between the suspended particles and by the viscosity of the continuous liquid phase. In practical terms, plastic viscosity depends on the size, shape, and number of particles. For example, as the amount of drilled solids in a mud increases, the plastic viscosity also increases. Plastic viscosity is measured with a
Yield point is the part of flow resistance that measures the positive and negative inter-particle, or attractive, forces within a mud. Yield point is measured with a viscometer and expressed in lbs/100 ft 2. Internationally, yield point is sometimes measured in dynes/cm2.
GEL STRENGTH Gel Str ength is a function of a mud’s inter particle forces and gives an indication of the amount of gelation that will occur after circulation ceases and the mud remains static for a period of time. Typically, gel strengths are reported for initial and 10-second gel strength. A large deviation of these two figures may indicate progressive gels, that is, gelation structures that gain strength over time. Gel strength is also measured with a viscometer and expressed in lbs/100 ft 2 . Internationally, gel strength is sometimes measured in dynes/cm2.
SOLIDS CONTENT The solids content is the volume percentage of the total solids in the
Figure 1-9 Retort (Mud Still)
mud. To determine the solids content of a mud containing weight material, a mud container in the retort is filled with a measured volume of mud (see Figure 1-9). The mud is then heated to boil off the liquid. The percentage of the liquid distilled off is measured in a glass cylinder and subtracted from 100%. The difference is the percentage of solids by volume contained in the drilling mud and is recorded as percentage solids. The total solids from the retort and mud weight are used to calculate the low and high gravity solids content. If the mud does not contain oil or weight material, such as barite or hematite, the low gravity solids can be determined without a retort by weighing the mud and referring to a solids content chart.
SAND Sand is any particle larger than 74
microns when referring to solids control separation. Therefore, the sand content of a mud is simply the amount of solids too large to pass through a US Test Sieve 200-mesh screen. This is determined with a sand content set (see Figure 1-10) by washing a measured amount of mud through the 200-mesh screen in the kit. The amount of solids that does not pass through the screen is measured as percentage by volume and is recorded as perFigure 1-10 cent sand. Sand Content Set
FILTRATION Filtration and wall-cake building are actions that the drilling mud carries out through and on the walls of the hole. Some formations allow the liquid in the mud to seep into them, leaving a layer of mud solids on the wall of the hole. This layer of mud solids is called filter cake or wall-cake. The filter cake builds up a barrier and reduces the amount of the liquid that enters the formation and is lost from the mud. This process is referred to as filtration, or fluid loss. The instrument used to measure the fluid loss due to filtration is a filter press (see Figure 1-11). 1.7
Figure 1-11 Filter Press
The person using the filter press places a mud sample in the instrument on top of a piece of filter paper and brings the pressure up to 100 pounds per square inch. The amount of fluid flowing from the sample in 30 minutes is measured in milliliters. The mud filtration property is recorded in units of cubic centimeters (ccs) or milliliters (ml) per 30 minutes. Examination of the filter paper will indicate how the solids will plaster the wall of the hole and affect fluid loss. The cake thickness is recorded in units of 1/32s of an inch.
CHEMICAL PROPERTIES Chemical Properties is a broad category, including measurements of pH, alkalinity, chlorides, calcium 1.8
content, salt content, and other properties that affect drilling mud performance. Some of these chemical properties can be controlled through various mud additives that thicken, thin, precipitate, disperse, emulsify, lubricate or otherwise adjust the mud depending on specific drilling needs. For example, caustic soda can be added to some saltwater mud in order to maintain a high pH level; it makes dispersants more effective and reduces corrosion. Chemical changes such as these are used to fine tune drilling muds.
1.4 TYPES OF DRILLING MUDS Drilling fluids are generally categorized as “water-base” or “oilbase”, and as “weighted” or “unweighted” muds. Water-base Muds contain water as the liquid phase and are used to drill most of the wells in the world because they are relatively simple, expense is usually reasonable, and water is commonly available in most places. Oil-base Mud contains either natural oil or synthetic oil as the continuous liquid phase and is used for maximum hole protection. Oilbase mud and synthetic oil mud are usually much more expensive than water-base mud and therefore are only used when there is a specific
need, such as to keep the hole from swelling or caving in, or to reduce friction and prevent stuck pipe in very crooked or high angle holes. Either water-base or oil-base mud can be used as “weighted” mud. Weighted Mud refers to any mud which has barite or barite substitutes added to increase density. These muds normally have a density greater than 10.0 lbs/gal. The solids in weighted mud consist of drilled solids from the hole, plus barite, plus commercial clays added to control fluid loss and viscosity. Unweighted Mud refers to any mud which has not had barite added. This mud type normally has a density of less than 10.0 lbs/gal. The solids in unweighted mud consist of drilled solids from the hole, plus commercial clays. Solids control techniques will vary considerably depending on the type of mud being used. For example, with many unweighted water-base muds, the loss of fluids along with the drilled solids may be economically insignificant, allowing simple solids control techniques. In the case of mud that contains expensive chemical additives and/or barite, especially oil-base mud, sophisticated solids control techniques must be utilized to minimize overall costs. In addition, environmental costs of haul-off and
disposal may require sophisticated solids control techniques. System recommendations for specific applications are covered in detail in Chapter 4. Here is a list of the most common mud types, followed by a brief description of each type: I. Water-Base Mud (WBM) A. Spud Mud B. Natural mud C. Chemically-Treated Mud 1. 2. 3. 4. 5.
Lightly Treated Chemical Mud Highly Treated Chemical Mud Low Solids Mud Polymer Mud Calcium Treated Mud
Saltwater Mud 1. 2.
Sea Water Mud Saturated Salt Mud
II. Oil-Base Mud (OBM) A. “True” Oil Base B. Invert Emulsion C. Synthetic (SBM)
SPUD MUD Spud Mud is used to start the drilling of a well and continues to be used while drilling the first few hundred feet of hole. Spud mud is usually an unweighted water-base mud, made up of water and natural solids from the formation being drilled. It may contain some commercial clay, added to increase viscosity and improve wall-cake building properties. 1.9
NATURAL MUD Natural Mud (sometimes called “native” mud) is usually unweighted water-base mud which contains mostly drilled solids. Some bentonite and small amounts of chemicals may be used to improve filter cake quality and help prevent hole problems. This mud is often the next mud type used after spud mud. Often, natural mud is used to drill the first few thousand feet of hole, where only minor hole problems are expected.
CHEMICALLY TREATED MUD Chemically Treated Mud is waterbase mud which contains chemicals to control physical and chemical properties. Bentonite is usually added to help control viscosity and fluid loss. Barite (weight material) may be added to increase density. This mud is used where more severe hole problems are expected, in order to prevent these problems. Lightly Treated Chemical Mud is usually unweighted water-base mud. It is used where minor hole problems are expected, such as sloughing or caving of the walls of the hole. Highly Treated Chemical Mud is usually weighted, water-base mud that contains larger amounts of chemicals, bentonite, additives, and barite to maintain strict control of viscosity, fluid loss, chemical prop1.10
erties, and density. Chemical muds are often treated with lignosulfonates or lignite and are therefore commonly called “lignosulfonate mud” or “lignite” mud. These muds are used where moderate to severe hole problems are expected or high down-hole pressures occur. Of all the water-base mud types, these are the most expensive to maintain. As mud density is increased and potential hole problems (such as stuck drill pipe) become more of a risk, the removal of drilled solids by mechanical solids control equipment becomes increasingly important. Low Solids Muds are water-base mud containing less than ten percent (10%) drilled solids; 1–5% is a normal range. Generally speaking, the lower the solids content in the mud, the faster the bit will drill. Low solids muds are usually expensive to maintain because the solids, chemical, and fluid loss properties have to be kept very close to prescribed levels. It is absolutely essential that all solids removal equipment operate at maximum effectiveness in order to maintain the desired low level of solids at a reasonable cost. Polymer Muds are special types of low solids mud which contain synthetic materials, polymers, designed to control viscosity and fluid loss. Polymers are very expensive and
often difficult to screen when a high viscosity fluid is used. Calcium Treated Muds are special water-base muds, usually weighted, which have lime or gypsum added. Calcium Treated Muds are normally used to prevent shale type formations from swelling or sloughing – problems which could lead to stuck pipe or a ruined hole.
SALTWATER MUD Saltwater Muds contain a high concentration of salt. They may be weighted or unweighted. Sea Water Muds contain sea water as the continuous phase and, usually, only sea water is used for dilution. They may be weighted or unweighted. These muds are used offshore and in bay areas where fresh water is not readily available. When sea water mud is being used, only sea water should be used to rinse or wash the screens in solids control equipment. Saturated Salt Muds (sometimes called brine fluids) contain as much salt as can be dissolved in the water phase. This mud type is often used to drill through salt formations so the fluid will not dissolve the salt formation. If fresh water mud is used, greatly enlarged holes would result, usually leading to hole trouble. It is important to be aware of the use of salt mud because screen
blinding can occur when salt dries and cakes on the solids control equipment. Fresh water may be used to clean the screens, but it must be used very carefully because too much fresh water can upset the chemical balance of this mud.
“TRUE” OIL-BASE MUD “True” Oil-base Mud contains a liquid phase with ninety to ninetyfive percent (90–95%) diesel oil and five to ten percent (5–10%) water emulsified within the oil. These muds often use asphaltic type materials suspended in the liquid for controlling viscosity and fluid loss. “True” oil-base muds provide good hole protection, especially in shale type formations, and also increase drill string lubrication.
INVERT EMULSION MUD Invert Emulsion Mud is oil-base mud in which the liquid phase is sixty to ninety percent (60–90%) diesel oil with ten to forty percent (10–40%) water emulsified within the oil. An invert mud can be formulated with mineral oil or other low environmental risk oil substitutes when needed. In this mud, water and chemicals are used together to control viscosity and fluid loss. Invert emulsion muds provide good hole protection and are the most commonly used oil mud. 1.11
SYNTHETIC OIL MUDS The term “Synthetic-Based Mud”, or SBM, describes any oil-base mud that has a synthesized liquid base. Some common synthetic base fluids include linear alphaolefins (LAO), straight internal olefins (IO), polyalphaolefins (PAO), vegetable oils, esters, and ethers. This base fluid is then combined with viscosifiers, weighting material, and other additives to produce a stable, useful drilling fluid. SBMs share several advantages with traditional oil-base muds, including excellent wellbore stability, improved drilling rates, good hole cleaning, excellent cuttings integrity, and reduced torque. SBMs also provide additional health and safety benefits — higher flash points, lower vapor production, and
reduced eye and respiratory irritation. The major benefit of SBMs over traditional OBMs is the reduced environmental impact of cuttings and liquid mud. Currently, SBMs and cuttings meet U.S. offshore environmental requirements and may be discharged under WBM protocols. SBMs are expensive, $200–400 /bbl., depending on the oil/water ratio. Proper solids removal and liquid recovery techniques must be used to maintain desired fluid properties and drilling rate, and to control mud maintenance costs. The alternatives to mechanical solids control — dilution and whole SBM additions — are prohibitively expensive when compared to the cost of proper solids control equipment.
BENEFITS OF SOLIDS REMOVAL BY MECHANICAL SEPARATION
INTRODUCTION Of all the problems that could conceivably occur during the drilling of a well, mud contamination from drilled solids is a certainty. The volume and type of solids present in drilling mud exert a considerable influence over mud treating costs, drilling rates, hydraulics, and the possibility of differential sticking, kicks, and lost returns. Solids control is one of the most important phases of mud control — it is a constant issue, every day, on every well. If drilled solids can be removed mechanically, it is almost always less expensive than trying to combat them with chemicals and dilution. The primary reason for using mechanical solids control equipment is to remove unwanted drilled solids particles from the mud in order to prevent drilling problems and reduce mud and waste costs, thereby reducing overall drilling costs. The benefits of solids removal by mechanical separation can best be seen in terms of two outcomes: 1) reduced total mud solids and 2) reduced dilution requirements.
2.1 REDUCED TOTAL SOLIDS The presence of large amounts of drilled solids in a drilling mud usually spells trouble for the drilling operation. These solids adversely affect the performance characteristics of the mud and can lead to a multitude of costly hole problems. Drilled solids decrease the life of a mud pump’s parts and thus, can decrease drilling efficiency due to lost time for pump repairs. Continued recirculation of drilled solids produces serious mud problems because recirculated solids will gradually be reduced in size. The smaller the solids become, the more they negatively influence mud properties and hydraulic performance. The greatest impact of the solids is seen in reduced ROP. The higher the drilled solids content, the lower the penetration rate. If mud solids are not properly controlled, the mud’s density can increase above its desired weight and the mud can get so thick that it becomes extremely difficult or even impossible to pump. Since the earliest days of the oilfield, drillers have been trying to combat high solids content through the use of settling pits. However, 2.1
some drilled solids are so finely ground that they tend to remain in suspension. This results in increased mud viscosity and gel strength which, in turn results in larger particles also remaining in suspension. Thus, the approach of removing cuttings through settling alone is of limited practical value. Solids control equipment was developed in order to more effectively remove unwanted solids from drilling mud. A variety of devices (which will be discussed in detail in Chapter 3 of this handbook) are available which mechanically separate the solids particles from the liquid phase of the mud. Thus the driller, depending on the particular situation and equipment used, can regulate to a fine degree the amount and size of solids particles that are removed or maintained in any given drilling mud. Such control of mud solids through mechanical separation allows the mud to perform its drilling-related functions and avoids the downhole problems caused by excessive solids contamination. Effective solids control permits viscosity and density to be kept within desired levels, dramatically increases the life of pump parts and drill bits, and promotes faster penetration — all of which decrease the time and expense of drilling. 2.2
2.2 REDUCED DILUTION REQUIREMENTS A common method of trying to offset the build-up of drilled solids is the addition of more liquid. This is known as dilution and does not remove cuttings but reduces (or dilutes) their concentration in a drilling mud, thereby reducing the percent of total solids in the mud. However, it is important to note that dilution is expensive. Every barrel of dilution water (or oil) added requires an additional amount of chemicals, barite or other materials in order to maintain desired mud properties. The lower the drilled solids content to be maintained, the greater the dilution required. In the case of an oil-base mud, oil must be used for dilution — which can become extremely expensive. It should be noted that chemical treatment alone will ultimately result in high solids content and uncontrollable mud properties. The most effective approach is to use mechanical solids control equipment to remove as much of the drilled solids as possible before they are incorporated into the mud system and then treat what is left with appropriate amounts of chemicals and dilution. Effective solids removal by mechanical separation can maintain a minimum solids level in drilling
mud and greatly reduce the need for dilution. Reducing the need to dilute the mud can drastically decrease the cost of having to purchase mud products such as weight material (barite) and chemicals. These materials are expensive — mud costs can be 10% of the total cost of drilling a well. The Dilution Ratio Chart (Figure 2-1) can be used indirectly to approximate the amount of dilution that can be eliminated by use of solids removal equipment. For example, suppose a drilling engineer required that no more than 5% solids were to be maintained in an unweighted mud. The chart shows that at 5%, each barrel of mud would contain about 45 pounds of drilled solids. If solids control equipment were removing 1 ton (2000 lbs) of solids per hour, then the equipment would save 2000 ÷ MUD WEIGHT (LBS/GAL) TO BE MAINTAINED
DRILLED SOLIDS PERCENT BY VOLUME
8.5 8.6 8.7 8.8 8.9 9.0 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 10.0
1.2 2.0 2.7 3.5 4.2 5.0 5.7 6.4 7.2 8.0 8.7 9.4 10.2 11.0 11.7 12.4
45 = 44 barrels of dilution per hour. If the chemicals and additives were worth only $10 per barrel, the mud treating costs would be reduced by approximately $440 per hour! Over the life of a drilling operation, $440 per hour adds up to a very significant cost savings. The same procedure can be used to show reduced dilution requirement in weighted mud. When heavily — weighted muds (16–18 lbs/gal) are being used, drilling usually proceeds more slowly and less drilled solids are removed per hour. However, if approximately 5% drilled solids are allowed in the mud, then each barrel of mud still contains roughly 44 pounds of drilled solids. Therefore, if the solids control equipment were removing even a pencil-sized stream of solids which would amount to 44 pounds per POUNDS OF 2.6 SPECIFIC GRAVITY SOLIDS PER BARREL OF MUD 11 18 25 32 38 45 52 59 66 73 79 86 93 100 107 114
BBLS OF WATER REQUIRED TO DILUTE 1 TON SOLIDS AND MAINTAIN MUD WEIGHT 182 111 80 63 53 44 38 34 30 27 25 23 22 20 19 18
Figure 2-1 Dilution Ratio Chart
hour, then 44 ÷ 44 = 1 barrel of dilution saved per hour. With the high cost weighted mud (usually a minimum of $30 per barrel), the solids removal equipment would be saving at least $30 per hour. Over an average operation of 20 hours per day, this represents a savings of approximately $600 per day. If the maximum amount of drilled solids were reduced to 3%, the cost savings would double to approximately $1200 per day. The expense of the dilution liquid is a major factor in considering the advantages of reduced dilution requirements. Oil is obviously much more costly than water, but water also can be expensive if it has to be trucked into a remote drilling location. The disposal of “waste” mud can also be a significant factor in overall dilution costs. Heavy reliance on dilution to control solids content can result in the addition of so much extra liquid that the volume of mud exceeds the capacity of the active mud pits. When this happens, whole mud (including all of the expensive additives) must be discarded into waste or reserve pits. Appropriate use of solids control equipment in place of dilution lessens the volume of the mud system and can usually eliminate the 2.4
discarding of excess mud. The size of the active and waste pits themselves can be reduced due to smaller capacity requirements. Instead of throwing away valuable mud additives, these can be salvaged and returned to the active mud system. If properly used, solids control equipment can virtually eliminate waste liquid mud through a “closed mud system”. In such a system the liquid phase can be recycled — which can be critical in special applications such as when using oil-base or polymer muds, especially offshore, or where environmental concerns prohibit disposal of liquid waste materials. In these cases the cost of hauling the liquid waste away for disposal is also avoided. Solids removal by mechanical separation can achieve the benefits of low solids content and at the same time significantly reduce the many costs associated with dilution.
MECHANICAL SOLIDS CONTROL AND RELATED EQUIPMENT
INTRODUCTION The goal of modern solids control systems is to reduce overall well costs by prompt, efficient removal of drilled solids while minimizing the loss of liquids. Since the size of drilled solids varies greatly — from cuttings larger than one inch in diameter to sub-micron size — several types of equipment may be used depending upon the specific situation. The fundamental purpose for solids removal equipment is just that — remove drilled solids. The end result is reduced mud and waste disposal costs. To reach this goal, each piece of equipment will remove a portion of the solids, either by screening or centrifugal force. Each type of equipment is designed to economically separate particles of a particular size range from the liquid. Also to operate effectively, each type of equipment must be sized, installed, operated, and maintained properly. The efficiency of the solids control system can be evaluated by comparing the final volume of mud accumulated while using the equipment to the volume of mud that would result if drilled solids were controlled only by dilution. The
overall results of solids removal can be monitored by the use of flow meters to determine the actual mud volume built. The efficiency of solids removal equipment and/or systems used can be evaluated in two ways: 1) Efficiency of drilled solids removal, 2) Efficiency of liquid conservation. The greater percentage of drilled solids removed, the higher the removal efficiency. The higher the solids fraction of the waste stream, the better. Both aspects should be considered. For example, a desilter usually does well at removing solids but at the cost of significant losses of liquid; sometimes 80% of the volume of the waste stream will be liquid. By contrast, a properly operating shale shaker or centrifuge typically removes 1 barrel or less of mud with each barrel of solids. Most remaining equipment delivers a lesser degree of dryness than do the shakers or centrifuges. Most solids control systems include several pieces of equipment connected in series. Each stage of processing is partly dependent upon the previous equipment functioning correctly so as to allow the next stage to perform its role. 3.1
Should one piece of equipment fail, the equipment downstream will soon lose efficiency or fail completely. The first piece of equipment used to separate the solids from the mud is usually a vibrating screen or series of screens. The cuttings that are larger than the mesh openings are removed by the screen but carry an adhered film of mud. The screen mesh should be sized to prevent excessive losses of whole mud over the end screen. The second step is to remove the sand-sized, silt sized and larger clay particles that were not removed in the shakers by using hydrocyclones. Hydrocyclones with a cone diameter of 6 to 12 inches are called desanders, and hydrocyclones with a cone diameter of less than 6 inches are called desilters. These units should normally be sized to process 125% of the maximum flow rate used to drill. Sometimes a screen is used below a hydrocyclone to “dry-out” the
cone’s discharge to minimize the loss of fluid. The hydrocyclone and vibrating screen device is called a mud cleaner or mud conditioner. If a location must be “pitless”, then the screens are essential to minimize the liquid waste volume. The final step may be to remove the ultrafine silt and clay-sized solids with the use of a decanting centrifuge. On a weighted mud, two centrifuges may be used in series: the first to salvage barite, the second to remove fine solids and reclaim the valuable liquid phase.
3.1 PARTICLE SIZE AND CUT POINT Modern drilling rigs may be equipped with many different types of mechanical solids removal devices depending on the application and requirements of a particular project. Each device has a specific function in the solids control process. Equipment commonly utilized and the effective removal range for each are listed in Figure 3-1.
Figure 3-1 Particle Diameter and Ideal Equipment Placement
CUT POINT Notice the removal range, or Cut Point, is given as a range of the particle size removed. Mechanical solids control equipment classifies particles based on size, shape, and density. It is typical to refer to particles as being either larger than the cut point of a device (oversize) or
smaller than the cut point (undersize). Figure 3-2 shows a typical cut point curve. The cut point curve represents the amount of solids of a given size that will be classified as either oversize or undersize. Particles to the right of the cut point curve, in the area labeled “A”, rep3.3
Figure 3-2 Typical Cut Point Curve
resent the removed, oversize solids. Particles to the left of the curve, in the area labeled “B”, represent the undersize solids returned with the whole mud. Particular interest is given to three points along the cut point curve, the D50, the D16, and the D84. Given these three points, the removal characteristics of screens, hydrocyclones, or other devices can be compared. The D50, or median cut point, is the point where 50% of a certain size of solids in the feed stream will be classified as oversize and 50% as undersize. The D16 and D84 are the
points where 16% and 84%, respectively, of the solids in the feed stream will be classified as oversize. These two points are statistically significant because they are one standard deviation from the D50 in a normal distribution. An “ideal” classifier (the dashed line) would show very little difference between the D50, D16 and D84. Separation Efficiency is a measure of the D50 size relative to the number of undersize particles that are removed or oversize particles that are not removed. The higher the separation efficiency, the lower the
Figure 3-3 Separation Curve
false classification. An example will assist in understanding this concept. Figure 3-3 shows the cut point curves for two screens, each with the same D50. Curve No.1 is almost vertical with a small tail at each end. This results in a very sharp, distinct cut point. Almost all particles larger than the cut point are rejected, with very few undersize solids. Almost all particles smaller than the cut point are recovered, with very few oversize particles included. Curve No. 2 is an S-shaped curve with a large tail at each end. Even though the D50 is the same as for Curve No.1, the D16 and D84 are very
different. Many solids larger than the D50 are returned with the undersize solids and many solids smaller than the D50 are discarded with the oversize solids. If curves number 1 and 2 in Figure 3-3 illustrate typical removal gradients for two different types of oilfield shale shakers screens, we can draw conclusions about separation performance. The area between the curves marked “A” represents solids Screen No.1 removes and Screen No. 2 returns. Likewise, the area marked “B” represents solids recovered by Screen No.1, but discarded by Screen No. 2. This is not to say that Screen No.1 3.5
is “better” than Screen No. 2, or vice versa; it simply illustrates that two devices with similar “cut point” (as measured by the D50 alone) may perform very differently. As an example, consider solids removal from a weighted drilling fluid using vibrating screens. An effective solids control program for weighted mud should remove as many undesirable, sandsized solids as practical, while retaining most of the desirable, siltsized barite particles. Referring back to Figure 3-3, Screen No. 2 would return all the sand in area “A” that Screen No.1 would catch, and Screen No. 2 would remove the siltsize material in area “B” (including all weighting material) that Screen No.1 would recover. Therefore, in a weighted mud, Screen No. 2 would not perform as well as Screen No.1. Further, if the area to the right of both curves (representing total mass solids removal) were calculated, Screen No.1 could prove superior in terms of mass solids removal. As shown by this example, it is important to view “cut point” as a continuous curve, rather than a single point. This concept is equally true with screens, hydrocyclones, centrifuges, or any other separation equipment — the relative slope and shape of the cut point curve are more important than a single point on the curve. 3.6
3.2 SEPARATION BY SCREENING One method of removing solids from drilling mud is to pass the mud onto the surface of a vibrating screen. Particles smaller than the openings in the screen pass through the holes of the screen along with the liquid phase of the mud. Particles too large to pass through the screen are thereby separated from the mud for disposal. Basically, a screen acts as a “go–no go” gauge: Either a particle is small enough to pass through the screen opening or it is not. The purpose of vibrating the screen in solids control equipment is to transport the cuttings off the screen and increase the liquid handling capacity of the screen. This vibrating action causes rapid separation of whole mud from the oversized solids, reducing the amount of mud lost with the solids. For maximum efficiency, the solids on the screen surface must travel in a predetermined pattern — spiral, elliptical, orbital or linear motion — in order to increase particle separation efficiency and reduce blockage of the screen openings. The combined effect of the vibration and the screen surfaces result in the separation and removal of oversized particles from drilling mud.
SCREENING SURFACES Screening surfaces used in solids control equipment are generally made of woven wire screen cloth, in many different sizes and shapes. The following characteristics of screen cloth are important in solids control applications. Screens may be constructed with one or more Layers. Non-layered screens have a single layer, finemesh, screen cloth (reinforced by coarser backing cloth) mounted on a screen panel. These screens will have openings that are regular in size and shape. Layered screens have two or more fine mesh screen cloths, usually of different mesh (reinforced by coarser backing cloth), mounted on a screen panel. These screens will have openings that vary greatly in size and shape. To increase screen life, especially in the 120–200 mesh range, manufacturers have incorporated two design changes: 1) A coarse backing screen to support fine meshes, and 2) Pre-tensioned screen panels. The most important advance has been the development of pretensioned screen panels. Similar panels have been used on mud cleaners since their introduction, but earlier shakers did not possess the engineering design to allow their use successfully. With the advent of modern, linear-motion shakers, pre-
tensioned screen panels have extended screen life and justified the use of 200-mesh screens at the flowline. The panels consist of a fine screen layer and a coarse backing cloth layer bonded to a support grid (Figure 3-4). The screen cloths are pulled tight, or tensioned, in both directions during the fabrication process for proper tension on every screen. The pre-tensioned panel is then held in place in the bed of the shaker.
Figure 3-4 Pretensioned Screen
Today, fine screens may be reinforced with one or more coarse backing screens. The cloth may also be bonded to a thin, perforated metal sheet. This extra backing protects the fine screen from being damaged and provides additional support for heavy solids loads. The screens equipped with a perforated plate may be available with several sizes options for the perforation to allow improved performance for a given situation. Most manufacturers limit themselves to one support grid opening 3.7
size to reduce inventory and production costs. The opening size is typically 1” for maximum mechanical support. Brandt / EPI™ provides screen panels with a variety of openings to allow rig personnel to choose the desired mechanical support and total open area (translating to more liquid flow), depending on the application. Mesh is defined as the number of openings per linear inch. Mesh can be measured by starting at the center of one wire and counting the number of openings to a point one inch away. Figure 3-5 shows a sample 8 mesh screen. A screen counter is useful in determining screen mesh (see Figure 3-6).
SCREEN CLOTH There are several types of wire cloth used in the manufacture of oilfield screens. The most common of these are Market Grade and
Figure 3-5 Eight Mesh Screen
Tensile Bolting Cloth. Both of these are square mesh weaves, differing in the diameter of wire used in their construction. Market grade cloths use larger diameter wires and are more resistant to abrasion and premature wear. Tensile bolting cloths use smaller diameter wire and have a higher Conductance. Since screen
Figure 3-6 Screen counter and Magnified View of Screen mesh
Figure 3-7 One-half Inch Opening
selection is a compromise between screen life, liquid capacity, and particle separation, both types are in wide use.
OPENING SIZE Size of Opening is the distance between wires in the screen cloth and is usually measured in fractions of an inch or microns. Figure 3-7 shows a screen with a 1/2 inch opening. Screens of the same mesh may have different sized openings depending on the diameter of the wire used to weave the screen cloth. Smaller diameter wire results
4 Mesh: .080 Wire 46.2% Open Area
in larger screen openings, with larger particles passing through the screen. The larger the diameter of the wire, the smaller the particles that will pass through the screen. Remember, it’s the size of the openings in a screen, not the mesh count, that determines the size of the particles separated by the screen. Also, normally the larger the diameter of the wire used in the weaving process, the longer the screen cloth will last.
PERCENT OPEN AREA Percent Open Area is the amount of the screen surface which is not blocked by wire. The greater the wire diameter of a given mesh screen, the less open space between the wires. For example, a 4 mesh screen made of thin wire has a greater percent of open area than a 4 mesh screen made of thick wire (see Figure 3-8). The higher the percent of open area of a screen the greater its theoretical throughput. Open area can
4 Mesh: .072 Wire 50.7% Open Area
4 Mesh: .063 Wire 56.0% Open Area
Figure 3-8 Percent of Open Area
be increased for a given mesh by using smaller diameter wire, but at the sacrifice of screen life. The choice of any particular screen cloth therefore involves a compromise between throughput and screen life. Calculating the percent open area for layered screens is difficult and inaccurate. This is due to the random and wide variety of openings present. Conductance of a screen is an experimental measure of the flow capacity of a screen. The higher the conductance of a screen, the greater its flow capacity.
SHAPE OF OPENING Shape of Opening is determined by the screen’s construction. Screens with the same number of horizontal and vertical wires per inch produce square-shaped openings and are referred to as Square Mesh screens. Screens with a different number of horizontal and vertical wires per inch produce SQUARE MESH
oblong — or rectangular — shaped openings and are referred to as Rectangular (or Oblong) Mesh screens. This is illustrated in Figure 3-9. Use of a single number in reference to a screen usually implies square mesh. For example, “20 mesh” usually identifies a screen with 20 openings per inch in either direction. Oblong mesh screens are generally labeled with two numbers. For example, a 60 x 20 screen has 60 openings per inch in one direction and 20 openings per inch in the other direction. It has become common industrial practice to add the two dimensions of an oblong mesh screen and refer to the sum of the two numbers as the mesh of the screen. For example, a 60 x 20 mesh screen is often called an “oblong 80” mesh. This screen has oblong openings measuring 1040 x 193 microns, much larger than the OBLONG MESH
Figure 3-9 Shape of Opening
OBLONG MESH SQUARE MESH B-20 B-40 B-60 B-80 B-100 B-120
S-16 S-30 S-40 S-50 S-60 S-80
Figure 3-10 Equivalent Screen Sizes
square openings of a “square 80” mesh screen (177 x 177 microns). The “oblong 80” will allow much larger, irregularly-shaped particles to pass through its openings than the 80 x 80 square mesh screen.
EQUIVALENT SCREEN MESH Screen manufacturers now compare different types of screen through charts, such as the one shown in Figure 3-10. The oblongmesh screens listed in the left-hand column remove similar sized solids as the square-mesh screens listed in the right-hand column. These screens are referred to as “equivalent”. In actual field use, the conductance and screen life of the oblong mesh screens is noticeably higher than the equivalent square mesh screen, but the shape of the cut point curve discussed earlier is not as sharp or distinct. In a similar fashion, a layered screen will often be designated by a single number, e.g. “layered 210” mesh. This implies a screen with
openings smaller than a “square 200” mesh screen (74 x 74 microns). However, the actual opening size and shape of a layered screen is a combination of the multiple screen layers and will produce a wide variety of opening sizes and shapes. Therefore, the “layered 210” mesh screen will remove some solids smaller than 74 microns, but will also allow some particles larger than 74 microns to pass through the screen openings.
SCREEN PLUGGING AND BLINDING Screen Plugging and Blinding, while present to some degree on rig shakers fitted with coarser screens, is most frequently encountered on fine screen shakers. If the mesh openings plug with near-size particles or if the openings become coated over, the throughput capacity of the screen can be drastically reduced and flooding of the screen may occur. Plugging can often be controlled by adjusting the vibratory motion or deck angle, but sometimes requires changing screens to a coarser or finer mesh. A coarser screen should be used only as a temporary solution until the particular formation responsible for near-size particle generation is passed. Changing to a finer mesh screen often presents a better, more permanent solution. Screen blinding is caused by 3.11
sticky particles in viscous mud coating over the screen openings or by the evaporation of water from dissolved solids or from grease and requires a screen wash-down to cure. This wash-down may simply be a high pressure water wash, a solvent (in the case of grease, pipe dope or asphalt blinding), or a mild acid soak (in the case of blinding caused by hard water). Stiff brushes should not be used to clean fine screens because of the fragile nature of fine mesh screen cloth. Screen life of fine mesh screens varies widely from design to design, even under the best of conditions, because of differences in operating characteristics. Screen life can be maximized by following these general precautions: • Keep screens clean. • Handle screen carefully when installing. • Keep screens properly tensioned. • Do not overload screens. • Do not operate shakers dry.
Drilling rate affects screen capacity because increases in drilled solids loading reduce the effective screen area available for mud throughput. The mesh of the screen in use is also directly related to shaker capacity because, in general (but not always), the finer a screen’s mesh, the lower its throughput. Increased viscosity, usually associated with an increase in percent solids by volume and/or increase in mud weight, has a markedly adverse effect on screen capacity. As a general rule, for every 10% increase in viscosity, there is a 2–5% decrease in throughput capacity. Figure 3-11 shows the relationship of mud weight, viscosity, and screen mesh on shaker capacity.
SCREEN CAPACITY Screen Capacity, or the volume of mud which will pass through a screen without flooding, varies widely depending on shaker model and drilling conditions. Drilling rate, mud type, weight and viscosity, bit type, formation type, screen mesh — all affect throughput to some degree. 3.12
Figure 3-11 Shaker Capacity v. Mud Weight, Viscosity, and Screen Mesh
Mud type also has an effect on screen capacity. Higher viscosities generally associated with oil-base and invert emulsion mud usually result in lower screen throughput
than would be possible with a waterbase mud of the same mud weight. Some mud components such as synthetic polymers also have an adverse effect on screen capacity. As a result, no fine mesh screen can offer a standard throughput for all operating conditions. Due to the many factors involved in drilling conditions, mud characteristics and features of certain models, capacities on fine screen shakers can range from 50 to 800 GPM. Multiple units, most commonly dual or triple units, can be used for higher throughput requirements. Cascade shaker arrangements, with scalping shakers installed upstream from the fine screen shakers, can also increase throughput.
THREE-DIMENSIONAL SCREEN PANELS To increase screen capacity without increasing the size or number of shale shakers, three-dimensional screen panels are available. The design of these 3-D, Pinnacle™ shaker screens: • Provides even distribution of fluid across the screen surface • Eliminates unwanted fluid loss near the screen edges • Improves dryness of solids discharge • Allows the use of finer screens 3-D screen panels increase the
usable screen area of a screen panel by corrugating the screen surface, similar to the surface of a pleated air filter or oil filter. 3-D screen panels are most effective when installed as the submerged, feed-end screen on linear-motion shakers to take full advantage of the additional screen area. Past the fluid end point, a three-dimensional screen tends to “channel” the drilled solids and increases solids bed depth and the amount of liquid carried off the screen surface. Using a flat screen at the discharge end of the shaker eliminates channeling, increases cuttings dryness, and decreases fluid loss.
STANDARDIZATION Standardization of screen cloth designations has been recommended by the API committee on Standardization of Drilling Fluid Materials, in API RECOMMENDED PRACTICE 13E (RP13E), THIRD EDITION, MAY 1, 1993. The purpose for this practice is to provide standards for screen labeling of shale shaker screen cloths. The procedures recommended for labeling allow a direct comparison of separation potential, the ability to pass fluid through a screen, and the amount area available for screening. The API screen labeling includes of the following: 3.13
1. 2. 3.
Manufacturer’s designation; Separation Potential and Flow Capacity.
The Manufacturer’s designation contains the individual company’s procedures for naming their screens. It may include the type of screen panel, composition and other data required by the manufacturer. The API separation potential is reported in the terms of three “Cut” points. The term “Cut” point is not the same as the traditional cut point. The “Cut” point allows a ranking of a screen’s separation potential that can be used to compare screen performance. Three values (D50, D16, and D84) imply the opening sizes and variation in opening size of the screen. Flow capacity is the rate at which a shaker can process mud and solids. Under constant conditions, a shale shaker has a flow capacity that depends upon screen conductance and area. The area available for screening is the net unblocked area, in square feet, available for fluid passage through the screen panel. Conductance defines the ease of passage of a fluid through a piece of wire cloth. Conductance is calculated from the mesh count and wire diameters of the screen. Transmittance is the product of conductance times panels area. 3.14
These designations give the end user a more accurate assessment of solids removal capability and liquid throughput capacities of competitive screens.
3.3 SHALE SHAKERS The first line of defense for a properly maintained drilling fluid has been, and will continue to be, the shale shaker. Without proper screening of the drilling fluid during this initial removal step, reduced efficiency and effectiveness of all downstream solids control equipment on the rig is virtually assured. The shale shaker, in various forms, has played a prominent role in oilfield solids control schemes for several decades. Shakers have evolved from small, relatively simple devices capable of running only the coarsest screens to the models of today. Modern, high-performance shakers of today are able to use 100 mesh and finer screens at the flowline in most applications. This evolutionary process has taken us through three distinct eras of shale shaker technology and performance as shown in Figure 3-12. These eras of oilfield screening development may be defined by the types of motion produced by the machines: • Elliptical, “unbalanced” design • Circular, “balanced” design. • Linear, “straight-line” design
Figure 3-12 Shale Shakers
The unbalanced, elliptical motion machines have a downward slope as shown in Figure 3-12, A. This slope is required to properly transport cuttings across the screen and off the discharge end. However, the downward slope reduces fluid retention time and limits the capacity of this design. Optimum screening with these types of shakers is usually in the 30–40 mesh (400–600 micron) range. The next generation of machine, introduced into the oilfield in the late 1960s and early 1970s, produces a balanced, or circular, motion. The consistent, circular vibration allows adequate solids
transport with the basket in a flat, horizontal orientation, as shown in Figure 3-12, B. This design often incorporates multiple decks to split the solids load and to allow finer mesh screens, such as 80–100 square mesh (150–180 micron) screens. The newest technology produces linear, or straight-line, motion, Figure 3-12, C. This motion is developed by a pair of eccentric shafts rotating in opposite directions. Linear motion provides superior cuttings conveyance and is able to operate at an uphill slope to provide improved liquid retention. Better conveyance and longer fluid retention allow the use of 200 square mesh (74 micron) screens. Today, shale shakers are typically separated into two categories: Rig Shakers and Fine Screen Shakers.
RIG SHAKERS The rig shaker is the simpler of two types of shale shakers. A rig shaker (also called “Primary Shale Shaker” or “Coarse Screen Shaker”) is the most common type of solids control equipment found on drilling rigs. Unless it is replaced by a fine screen shaker, the rig shaker should be the first piece of solids control equipment that the mud flows through after coming out of the hole. It is usually inexpensive to operate and simple to maintain. 3.15
MUD TANK (POSSUM BELLY) MOTOR VIBRATOR ASSEMBLY BELT GUARD SCREEN BASKET ASSEMBLY LIQUID and FINE SOLIDS DISCHARGE CHUTE COARSE SOLIDS DISCHARGE Figure 3-13 Rig Shaker components
Standard rig shakers generally have certain characteristics in common (see Figure 3-13): • Single rectangular screening surface — usually about 4’ x 5’ in size. Some designs have utilized dual screens, dual decks and dual units in parallel to provide more efficient solids separation and greater throughput. Depending on the particular unit and screen mesh used, capacity of rig shakers can vary from 100–1600 GPM or more. • A low-thrust horizontal vibrator mechanism, using eccentric weights mounted above, or central to, the screen basket. • Vibration supports to isolate the screen basket from its skid. 3.16
Skid with built-in mud box (sometimes called a “possum belly”) and a bypass mechanism. Method of tensioning screen sections.
Screen sizes commonly used with rig shakers range from 10 to 40 mesh. Figure 3-14 shows the particle sizes separated by these mesh screens. In this graph the area to the left of each line represents solids which are smaller than that mesh size. These would pass through the screen and would not be removed. The area to the right of each line represents solids that are larger than the mesh size and would be removed from the mud. In Figure 3-14, the area to the
Figure 3-14 Particle Removal by Rig Shaker Screens
right of the 10 mesh line is confined, because it is limited by the size of the page. In actual usage, this area is unlimited. This means that a 10 mesh screen will remove all particles larger than 1910 microns — it doesn’t matter if they are the size of BBs, marbles or baseballs — they will be removed and discarded by a 10 mesh screen. Rig shakers are generally adequate for top hole drilling and for shallow and intermediate depth holes when backed up by other solids control equipment. For deeper holes and when using expensive mud systems, fine screen shakers are preferred.
FINE SCREEN SHAKERS The fine screen shaker is the more complex and versatile of the two types of shale shakers. Fine
screen shakers remove cuttings and other larger solids from drilling mud, but are designed for greatly improved vibratory efficiency over simple rig shakers. They are constructed to vibrate in such a way that they can use screens as fine as 150–200 mesh and still give reasonable screen life. They are versatile pieces of equipment and can operate on all types of mud. Figure 3-15 shows the range of particle sizes separated by the screens commonly used with fine screen shakers. A fine screen shaker can be installed on the rig in one of four ways: 1. Instead of the conventional rig shaker for use from top hole to total depth, if it is of a design capable of using coarse screens as well as fine screens. 3.17
Figure 3-15 Fine Screen Shaker Particle Separation
Placed in series with the rig shaker by tapping into the flow line with a “Y”, thus keeping the rig shaker available as a “scalping shaker”. Replacing the rig shaker after top hole is completed. Downstream from the rig shaker to accept fluid after it passes through the coarse screen shaker (requires secondary pump).
Because fine screen shakers have a wide variety of designs, they have few characteristics in common. The various designs are differentiated by screen orientation and shape, screen tensioning mechanism, placement and type of vibrator and other special features. Screen Orientation and Shape refers to the arrangement of the 3.18
screen or screens in the unit. Screens are usually rectangular and may be single screens or multiple screens placed in series or in parallel, as shown in Figure 3-16. Single deck, single screens (Figure 3-16 A & B) are the simplest design, with all mud passing over one screen of uniform mesh. This type of shaker requires efficient vibrator mechanisms to function properly under all possible drilling conditions and requires high throughput (Conductance) per square foot of screen cloth. Units with screens placed in parallel (Figure 3-16 C, D & E) have two or more screen sections acting as one large screen so that no cuttings can fall between them. All screen sections should be the same mesh, since the coarsest mesh section determines the unit’s screening ability.
Shakers with screens stacked in series (Figure 3-16 F) have a coarse screen above a finer screen, with the finer screen being the controlling mesh size. The operating theory is that the top screen will remove some of the cuttings from the mud to take part of the load off the bottom screen and thereby increase overall screening efficiency.
SCREEN TENSIONING MECHANISMS
Shakers are designed to use either a hookstrip or a rigid panel screen. Hook strip screens are made without a rigid frame and can prematurely fail if installed and allowed to operate with uneven tension. The shaker manufacturer’s instructions for screen installation should be followed, but the following steps may apply: • Inspect the supports and ten-
sion rails to be sure they are in good condition and clean Position the panel on the deck and inspect the screen to be sure it lays flat Install both rails loosely to the hookstrip Push one side of the screen against the positioning blocks, if present; and fully tighten the screen against these blocks Evenly tighten the tension bolts on the other side Torque to the manufacturer’s recommended setting
Rigid panel screen installation should proceed as per the manufacturer’s instructions. Panel screens can usually be installed or replaced much quicker than a hookstrip screen since the cloth is already pretensioned and the mechanical devices lock the panel with much less manual effort.
Figure 3-16 Shaker Screen Configurations
VIBRATOR MECHANISMS Vibrator Mechanisms vary widely in design and placement and greatly affect the throughput efficiency of fine screen shakers. Most modern shakers utilize linear motion vibration with the vibrator mechanism mounted above the screen bed. One important advantage of linear motion is positive conveyance of cuttings across the screen surface even when the surface is at a positive angle. This generally allows the use of an uphill sloped screen deck, greatly increasing throughput capacity and cuttings dryness. Most vibrators are electrically operated, although a few are hydraulically operated. In some units the vibration-inducing eccentric weights are separated from the drive motor, while in others the eccentric weights and motor form an integral assembly. In some units, the nature of the vibratory motions can be easily modified to take advantage of specific solids-conveying characteristics, but most units have a fixed vibratory motion.
MAINTENANCE Because of their greater complexity and use of finer mesh screens, fine screen shakers generally require more attention than rig shakers. Nonetheless, their more effective screening capabilities 3.20
more than justify the higher operating cost. This is especially true when expensive mud systems are used. Besides periodic lubrication, fine screen shakers require the same minimum maintenance as rig shakers while making a trip: • Wash down screens. • Check screen tension. • Shut down shaker when not drilling to extend screen life. • Dump and clean possum belly. In addition, frequent checks must be made for screen plugging and blinding, screen flooding and broken screens. All will occur more frequently on fine screen shakers than on coarse mesh rig shakers.
GENERAL GUIDELINES General rules in operating shale shakers — whether coarse screen rig shakers or fine screen shakers — which have not already been mentioned, include the following: • Use the finest mesh screen capable of handling the full volume from the flow line under the particular drilling conditions. This will reduce solids loading on downstream hydrocyclones and screens, improving their efficiency. Several screen changes, normally to progressively finer mesh screens over the course
of the hole, are quite common. Large cuttings which settle in the mud box (possum belly) of the shaker should never be dumped into the mud system. (Dump them into the sump or waste pit.) Except in extenuating circumstances (such as the presence of lost circulating material), all mud should be screened. This includes make-up mud hauled in from other locations. Unless water sprays are absolutely necessary to control screen blinding, water should not be used on the screen surface while drilling. Water sprays tend to wash smaller cuttings through the screen which would otherwise be removed by their clinging to larger particles (piggy-back effect).
For a more complete analysis of different types of screens and shakers, ask your local Brandt / EPI™ representative for copies of the latest Product Bulletins.
3.4 MUD CLEANERS AND MUD CONDITIONERS In many cases, combinations of vibratory screening and settling/ centrifugal force are used together to provide an effective separation. The most familiar combination sep-
arator is the Mud Cleaner or Mud Conditioner (Figure 3-17). Mud cleaners were developed in the early 1970s to remove fine drilled solids from weighted mud without excessive loss of barite and fluid. They have also proved valuable tools in closed systems and other “dry” location” applications. These devices use a combination of desilting hydrocyclones and very fine mesh vibrating screens (120–400 mesh) to remove fine drilled solids while returning valuable mud additives and liquids back to the active mud system. Traditional mud cleaners use multiple 4” or 5” cyclones, mounted over a vibrating screen, and are able to effectively process 400–600 GPM. The process capacity is limited by screen capacity and its ability to discard “dry” solids. With the introduction of linear motion vibrating screens, the capacity of the mud cleaner screen has been greatly increased. This, in turn, allows the use of additional hydrocyclones and higher, overall process capacities. The combination of hydrocyclones and linear-motion vibrating screens is called a Mud Conditioner to differentiate these machines from earlier mud cleaners. Mud conditioners often combine both desander and desilter cones mounted above the screen deck to take 3.21
full advantage of the higher process capacity, usually 1000–1500 GPM, and reduce the overall size and weight of the unit, when compared to mud cleaners. After removal of large cuttings with a shaker, feed mud is pumped into the mud cleaner/conditioner’s hydrocyclones with a centrifugal pump. The overflow from the cyclones is returned to the mud system. Instead of simply discarding the underflow, the solids and liquid exiting the bottom of the cyclones are directed onto a fine screen. Drilled solids larger than the screen openings are discarded; the remaining solids, including most barite in a weighted system, pass through the screen and are returned to the mud system. The cut point and amount of mass solids removed by a mud cleaner/ conditioner depends primarily on the mesh of the fine screen used, Figure 3-18. Since there are many designs of mud cleaners/conditioners available, performance and economics will vary with machine and drilling variables.
Figure 3-17 Mud Cleaners and Mud Conditioners
Mud cleaners/conditioners should be considered in these applications: 1. Whenever the application requires finer screens than the existing shaker can handle 2. Unweighted OBM
Figure 3-18 Particle Removal by Mud Cleaner Screens
3. 4. 5.
Expensive polymer systems When the cost of water is high Unweighted WBM with high disposal costs and/or environmental restrictions When use of lost circulation material requires bypassing the shaker Workover and completion fluid
Mud cleaners/conditioners are simply a bank of hydrocyclones mounted over a fine-mesh screen. In many instances (even with modern fine screen shakers), a finer separation is required than can be provided with existing shakers. The
question to answer becomes how to achieve the necessary level of screening at the lowest cost. The alternatives are: 1) Add additional similar shakers to handle the flow rate, 2) Replace the existing shakers with more efficient units or 3) Add a mud cleaner/conditioner downstream from the existing shakers. Any of these may be correct, but a thorough study of the capital cost (the actual cost of new equipment, plus transportation, rig modifications, and installation) and the operating cost (screens and other expendables, plus fuel) is necessary 3.23
to make the proper choice. Also, because of the cut points produced by some “modern” layered screens, the use of mud cleaner/conditioners may be indicated downstream of linear motion shakers. Salvage of the liquid phase of an unweighted drilling mud often costjustifies use of a mud cleaner/ conditioner when the fluid phase of the mud or disposal is expensive. Compared to desanders and desilters, whose cyclone underflow may be as much as 15 bbl/hr or more, mud cleaners/conditioners can achieve efficient solids removal while returning most liquid back to the active mud system. Use of ultrafine screens (200 to 325 mesh) significantly improves solids control in any high-value fluid system. An increasingly important application of mud cleaners/conditioners is the removal of drilled solids from unweighted water-base mud in semi-dry form. This system is commonly used in areas where environmental restrictions prohibit the use of earthen reserve pits, and expensive vacuum truck waste disposal from steel pits is the alternative. The mud cleaner/conditioner is used to discard drilled solids in semi-dry form which is classified as legal landfill in most areas and is subject to economical dry-haul disposal techniques (dump truck or portable waste containers). 3.24
When used for this purpose, the screen underflow from the mud cleaner/conditioner is often diverted to a separate steel waste pit for vacuum truck disposal. This may seem counterproductive, but since a vacuum truck can only carry a limited amount of sand because of the over-the-road weight restrictions, whenever a vacuum truck must haul normal full-flow desilter waste, the waste must be diluted with rig water to reduce density. The operator is then billed for the haulage of a vacuum truck load comprised largely of rig water. On the other hand, since most of the solids are removed in semi-dry form by the mud cleaner/conditioner screen, the remaining solids in the screen underflow are dilute enough to be hauled away without watering them back. Vacuum truck loads often can be reduced to a small fraction of those required with full-flow desilting. This approach to dry-solids disposal can be carried further by using a centrifuge with a mud cleaner/conditioner to form a “closed” system which eliminates discarding of any fluid. These systems are being used increasingly in areas where liquid mud waste must be hauled a significant distance and is subject to a high disposal fee. In a closed system, underflow from the mud cleaner/conditioner
screen is diverted to a holding tank and then centrifuged, which results in disposal of very fine, semi-dry solids and return of liquid to the active system. Such a system virtually eliminates the need for reserve pits, minimizes dilution, eliminates vacuum truck services for disposal of liquid mud, and meets environmental constraints when drilling within ecologically sensitive areas. One special mud cleaner/conditioner application is the use of a double-deck unit for salvage of coarse lost circulation material (LCM). Usually when running LCM, the shale shaker is bypassed and drilled solids build up rapidly in the mud, necessitating a high level of dilution and new mud. Use of a two-deck mud cleaner/conditioner allows salvage of the LCM while minimizing the increase in solids content. Within the mud cleaner/conditioner, a coarse top screen is used to pre-screen the mud and remove the lost circulation material. This material is discharged back into the active system for recirculation downhole. The drilled solids, mud additives and liquid phase pass through the top screen onto the lower, finer mesh screen, where the drilled solids are separated out and discarded. The cleaned mud then flows back into the mud system and is re-blended with the salvaged
lost circulation materials. Another mud cleaner/conditioner application is the clean up of workover and completion fluids. In order to reduce costs associated with this expensive task, a mud cleaner running one or two ultrafine screens (200 over 325 mesh) can be used to remove most of the solids before they reach cartridge type filters. This application can significantly reduce filter replacement costs, reduce downtime in changing filters, and allow larger volumes of fluid to be cleaned at a faster rate.
INSTALLATION Installation of the mud cleaner/conditioner is made downstream of the shale shaker and the degasser. The same pump used to feed the rig’s desander or desilter is often reconnected to feed the mud cleaner/conditioner when weight material is added. (Most mud cleaner/conditioners are designed to also function as desilter on unweighted mud by rerouting the cone underflow or by removing or blanking off the screen portion of the unit. The mud cleaner/conditioner may then be used to replace or augment the rig’s desilter during top hole drilling.) Follow these guidelines when installing mud cleaner/conditioners to allow peak efficiency: 3.25
Size the mud cleaner/conditioner cyclones to process 110–125% of the full circulating flow rate. Take the mud cleaner/conditioner suction from the compartment receiving fluid processed by the degasser (Weighted Muds). When using mud conditioners that have both desander and desilter cones, use a separate feed pump for the desander cones and another feed pump for the desilter cones. The desander cone suction should be from the degasser discharge compartment. The desilter cone suction should be from the desander discharge compartment. Keep all lines as short and straight as possible. Install a guard screen with approximately 1/2” openings at the suction to prevent large trash from entering the unit and plugging the cones. Position the mud cleaner/conditioner on the pit high enough so the overflow manifold will gravity-feed fluid into the next downstream compartment at an angle of approximately 45°. Avoid vertical overflow discharge lines from hydrocyclones.
GENERAL GUIDELINES To operate mud cleaner/conditioners at maximum efficiency, remember these fundamentals: • Operate mud cleaners/conditioners continuously on the full circulating volume to achieve maximum drilled solids removal. • Operate mud cleaners/conditioners within the limits of the screen capacity. A mud cleaner/conditioner with a cyclone throughput of 800 GPM is of little value if the cone underflow exceeds the screen capacity, resulting in flooding and high mud additive losses. • Feed the cone underflow to the screen at a single point. Multiple feed points on the screening surface minimize use of the available screen area and reduce overall capacity and efficiency. • Screen throughput is reduced by increased solids content and viscosity. The cyclone underflow plays a critical role in overall mud cleaner/conditioner efficiency. It is often desirable to modify the performance characteristics of the cones to decrease the amount of ultra fines in the cone underflow. This minimizes near-size screen plugging and barite loss due to “piggy-backing”.
Do NOT judge screen efficiency simply on the basis of cuttings dryness or color. The total amount of drilled solids in the discarded material, along with the ratio of barite to drilled solids, must be determined to correctly evaluate economic performance. A technique for measuring and calculating these values is given in Appendix B of this handbook. (Note: This technique is also important when using 100–mesh, or finer, screens on shakers since these screens can also remove appreciable amounts.) Select the number of cones to be operated and the particular mesh screen to be used according to drilling conditions. As a general rule, use the finest mesh screen possible (to process the full circulating rate) and size the number of cones accordingly.
In some instances, a number of cones will have to be blanked off in order for the desired screen mesh to be used. This may involve an experimental determination of the number of cones and screen mesh to optimize performance. In some cases, more than one mud cleaner/conditioner will be needed. The following example illustrates the point:
Earlier mud cleaner designs with 12–16 cones over a single screen bed have not proven to be practical: the ultra-fine mesh screens simply cannot handle the underflow volume from the cones. One exception to this is the mud conditioner; a linear-motion shaker coupled with a manifold of properly designed hydrocyclones yields a high-performance Mud Cleaner/ Conditioner with sufficient capacity for even the largest drilling rigs. Follow these general guidelines for correct mud cleaner/conditioner operation: • Run the mud cleaner/conditioner continuously while drilling and for a short period of time while making a trip for “catch-up” cleaning. • Start up the shaker portion of the mud cleaner/conditioner before engaging the feed pump(s). • Shut down the feed pump(s) before turning off the vibrating screen portion of the mud cleaner/conditioner. Permit the screen to clear itself, then rinse the screen with water or oil sprays before shutting down the screen portion of the unit. • For peak efficiency, operate the cones with a spray rather than a rope discharge. This is just as important with a mud cleaner/conditioner as with desilters and desanders. 3.27
Check cones regularly for bottom plugging or flooding, since a plugged cone allows solids to return to the mud system. If a cone bottom is plugged, unplug it with a welding rod or similar tool. If a cone is flooding, the feed is partially plugged or the bottom of the cone may be worn out. When a significant amount of barite is added to increase mud weight, shut down the mud cleaner/conditioner for one or two full circulations. This permits the fresh barite to thoroughly mix with the system and reduce losses over the screen. Use low-volume sprays on the screen surface to reduce “piggy-backing” only if 1) this liquid addition to the mud is permissible, and 2) the resultant reduction in barite discard outweighs the resultant reduction in drilled solids discard. This must be determined experimentally on a case-bycase basis.
In some cases, adding a small stream of cleaned mud from the hydrocyclone overflow (reflux) provides the same reduction in “piggy-backing” without reducing the overall efficiency of the unit. 3.28
MAINTENANCE Maintenance of mud cleaners/ conditioners generally combines the requirements of desilters and fine screen shakers: • Periodic lubrication • Check screen tension • Inspect the screen to ensure it is free of tears, holes, and dried mud before start up • Shut down unit when not circulating to extend screen life • Check feed manifold for plugging of cyclone feed inlets • Check cyclones for excessive wear and replace parts as necessary
3.5 SEPARATION BY SETTLING AND CENTRIFUGAL FORCE Using vibrating screens to remove drilled solids from mud uses only one characteristic of solids particles — their size. Another factor which affects separation is particle density. Solids control devices which take advantage of both particle size and particle density speed up the settling process by application of centrifugal force. These devices utilize Stoke’s Law as the basis for their operation. Stoke’s Law defines the relationship of factors governing the settling velocity of particles in a liquid. This relationship may be stated in its simplest form as:
Larger particles (of the same density) settle more rapidly than smaller ones. High density solids settle more quickly than low density ones. High acceleration and low viscosity speed up the settling rate.
Settling pits, hydrocyclones, and centrifuges all utilize this principle in their operation. Settling pits simply use the force of gravity to separate solids. The larger and/or heavier a solid is, the faster it will settle through fluid in a settling pit. There is no way to speed up this natural settling process other than reducing the viscosity of the fluid, or flocculating the solid particles with the addition of chemicals. Settling pits are often large and require closure or remediation. The reduction in waste mud achieved through efficient solids control
greatly reduces the waste water remediation treatment costs.
3.6 SAND TRAPS A sand trap (Figure 3-19) is a settling tank, usually the first compartment of the first pit in the mud system. A shale shaker would normally sit on top of the sand trap and discharge into it. Sand traps can serve an important role in solids control by protecting downstream equipment against the results of torn shale shaker screens or by-passed shakers by removing large particles which could plug cyclones or other equipment downstream. In normal operation they also play a minor solids removal role by settling out a portion of the coarse drilled solids which pass through the shaker screen. Normally, sand traps should have a top weir over which mud can flow into the next compartment, a
Figure 3-19 Cutaway View of Sand Trap
slanted bottom, and a quick-opening, quick-closing dump valve or gate so that settled solids can be discharged with minimum fluid loss. In some highly sensitive environments, the extra liquids lost from dumping the sand trap cannot be allowed and the desander suction is arranged to allow processing of the sand without creating a lot of liquid waste.
3.7 HYDROCYCLONES Hydrocyclones (also referred to as cyclones or cones) are simple mechanical devices, without moving parts, designed to speed up the
settling process. Feed energy is transformed into centrifugal force inside the cyclone to accelerate particle settling in accordance with Stoke’s Law. In essence, a cyclone is a miniature settling pit which allows very rapid settling of solids under controlled conditions. Hydrocyclones are important in solids control systems because of their ability to efficiently remove particles smaller than the finest mesh screens. They are also uncomplicated devices, which make them easy to use and maintain. A hydrocyclone (see Figure 3-20)
CLEANED DRILLING MUD (OVERFLOW)
SAND AND SILT, DRIVEN TOWARD WALL AND DOWNWARD IN ACCELERATING SPIRAL
DRILLING MUD MOVES INWARD AND UPWARD AS SPIRALLING VORTEX
SAND AND SILT (UNDERFLOW)
Figure 3-20 Hydrocyclone
consists of a cylindrical/conical shell with a small opening at the bottom for underflow discharge, a larger opening at the top for liquid discharge through an internal “vortex finder”, and a feed nozzle on the side of the body near the cylindrical (top) end of the cone. Drilling mud enters the cyclone using energy created by a centrifugal feed pump. The velocity of the mud causes the particles to rotate rapidly within the main chamber of the cyclone. Heavy, coarse solids and the liquid film around them tend to spiral outward and downward for discharge through the solids outlet. Light, fine solids and the liquid phase of the mud tend to spiral inward and upward for discharge through the liquid outlet. Design features of cyclone units vary widely from supplier to supplier, and no two manufacturers’ cyclones have identical operating efficiency, capacity or maintenance characteristics. In the past, cyclones were commonly made of cast iron with replaceable liners and other wear parts made of rubber or polyurethane to resist abrasion. Newer designs are made entirely of polyurethane, and are less expensive, last longer, and weigh less. Most well designed oilfield cyclones operate most efficiently when 75 feet of inlet head (±5 ft) is
applied to the cone inlet. Centrifugal pumps must be properly sized for cones to operate efficiently. Centrifugal pumps are constant energy (head) devices and not constant pressure devices. Feed head is constant regardless of mud weight; pressure varies with mud weight. Although centrifugal pump theory and sizing exercises are beyond the scope of this text, if you are not able to properly size your centrifugal pump to create 75 feet of inlet head to your set of cyclones, it is highly recommended that you contact the Technical Services Staff at Brandt / EPI™ for assistance. Remember, more errors in hydrocyclone applications are made with centrifugal pumps, rather than with the cyclones themselves. The size of oilfield cyclones commonly varies from 4” to 12”. This measurement refers to the inside diameter of the largest, cylindrical section of the cyclone. In general — but not always — the larger the cone, the coarser its cut point and the greater its throughput. Typical cyclone throughput capacities are listed in Figure 3-21. Manifolding multiple cyclones in parallel can provide sufficient capacity to handle the required circulating volume plus some reserve as necessary. Manifolding may orient the cyclones in a vertical 3.31
CONE SIZE (I.D.)
FEED PRESSURE (PSI)
Figure 3-21 Hydrocyclone Capacities
position or nearly horizontal — the choice is one of convenience, as it does not affect cyclone performance. The internal geometry of a cyclone also has a great deal to do with its operating efficiency. The length and angle of the conical section (and the ratio of cone diameter to cone length), the size and shape of the feed inlet, the size of the vortex finder, and the size and adjustment means of the underflow opening all play important roles in a cyclone’s effective separation of solids particles. Operating efficiencies of cyclones may be measured in several different ways, but since the purpose of CONE SIZE (I.D.) CUT POINT (MICRONS)
a cyclone is to discard maximum abrasive solids with minimum fluid loss, both solids and liquid aspects of removal must be considered. (A simple technique for comparing the efficiencies of two cyclones is given in Appendix B of this handbook.) In a cyclone, larger particles have a higher probability of reporting to the bottom underflow (apex) opening, while smaller particles are more likely to report to the top (overflow) opening. The most common method of illustrating particle separation in cyclones is through a cut point curve. Figure 3-22 shows the approximate cut point ranges for cyclones used with unweighted water-base
Figure 3-22 Hydrocyclone Capacities
mud and operated at 75 feet ±5 feet of inlet head.
HYDROCYCLONE CUT POINT Particle separation in cyclones can vary considerably depending on such factors as feed head, mud weight, percent solids, and properties of the liquid phase of the mud. Generally speaking, increasing any of these factors will shift the cut point curve to the right, increasing the size of solids actually separated by the cyclone. By itself, the cut point does not determine a cyclone’s overall efficiency because it ignores the liquid loss rate. The amount of fluid in the cone underflow is important; if the solids are too dry, they can cause “roping” or “dry-plugging” of the underflow. In contrast, a cyclone operating with a spray discharge (see Figure 3-23) gives solids a free path to exit. A cone operating in spray discharge will remove a significantly greater amount of solids than a cone in “rope” discharge.
ROPE DISCHARGE Hydrocyclones should not be operated in rope discharge because it will drastically reduce the cone separating efficiency. In a rope discharge, the solids become crowded at the apex, cannot exit freely from the underflow, and become caught
NO CROWDING AT THE APEX
CROWDING AT THE APEX
Figure 3-23 Spray v. Rope Discharge
by the inner spiral reporting to the overflow. Solids which otherwise would be separated are forced into the overflow stream and returned to the mud system. This type of discharge can also lead to plugged cones and much higher cyclone wear. While a spraying cyclone appears to discharge more fluid, the benefits of more efficient solids removal and less cone wear outweigh the additional fluid loss. In cases where a dry discharge is required, the underflow from hydrocyclones can be screened or centrifuged to recover the free liquid.
3.8 DESANDERS Desanders are hydrocyclones larger than 5” in diameter (6”, 8”, 10” or 12” ID). Generally, the smaller the cone, the smaller size particles the cone will separate (see Figure 3-24). Desanders are primarily used to
Figure 3-24 Particle Removal by Desander Cyclones (200 Mesh Screen Included for Comparison)
remove the high volumes of solids associated with extremely fast drilling of a large diameter hole. Desanders are installed downstream from the shale shaker and degasser. The desander removes sand sized particles and larger drilled solids which have passed through the shaker screen and discards them along with some liquid into a waste pit. The partially clean mud is discharged into the next pit downstream.
INSTALLATION When installing a desander, follow these general recommendations: • Size the desander to process 110–125% of the total mud circulation rate. 3.34
Keep all lines as short and straight as possible with a minimum of pipe fittings. This will reduce loss of head on the feed line and minimize backpressure on the overflow discharge line. Do not reduce the diameter of the overflow line from that of the overflow discharge manifold. Direct the overflow line downward into the next downstream compartment at an angle of approximately 45°. The overflow discharge line should not be installed in a vertical position — doing so may cause excessive vacuum on the discharge header and pull solids
through the cyclone overflow, reducing the cyclone’s efficiency. Keep the end of the discharge line above the surface of the mud to avoid creating a vacuum in the line. Position the underflow trough to easily direct solids to the waste pit. Install a low equalizer line to permit backflow into the desander suction. Operating desanders at peak efficiency is a simple matter, since most desanders are relatively uncomplicated devices.
Here are a few fundamental principles to keep in mind: • Operate the desander unit at the supplier’s recommended feed head (usually around 75 feet). Too low a feed head decreases efficiency, while excessive feed head shortens the life of cyclone wear parts. • Check cones regularly to ensure the discharge orifice is not plugged. • Run the desander continuously while drilling and shortly after beginning a trip for “catch-up” cleaning. • Operate the desander with a spray rather than a rope discharge to maintain peak efficiency.
MAINTENANCE Maintenance of desanders normally entails no more than checking all cone parts for excessive wear and flushing out the feed manifold between wells. Large trash may collect in feed manifolds which could cause cone plugging during operation. Preventive maintenance minimizes downtime, and repairs are simpler between wells than during drilling. Use of desanders is normally discontinued when expensive materials such as barite and polymers are added to a drilling mud, because a desander will discard a high proportion of these materials along with the drilled solids. Similarly, desanders are not generally cost effective when an oil-base mud is in use, because the cones also discard a significant amount of the liquid phase.
3.9 DESILTERS A desilter uses smaller hydrocyclones (usually 4” or 5” ID) than a desander and therefore generally removes smaller particles. The smaller cones enable a desilter to make the finest particle size separation of any full flow solids control equipment — removing solids in the range of 15 microns and larger (Figure 3-25). This makes it an important device for reducing average particle size and removing 3.35
Figure 3-25 Particle Removal by Desilter Cyclones (200 Mesh Screen Included for Comparison)
abrasive grit from unweighted mud. The cyclones in desilter units operate on the same principle as the cyclones used on desanders. They simply make a finer cut, and the individual cone throughput capacities are less than desander cones. Multiple cones are usually manifolded in a single desilter unit to meet throughput requirements. Desilters should be sized to process 110–125% of the full rig flow rate.
INSTALLATION Installation of desilters is normally downstream from the shale shaker, sand trap, degasser and desander, and should allow ample space for maintenance. Here are some fundamentals for installing desilters: 3.36
Take the desilter suction from the compartment receiving fluid processed by the desander. Do NOT use the same pump to feed both the desander and desilter. If both pieces of equipment are to be operated at the same time, they should be installed in series and each should have its own centrifugal pump. Keep all lines as short and straight as possible. Install a guard screen with approximately 1/2” openings at the suction to the desilter to prevent large trash from entering the unit and plugging the cones.
Position the desilter on the pit high enough so the overflow manifold will gravity-feed fluid into the next downstream compartment at an angle of approximately 45°. Remember — no vertical overflow discharge lines. Keep the end of the discharge line above the surface of the mud to avoid creating a vacuum in the line. Install a low equalizer line for backflow to the desilter’s suction compartment. Position the underflow trough to easily direct solids to the waste pit.
Running a desander ahead of a desilter takes a big load off the desilter and improves its efficiency. If the drilling rate is slow and the amount of solids being drilled is only a few hundred pounds per hour, then the desander may be turned off (to save fuel and maintenance costs) and the desilter may be used to carry the total desanding/desilting load. Appendix C includes a chart to calculate the pounds per hour of solids generated for a range of hole size and rate of penetration. Operating efficiencies of competitive desilters vary widely according to differences in design features. The same technique described in
Appendix B for comparing two desanders will work to compare the efficiencies of competing desilters operating on the same rig.
GUIDELINES To operate desilters at maximum efficiency, follow these basic guidelines: • Operate the cones with a spray discharge. Never operate the desilter cones with a rope discharge since a rope underflow cuts cone efficiency in half or worse, causes cone plugging, and increases wear on cones. Use enough cones and adjust the cone underflow openings to maintain a spray pattern. • Operate the desilter unit at the supplier’s recommended feed head. This is generally between 70–80 feet of head. Too much energy will result in excessive cone wear. • Check cones regularly for bottom plugging or flooding, since a plugged cone allows solids to return to the mud system. If a cone bottom is plugged, unplug it with a welding rod or similar tool. If a cone is flooding, the feed is partially plugged or the bottom of the cone may be worn out. • Run the desilter continuously while drilling and also for a short while during a trip. The 3.37
extra cleaning during the trip can reduce overload conditions during the period of high solids loading immediately after a trip.
MAINTENANCE A desilter’s smaller cyclones are more likely than desander cones to become plugged with oversized solids, so it is important to inspect them often for wear and plugging. This may generally be done between wells unless a malfunction occurs while drilling. The feed manifold should be flushed between wells to remove trash. Keep the shale shaker well maintained — never bypass the shaker or allow large pieces of material to get into the active system. A desilter will discard an appreSCROLL
ciable amount of barite, because barite particles fall within the silt size range. Desilters are therefore not recommended for use with weighted mud. Similarly, since hydrocyclones discard some absorbed liquid along with the drilled solids, desilters are not normally used with oil-base mud, unless another device (centrifuge or mud cleaner/conditioner) is used to “deliquor” the cone underflow.
3.10 DECANTING CENTRIFUGE Centrifuges for oilfield applications were first introduced in the early 1950s. These early units were adapted from existing industrial decanting centrifuges. In the mid1960s, a perforated rotor type machine was developed which SCROLL FEED CHAMBER BOWL WEIRS FEED PIPE DRILLING MUD
Figure 3-26 Decanting Centrifuge
does not perform like a pure decanter. Commonly called “barite recovery” centrifuges, these early designs were limited in capacity and application. Today, the centrifuge is even more important part of solids control. In addition, the increased use of low-solids mud and environmental dewatering applications require higher process volumes, greater clarification and solids capacity, and additional fine solids removal. Equipment selection is decided by site specific requirements. Proper system selection is the first step to effective solids control.
SEPARATION PROCESS A Decanting Centrifuge is so named because it Decants, or removes, free liquid from separated solids. A decanting centrifuge consists of a conveyor screw inside a rotating bowl, see Figure 3-26. Decanting centrifuges operate on the principle of exposing the process fluid to increased “Gforces”, thus accelerating the settling rate of solids in the fluid. A rotating bowl creates high G-forces and forms a liquid pool inside the bowl. The free liquid and finer solids flow toward the larger end of the centrifuge and are removed through the effluent overflow weirs. The larger solids settle against the bowl
wall, forming a layer. These solids are pushed by a screw conveyor across a drainage deck, or beach. Dewatering actually takes place on the beach, with the decanted solids discharged through a series of underflow ports. A gear box changes the relative speed of the conveyor to the bowl, causing them to rotate at slightly different rates. This speed differential is required to convey and discharge solids. The bowl and conveyor are rotated at speeds between 1500 and 4000 rpm depending on bowl diameter. This rotation develops centrifugal force sufficient to settle solids along the inner surface of the bowl wall. A gearbox is used to rotate the conveyor and bowl at slightly different speeds (slower or faster). This speed differential conveys and discharges solids from the machine. Mud, (sometimes diluted with water), is pumped into the conveyor hub through the feed tube. As the conveyor rotates, centrifugal force pushes the feed mud out the feed ports into the bowl. The heavy, coarse particles in the mud are forced against the inner surface of the bowl, where the scraping motion of the conveyor blades moves them toward the solids discharge ports. A drainage deck, called the beach, is where dewatering of the solids actually takes 3.39
place. The deliquified solids are then discharged through a series of underflow ports. The light, fine solids tend to remain in suspension in the pools between the conveyor flights and are carried out the overflow ports along with the liquid phase of the mud. The operating principle is similar to that of the cyclone, but it is mechanical rotation rather than fluid head which induces the centrifugal force required to accelerate the particle settling rate. Residence time of fluid in the bowl and a more “gentle” separation environment differentiate separation in a centrifuge from that of a cyclone. Centrifuges make the finest cut of any separation device used on the rig, usually 2–5 microns. Bowl sizes in common oilfield applications include diameters of 14”, 15”, 18”, and 24”. Larger 24” diameter units generally have the highest liquid throughput and solids tonnage capacity. In unweighted mud applications, feed mud capacity can range from 25–250 gpm, depending on unit capability and fluid requirements. Solids tonnage rates range from 1.25 tons/hour to 8 tons/hour. In weighted mud applications, feed mud capacity rarely exceeds 25 GPM. Total liquid throughput may be as high as 40 GPM, including dilution liquid. Dilution liquid is 3.40
required to compensate for increasing viscosity, generally associated with increasing mud weight, in order to maintain satisfactory separation efficiency. The raw mud feed rate is substantially decreased as mud weight increases. In field operation, the decanting centrifuge is fitted with a housing over the bowl, liquid and solids collection hoppers, skid, feed slurry pump, raw mud and dilution liquid connections, power source, meters and controls.
WEIGHTED MUD APPLICATIONS The classic application of centrifuges while drilling takes advantage of their ability to make a very fine cut — on the order of 5–10 microns — when treating weighted water-base mud. In this application, centrifuges are used intermittently to process a small portion of the volume circulated from the well bore to reduce the amount of colloidal-sized and improve the flow properties of the mud. Viscosity can be effectively controlled by discarding a relatively small amount of colloidal size solids and replacing the discarded liquid with fresh make-up water. To remove these colloidal solids, the liquid fraction from the decanter (or the lighter slurry fraction from the perforated cylinder
centrifuge) is discarded. The sandsize and silt-size semi-dry solids fraction from the decanter (or the heavier slurry fraction from the perforated cylinder centrifuge) is returned to the active system. Installation of a centrifuge is usually downstream from all other solids control equipment. Ideally, suction for a centrifuge mud feed would be taken from the same pit or compartment which receives the discharge from a mud cleaner/conditioner. The centrifuge underflow (solids) should be discharged to a wellstirred spot in the pit for thorough mixing with whole mud before the solids have a chance to settle out in the bottom of the pit. This is especially important with a decanter, which discharges damp solids, and of lesser importance with a perforated cylinder centrifuge, which discharges a pumpable slurry. With either type of machine, the underflow discharge should not be too close to the rig pump suction. The overflow (liquid/colloidal solids) gravity-feed down a constantly sloping chute or pipe to waste. Sufficient working space should be provided for routine maintenance and operating adjustments to the centrifuge. Operation of centrifuges in this application is generally intermittent rather than continuous. This again relates to the standard purpose of
the centrifuge — to control viscosity by removal of colloidal size particles. Centrifuges should be run when viscosity reaches the operator-established maximum, and the machine’s operation should be stopped when viscosity reaches the established minimum. The maximum and minimum limits should be established as part of the overall mud program. Viscosity will normally creep up when centrifuges are shut down due to the size degradation of mud solids, hence the need for restarting the unit. Both over-centrifuging and under-centrifuging should be avoided, as the economics of operation are greatly reduced under these circumstances. When centrifuging a weighted mud, bentonite and chemicals must be added back to the mud system. The amount of replacement bentonite may be calculated exactly from mass balance equations, but a good rule of thumb is to add about one sack of bentonite per hour of centrifuge operation. “Under-centrifuging” simply will not achieve the desired reduction in viscosity. Other applications of decanting centrifuges have become more important in recent years because of the decanter’s ability to remove free liquid from the solids discharge. As part of a “closed loop”, the decanting centrifuge is used to dewater the 3.41
under-flow from hydrocyclones and remove ultra-fine particles from the active mud system. Multiple centrifuges are not uncommon, operated either in parallel or in series. Chemical enhancement (through the use of coagulants, flocculants, and other chemicals) is becoming more popular as an economical way to reduce dilution requirements and overall waste volume for haul-off and disposal. The main difference of centrifuge use in these applications versus their use for viscosity control in weighted mud is the continuous use of the centrifuge and the routing of the two discharge streams.
UNWEIGHTED MUD APPLICATIONS In the classic weighted mud application the solids discharge (containing the majority of the weighting material) is returned to the mud system. The liquid effluent (containing the majority of the colloidal size solids) is discarded. As part of a “closed loop”, larger high capacity (75–250 GPM) decanting centrifuges (and sometimes standard centrifuges) are used to maximize fine solids removal. The coarser solids fraction is discarded in dry form, while the liquid and colloidal solids fraction is returned to the mud system. Decanting centrifuges are becom3.42
ing more popular for processing unweighted oil mud, especially if 1) the mud has been brought in from another location and may contain a large amount of fine drilled solids, 2) slow, hard drilling with a gradual buildup of ultra-fine solids is anticipated or 3) the liquid mud phase is valuable.
WEIGHTED OIL-BASE MUD APPLICATIONS In weighted, oil-base mud applications, decanting centrifuges are operated in series. The first unit returns the coarse solids fraction (weight material ) to the active system, with the light, liquid fraction being routed to a holding tank (rather than being discarded as in a classic weighted mud application). A second unit, often a higher capacity machine, strips out the solids and discards them, returning the effluent to the active system. This process is not as effective as a single unit for viscosity control — a large portion of the colloidal size solids are returned to the active mud system in the effluent stream of the second unit — but the effluent stream from the first unit is too valuable to discard, especially with synthetic oil muds. Usually the coarse solids fraction is discarded and the base fluid is retained for reuse.
OPERATING PROCEDURES Operating procedures will vary from model to model, but a few universal principles apply to almost all centrifuges: • Before starting a centrifuge, rotate the bowl or cylinder by hand to be sure it turns freely. • Start up the centrifuge before starting the mud feed pump and dilution water feed. • Set the raw mud and dilution feed rates according to the manufacturer’s recommendations (usually variable with mud weight). • Remember to turn the feed and dilution water off before the machine is stopped. Centrifuges are relatively easy to operate, but they require special skills for repair and maintenance. Rig maintenance of centrifuges is limited to routine lubrication and speed adjustment of the unit.
3.11 AUXILIARY EQUIPMENT AGITATION/MIXING All compartments in an active mud system other than the sand trap must be agitated in order to suspend solids and maintain a consistent mixture throughout the surface system. Suspension of the solids prevents their settling and keeps them in the active mud system so that they can be separated
by mechanical solids control equipment.
MUD GUNS For many years Mud Guns (see Figure 3-27) were used as the sole means of agitation. These devices usually carry mud from a downstream compartment and spray it at high velocity into an upstream compartment to keep solids suspended. However, the true mixing effect of mud guns tends to be localized around the point where the nozzle spray discharges, leaving dead spots in other areas of the tank. Mud guns also increase the load on downstream solids Figure 3-27 Mud Gun control equipment, since each nozzle may add 100— 200 GPM of mud into the tank above and beyond the normal flow from the well.
MECHANICAL AGITATORS Mechanical Agitators (see Figure 3-28) provide more thorough mixing of pits without the problems associated with mud guns. Agitators use an electric motor to drive impeller blades which flow the mud in a pattern throughout the tank. 3.43
cy when pumping gas-cut mud, and the cones will not function properly if feed head fluctuates or if there is gas in the incoming mud. Also, recirculation of gas-cut mud is dangerous and could result in a blowout, since the density of gascut mud is lighter than the mud weight that should be maintained in the well bore. There are three basic methods of degassing which can be utilized separately or in combination. The three degassing techniques are: atmospheric, vacuum and cyclonic.
ATMOSPHERIC DEGASSERS Figure 3-28 Mechanical Agitator
Given proper tank design, agitator sizing, and impeller placement, this method of agitation prevents settling, enhances the efficiency of solids removal devices, and maintains a well blended mud system.
DEGASSERS After passing through a shale shaker and a sand trap, all drilling mud should be directed through a degasser, see Figure 3-29. Degassers are often essential to the solids removal process to ensure the proper performance of hydrocyclones used in downstream solids control devices. The centrifugal pumps that feed the cyclones have difficulty maintaining their efficien-
Atmospheric Degassers sit in the mud tank and consist of an elevated spray chamber and a submerged centrifugal pump. The gas-cut mud is pumped to the spray chamber at high velocity through a disc valve. The mud strikes the inside wall of the spray chamber with enough force to drive most of the entrapped gas out of the mud. The removed gas is usually discharged to atmosphere at pit level and the degassed mud returned to the active system. These devices are simple to operate and maintain, but their effectiveness is often limited by the ability of the centrifugal pump to handle gas-cut mud. A second method of degassing is provided by the use of a vacuum.
Figure 3-29 Degassers
VACUUM-TYPE DEGASSERS Vacuum-type Degassers separate gas bubbles from drilling mud by spreading the gas-cut mud into thin layers and then drawing off the gases with a vacuum pump. The mud is usually thinned by flowing it over a series of baffles or plates. Vacuum degassers are normally skid-mounted and installed on top of the mud tanks. Some models incorporate more than one degassing technique within a single unit. For example, one
degasser spreads the mud into thin sheets through centrifugal force, sprays the mud onto an impact shield for residual gas separation, and draws off the gases with a vacuum pump.
INSTALLATION Actual placement of the degasser and related pump will vary with the design of the degasser, but these recommendations may be used as a general rule: • Install a screen in the inlet pipe to the degasser to keep large 3.45
objects from being drawn into the degassing chamber. Locate the screen about one foot above the pit bottom and in a well-agitated spot. There should be a high equalizer line between the suction and discharge compartment. The equalizer should be kept open to allow backflow of processed mud to the suction side of the degasser. Route the liquid discharge pipe to enter the next compartment or pit below mud level to prevent aeration. Install the gas discharge line to safely vent the separated gas to atmosphere or to a flare line.
Maintenance of degassers varies considerably depending on make and model. In general, the following guidelines apply: • Check to make sure the suction screen is not plugged. • Routinely lubricate any pumps and other moving parts and check for wear. • Keep all discharge lines open and free from restrictions, such as caused by solids buildup around valves. • If the degasser utilizes a vacuum, keep it at the proper operating level, according to the manufacturer’s recommended range for the mud weight and process rate. 3.46
Check all fittings for air leaks. If the unit uses a hydraulic system, check it for leaks, proper oil level, and absence of air in the system.
DRYING SHAKERS A drying shaker, or dryer, is a vibrating screen separator used to remove free liquid from cuttings prior to discharge and recover the liquid for re-use. Drying shakers are usually installed to process the cuttings discharged from primary scalping and/or fine screen shakers. A typical drying shaker is a linearmotion, multi-screen unit, with a feed hopper in place of the traditional back tank. Drying shakers are optimized to provide maximum retention time and cuttings dryness. Large hole sizes or high penetration rates may require more than one drying shaker to provide acceptable cuttings dryness and liquid recovery. Shale shakers are often the cause of excess mud loss during drilling operations, primarily due to screening too fine for drilling conditions and the design of some shakers. This mud loss can greatly increase mud costs and site clean-up costs, especially when oil-base muds, OBM, or synthetic-base muds, SBM, are used. One characteristic of SBM is the increased amount of liquid retained on the cuttings, compared to WBM or conventional OBM.
The drying shaker is designed to expose wet drilled cuttings to an additional vibrating screen surface and separate some of the bound liquid coating the surface of the solids. The liquid is then returned to the active system or transferred to a storage tank for future use.
DRYING SHAKER DESIGN The first drying shakers were “high-G” units, operating at 6.5 to 8 Gs. Prevalent thinking was that the additional impact force provided by the higher G-force would improve cuttings dryness. Recent field studies indicate this is not necessarily true. Oil content on cuttings is primarily a function of retention time on the screen surface and the exposure of the cutting to the vibrational force of the shaker. The G-force greatly affects the speed at which cuttings move from the feed end of the screen surface to the discharge end. At 4 Gs, the conveyance rate is close to 1 inch per second, while at 7 Gs the conveyance rate is about 5 inches per second. Given a screen length of 24 inches and operation at 4 Gs, a cutting will take approximately 24 seconds to travel from the feed end of the screen to the discharge end. Increasing the G-force to 7 G’s reduces the exposure time to 6 seconds and will actually increase the
amount of oil remaining on the cuttings! Since the amount of oil remaining on the cutting is a function of exposure time, screen deck length and deck angle will greatly influence cuttings dryness. Screen deck length determines the distance a cutting must travel prior to discharge and deck angle influences retention time — the longer the screen deck and the steeper the deck angle, the greater the retention time. However, longer screen decks may not fit the available space and too steep a deck angle will result in cuttings grinding and unacceptable build-up of fine solids. Field tests indicate the optimum dryer design provides about 4–5 Gs of force, with a deck design that is flat at the feed end to reduce cuttings grinding and maximize usable screen area. The discharge screens should be sloped uphill at 2.5° to 5° to increase retention time and maximize cuttings dryness.
Locate the drying shaker(s) at a lower level from the main linear shakers and other solids control equipment. Feed to the drying shaker should be through open hopper sized to eliminate solids build-up or plugging. Cuttings should be 3.47
evenly deposited as close to the feed end of the drying shaker as possible to maximize usable screen area and cuttings dryness. Provide slides or conveyors to direct “dry” cuttings to solids collection bins or discharge chutes Supply a flooded pump suction in the liquid collection tank for transfer by pump to the desired storage or processing tank. The mesh of the screens on the drying shaker should be close to, or finer than, the screens on the main shakers to prevent the re-introduction of separated solids to the active system. Use three-dimensional, Pinnacle™ screen panels at the feed end of the dryer to usable increase screen area. The middle screen panel may be either a 3-D or flat panel, depending on deck angle and desired fluid end point. The discharge end screen should be a flat screen panel to minimize cuttings bed depth and maximize liquid recovery. Adjust screen deck angle design to properly convey solids, reduce liquid loss, and prevent cuttings grinding. The liquid recovered from the drilled cuttings will contain base fluid, plus any solids finer
than the screen mesh of the drying shaker. The recovered liquid should be processed through a decanting centrifuge to remove ultra-fine solids before the mud is returned to the active system or storage tank. In some installations, the decanting centrifuge may be eliminated, but only after careful consideration of cuttings size and their effect on fluid properties.
3.12 UNITIZED SYSTEMS Since 1976, several solids control manufacturers have developed complete packages of skid-mounted solids control devices, including all supporting tanks, piping, pumps, motors and accessories. These “unitized” systems maximize solids control efficiency, ease transportation and installation, and often provide a very high efficiency system for ecologically sensitive drilling sites. Components of unitized systems can vary depending on manufacturer and the particular drilling application, but most include one or more of the basic separation devices installed in series: fine screen shaker, degasser, desander, desilter, mud cleaner/conditioner, and centrifuge. Desilting requirements are usually met by blanking off the screens on the mud clean-
Figure 3-30 Brandt/EPI™ ISCS unitized System
er/conditioners and operating them as desilters as appropriate. Sand traps and agitators are also standard equipment in most units (See Figure 3-30). In well-designed systems, all pieces of equipment, including pumps and motors, are properly sized to provide the greatest degree of efficiency in the smallest amount of space. Piping is engineered for optimum fluid handling with the shortest practical suction and discharge lines. Normally the only installation required for these units is to feed the flow line from the well into the shale shaker, connect a discharge line from the unitized system into the rig suction pit, and make the electrical and water connections. The suction pit remains a necessary part of the surface system in order to provide mud volume capacity and as a place for mixing-in mud additives.
3.13 RIG ENHANCED SYSTEMS Recent advances in shaker design, along with the custom requirements of operators and increasing emphasis on environmental impact, have created another type of system — the Rig-Enhanced System. Like the unitized systems, Rig-Enhanced Systems (RES) are designed so all pieces of equipment, including pumps and motors, are properly sized to provide the greatest degree of efficiency in the smallest amount of space. However, RESs utilize as much of the existing rig equipment and tanks as possible to simplify installation, reduce equipment cost, and allow further customization of a system for a specific application. Suppliers of both systems commonly provide 24 hour on-site service for all components in the system, which greatly improves overall efficiency and simplifies maintenance procedures from the driller’s standpoint. Considering the 3.49
importance of solids control in deep drilling and the growing concern over environmental impact of mud waste disposal, these systems will be used more often in the future.
3.14 HIGH EFFICIENCY SOLIDS REMOVAL SYSTEMS The goal of high efficiency solids removal systems, often called “closed loop” systems, is to limit waste discharge to disposable solids and clear water. These systems combine the equipment found in Section 3.12 with chemicallyenhanced solids removal and specialized solids handling techniques. The water is often recycled on location for building new mud, as rig wash water, or used for irrigation. A “closed loop” system often includes multiple shale shakers and centrifuges to achieve a high efficiency of performance in the large upper hole sections of the well where wastes and circulating volumes are the greatest. Enhanced solids removal is accomplished with chemical addition to “pre-treat” the fluid prior to screening or centrifugation. Pretreatment can include pH adjustment, flocculation/coagulation, or similar treatment. Solids handling techniques include washing cuttings to remove excess chlorides or residual oil, 3.50
solidification, or cuttings discharge into water tight containers for transport to approved waste facilities. In addition to their primary goal, “closed loop” systems minimize drilled solids remaining in the drilling fluid. This reduces dilution requirements, waste volume, and drilling problems. Therefore, “closed loop” systems have many applications other than environmental ones. The benefit of a “closed loop” system comes from increased solids removal efficiency with unweighted fluids, including clear brines, and reduced discharge volume with weighted fluids. This performance has proven extremely effective in environmentally sensitive areas or whenever cuttings and liquid mud must be hauled from the location prior to disposal. This system provides best results when combined with constant, on-pit attention and supervision. Solids Removal Efficiency of 75–95% is typical, with a 50–55% Solids Discharge Concentration. Proper installation and operation are equally important. Here are a few guidelines to keep in mind: • Fines stay with the liquid; that is, the smallest particles (colloidal sized) usually remain with the liquid phase of the mud, while the larger particles — sand, cuttings, etc. — are removed from the liquid.
Size each piece of full-flow solids control equipment, except the centrifuges, to handle 110–125% of circulating volume (in order to handle backflow within compartments, volume from mud guns, etc.). Always use the finest mesh screen possible that will meet throughput and screen life requirements. Often when a solids control device fails to perform, as it should, the cause is improper installation, not equipment malfunction. Install equipment in proper sequence: as the mud moves downstream, each device removes progressively smaller particles. Never try to make a single device remove all particle sizes — it is better to allow each device to remove its particular size range within an overall solids control system. Each piece of solids control equipment should discharge into the next compartment downstream from where its suction is taken. All compartments other than the sand trap should be agitated, preferably by mechanical agitators. Keep all piping as short and straight as possible. Never install a 90° elbow or
valve within 5 feet of suction of a centrifugal pump, as this will drastically reduce the life of the pump. For maximum efficiency, cyclones should emit a spray discharge rather than a rope discharge. Use only as many cones on a mud cleaner/conditioner as required to meet flow capacity, in order to extend screen life and to avoid flooding the screen. Remember size constraints and possible sloshing and spillage in rough seas when designing offshore systems. Special winterizing measures — a shed around the pits, drains in pumps, steam lines, etc. — may be required in areas of extreme cold in order to ensure proper functioning of the solids control equipment. Size it, install it, operate it RIGHT!
3.15 BASIC ARRANGEMENT RULES Mechanical solids control is the most cost-effective method to control drilled solids. The benefits of proper solids control are discussed in detail in Section 2. Proper solids control requires: • Proper planning before the well begins 3.51
Proper selection, installation, and operation of available equipment Routine monitoring of fluid properties to optimize performance Sequential Treatment – It follows from previous recommendations that the solids control equipment should be arranged so that each piece of equipment removes successively finer solids. Compartment Mixing – To provide a uniform solids load to the equipment each compartment, except the sand trap, should be well stirred. If mud guns are used they should be arranged so that no flow bypasses the solids control equipment. Agitators are preferable. Arrangement – Each piece of solids control equipment must be arranged so that the suction is taken from a compartment upstream of the discharge compartment, i.e., there must be a wall or division with an equalizer opening between the suction and discharge, even if it is boards placed in the tank temporarily.
Upstream Flow Through Equalizer – If the flow into the suction compartment is greater than the rate of flow processed by the equipment, then mud is flowing downstream through the equalizer. In other words, the flow through compartment equalizers should always be from the discharge to the suction. If it is not then mud is bypassing the equipment. Dedicated Feed Pumps – Manifolding pumps and equipment so that multiple configurations are available depending on valve positions is always a mistake. There should be only one button to push to begin the pump and the discharge valve opened slowly to begin operation of the solids control unit. Use a separate centrifugal pump for each hydrocyclone device (do not use the same pump for more than one piece of equipment).
Equipment selection is decided by site-specific requirements. Proper system selection is the first step to effective solids control.
Equipment and Services for Solids Control and Waste Management
COMPANY PROFILE 4.1 Scope of Services: Brandt/EPI™ specializes in the design, manufacture, and service of solid/liquid separation systems, related equipment, and site remediation services for exploration, production, and industrial applications. We have the technical expertise to provide engineering services, system design and operation, and proprietary technologies to our clients throughout the world. For over 20 years, Brandt/EPI personnel have been providing industry with solid solutions to separation and remediation problems. Our diversified experience and proven track record allow us to offer a wide range of project capabilities including: Equipment and Systems Vibrating Screen Separators Hydrocyclone Separators Centrifugal Separators Dewatering Units Filtration Units Integrated Systems Other Products Technical and Engineering Services Equipment Recommendations
On-site Technical Support Pilot Studies Project Proposals Process Recommendations Project Installation and Start-Up System and Equipment Design Site Remediation Services Bioremediation Dewatering Systems Landfarming Pond Closures Slurrification and Injection Sludge Fixation Soil/Sand washing Waste minimization Water Treatment
4.2 Business Relationships: We believe in long-term partnerships with clients and vendors, and place strict emphasis on providing cost-effective products and services to meet the needs of our clients, regulatory agencies, our employees, and the community. Emphasis on quality and innovative solutions has established Brandt/EPI as a performance-oriented company with strong bottom-line focus.
4.3 Certifications: Quality products and services are our priority. Through its parent 4.1
company, Brandt/EPI maintains several corporate certifications including ISO 9001, API, ASME, DNV, Gos-Standard and Gosgortechnadzor.
4.4 Personnel Resources: Brandt/EPI has established a reputation for professional, consistent, safe performance and innovative solutions to client needs. Our professionals are experienced in solid/liquid separations, site remediation, design engineering, petroleum geology, chemical processing, environmental law, and finance. This expertise provides the ability to offer a wide variety of products and services, a positive working environment, and the financial capabilities to develop long-term relationships with clients, suppliers, and sub-contractors. Brandt/EPI and its affiliated companies have over 400 operations and technical support personnel strategically located in local service centers throughout the world. Many personnel hold industry certifications in HAZWOPER, Process Safety, Offshore Operations, H2S, and CPR. Brandt/EPI also maintains a wide network of technical experts through participation in industry
organizations such as the American Petroleum Institute, Society of Petroleum Engineers, American Institute of Chemical Engineers, American Association of Drilling Engineers, International Association of Drilling Contractors, National Utility Contractors Association, and others.
PRODUCTS AND SERVICES Brandt/EPI specializes in field-proven separation systems for a variety of applications. These include exploration and production, petrochemical, stone dewatering, pulp and paper, clay processing, and municipal sludge. High-performance screen separators, hydrocyclones, and centrifuges are available as separate units or as components of custom-designed systems. Brandt/EPI also provides quality replacement screen panels with a wide range of screen cloth for all screen units. Brandt/EPI provides a full range of site remediation services through our own operations and in partnership with Remediation Management, Services, Inc. We have successfully closed over 1,000 surface pits to Louisiana Rule 29-B standards or better in over eighteen years of site remediation.
system (-5° to +5°), and screen changes are quick with the exclusive screen latches. A singlemotor/sealed gearbox drive system reduce downtime and maintenance costs. The ATL-1000 is only 93” from end to end, but has a full 35.8 sq.ft. of screen area. Multiple units can be used to increase capacity. Figure 4-1 ATL-1000 Linear Motion Screen Separator
4.5 Linear Motion Screen Separators ATL-1000 Screen Separator The ATL-1000 combines a tandem screen arrangement and linear motion with a ramp-slope screen deck and flat Blue Hex SM screen panels (38-450 mesh) to maximize solids separation in a single, compact unit that routinely out-performs larger shakers. The flat (no crown) screen deck reduces liquid loss down the sides of the screens and maximizes usable screen area. The ramp-slope design allows the feed end screens to be operated downhill with the discharge end screens flat for maximum conveyance of sticky solids. With the feed end screens flat, the discharge end screens tilt uphill to improve cuttings dryness and increase capacity without the excessive pool depths found with other designs. Deck angle is easily adjusted with the pinned jacking
ATL-1200 Screen Separator Designed for smaller drilling rigs and workover units, the ATL-1200 combines the performance of the ATL-1000 Separator with a lower weir height in a single, compact unit that routinely out-performs larger shakers. The flat (no crown) screen deck reduces liquid loss down the sides of the screens and maximizes usable screen area. The ramp-slope design allows the feed end screens to be operated downhill with the discharge end screens flat for maximum conveyance of sticky solids. With the feed end
Figure 4-2 ATL-1200 Linear Motion Screen Separator
screens flat, the discharge end screens tilt uphill to improve cuttings dryness and increase capacity without the excessive pool depths found with other designs. Deck angle is easily adjusted with the pinned jacking system (-5° to +5°), and screen changes are quick with the exclusive screen latches. A single-motor/sealed gearbox drive system reduce downtime and maintenance costs. The ATL-1200 measures only 93” from end to end, but has a full 25.0 sq.ft. of screen area. Multiple units can be used to increase capacity.
other designs. The adjustable angle (+5° to -10°), 33.7 sq.ft. screen deck includes a unique dewatering screen panel and a small-footprint design. The dual Vibra-motor drive system is simple, efficient, and requires no maintenance. Multiple units may be used to increase capacity.
LCM-2D Screen Separator The LCM-2D Separator (patent pending) is designed for maximum screening efficiency from 30 to 250 mesh, higher process volumes, and minimum maintenance. The rampslope screen deck provides a horizontal feed screen and an inclined discharge screen for maximum solids separation without the excessive pool depths found on
Figure 4-3 LCM-2D Linear Motion Screen Separator
Figure 4-4 ATL-CS Cascade Screen Separator
Linear Motion Cascade Screen Separators ATL-CS Cascade Separator The ATL-CS is designed to screen fine, sticky clays at high flowrates in a single, modular unit. Typically constructed from corrosion-resistant stainless-steel, the ATL-CS combines the fine screening ability of a single-deck ATL-1200 with the circular motion of the proven Tandem Screen Separator into a unit with the lowest weir height of any highperformance cascade separator.
The ATL-CS provides a total of 65 sq.ft. of screen area and uses rugged hook-strip screens on the scalping decks and Blue Hex SM screen panels on the lower deck to improve efficiency and reduce screen costs. Multiple units may be used to increase capacity. If desired, combination stainless/carbon steel or full carbon steel construction are available.
Figure 4-5 LCM-2D Cascade Linear Motion Screen Separator
LCM-2D Cascade Separator The LCM-2D Cascade (patent pending) combines the fine screening ability and simplicity of the LCM-2D with a circular motion scalping shaker to screen fine, sticky clays at high flowrates in a single, modular unit. The LCM-2D Cascade uses the same screens on the upper scalping deck and the lower linear unit to reduce screen inventories and costs. Total screen
area is 56.3 sq.ft. Multiple units may be used to increase capacity.
Linear Motion Drying Shakers ATL Drying Shaker The ATL Drying Shaker is a compact “low-G” drying shaker. The ATL Dryer has proved to be superior to larger, “high-G” designs due to longer retention time on the screen surface and less liquid retained on the cuttings. The lower “G” forces also cause significantly less particle size degradation of the cuttings. Cuttings and fluids from the primary rig shakers are fine screened by an adjustable linear screen deck resulting in drier solids and cleaner reclaimed base mud. The recovered fluid is captured in an agitated tank and is returned to the active system by an integral centrifugal pump. Pump operations are automatic and controlled by a float valve switch mechanism. If desired, the recovered fluid may be centrifuged before it is returned to the active system.
Figure 4-6 ATL Drying Shaker
Conditioners may be configured as a two-stage separator with either desander or desilter cones only, or as a three-stage separator with both desander and desilter cones to provide up to 1500 GPM process capacity in a single unit. The most popular models are described here; other configurations are also available.
ATL-16/2 Mud Conditioner Figure 4-7 SDW-25 Drying Shaker
SDW-25 Drying Shaker In cases where additional screen area or higher G-forces are desired, the SDW-25 Dryer provides screening to 500 mesh. The SDW-25 is a four-panel version of the proven family of ATL linear motion separators, and has 33.3 sq.ft. of screen area. Deck angle is easily adjusted with a hydraulic jacking system. The independent dual-motor drive system eliminates pulleys, belts, or gearboxes to simplify operation and maintenance.
The ATL-16/2 Mud Conditioner is a three-stage separator rated at 1000 GPM. The ATL-16/2 has two desander cones and sixteen desilter cones mounted over an ATL-1200 linear motion screen deck. Two separate feed pumps are used to provide proper fluid processing through the cones. The cone underflow from both the desander and desilter may be processed through a fine mesh, 120-325 mesh, screen to remove fine solids and minimize
Linear Motion Mud Conditioners Mud Conditioners combine the fine screening ability and small footprint of Brandt/EPI’s linear motion separators with Brandt/EPI’s proven hydrocyclone separators to remove fine solids from weighted muds and to minimize waste volumes from unweighted muds. Mud 4.6
Figure 4-8 ATL-16/2 Mud Conditioner
liquid waste volume. If desired, the cone underflow may be discarded directly to waste. Total screen area is 25.0 sq.ft.
ATL-2800 Mud Conditioner The ATL-2800 Mud Conditioner is a two-stage separator rated at 1680 GPM. The ATL-2800 has twentyeight desilter cones mounted over an ATL-1200 linear motion screen deck. A centrifugal feed pump is
Figure 4-9 ATL-2800 Mud Conditioner
Figure 4-10 LCM-2D Mud Conditioner
LCM-2D Mud Conditioner The LCM-2D Mud Conditioner combines the fine screening ability and simplicity of the LCM-2D linear motion separator (patent pending) with Brandt/EPI’s proven hydrocyclone separators to remove fine solids from weighted muds and to minimize waste volumes from unweighted muds. The LCM-2D Mud Conditioner may be configured with desander and/or desilter hydrocyclones to provide either two- or three-stage separations up to 1680 GPM in a single unit. Total screen area is 33.7 sq.ft.
4.6 Orbital Screen Separators used to provide proper fluid processing through the cones. The cone underflow may be processed through a fine mesh, 120-325 mesh ,screen to remove fine solids and minimize liquid waste volume. If desired, the cone underflow may be discarded directly to waste. Total screen area is 25.0 sq.ft.
Tandem Screen Separator The dual-deck Tandem Screen Separator is designed to process high volumes between 20 and 120 mesh. The horizontal screen deck and circular motion provide excellent conveyance of solids, especially sticky clays. High capaci-
Figure 4-11 Tandem Screen Separator
ty and efficient separation are achieved because the top screen separates large solids from the mud and improves the separating performance and screen life of the bottom screen. The reliability, low maintenance requirements and quiet, dependable operation have made these machines industry standards for over 20 years. Tandem Separators are available in single, dual, and triple units. Junior units are available for workover and similar operations.
low to moderate capacities of materials requiring coarse screen separations, 30 to 50 mesh or larger. A rugged, single motor design is combined with unbalanced, elliptical motion to provide years of trouble-free operation. The standard separator may also be used as a scalping shaker to reduce equipment costs. Standard Separators are available in single, dual, and triple units. Junior units are available for workover and similar operations.
Mud Cleaners Brandt/EPI Mud Cleaners are a field-proven, two-stage separator designed to process up to 600 GPM over a single basket. Their horizontal screen deck and circular motion provide excellent conveyance of solids, especially sticky clays. The reliability, low maintenance require-
Figure 4-12 Standard Screen Separator
Standard Screen Separator The single-screen Standard Separator is designed to process
Figure 4-13 Mud Cleaners
ments and quiet, dependable operation have made these machines industry standards for over 20 years. Mud Cleaners are available in single or dual units and with one or two pre-tensioned (PT) screen decks. Mud Cleaners are available with 10, 12, 16, or 20 Desilter Cones.
4.7 Screen Panels Blue HexSM Screen Panels Brandt/EPI’s exclusive Blue Hex screen panels are flat — there is no crown. This design increases usable screen area and reduces liquid loss along the sides of screen panels. Blue HexSM screen panels eliminate the leading SM
Figure 4-14 Blue HexSM Screen Panels
causes of screen failures — screen flex, propagation of tears, improper tensioning, blinding and contamination from process fluids. Blue HexSM screens are available in single- and multi-layer configurations. The wirecloth is factory pre-tensioned for longer screen life. These screens use a rigid support frame and grid to eliminate screen flex and sag. The result is longer screen life and
more efficient solids separation. The support grid also prevents small tears from spreading across the entire screen surface. When a tear does occur, it can be easily repaired with Brandt/EPI’s exclusive screen plugs. Finally, the bonding process results in a screen panel that is impervious to degradation from high temperatures, chemicals, or oils.
Pinnacle™ Three-dimensional Screen Panels* Pinnacle™ screen panels offer up to 40% more screening area without increasing the overall size of the screen panel or adding additional shakers. This concept, similar to the design of a pleated air filter has several advantages: • Provides even distribution of fluid across the screen surface • Eliminates unwanted fluid loss near the screen edges • Improves dryness of solids discharge • Allows the use of finer screens, usually 2–3 mesh sizes finer The increased usable screen area of Pinnacle™ screens is best utilized when combined with flat screen panels on linear motion shaker with an uphill basket slope. Pinnacle™ screens may also improve performance on scalping shakers and other orbital shakers 4.9
when used in offshore (floater) applications to reduce the effects of swell and heave. Pinnacle™ screen panels are available for most popular fine screen shakers in several combinations of screen layers and mesh size, from 84 mesh to 250 mesh. * Pinnacle is a trademark of Advanced Wirecloth, Inc.
PT Screen Panels PT screen panels are used on Brandt/EPI™ Mud Cleaners. This two-panel screen consists of one or more layers of fine-mesh screen cloth, pretensioned and bonded to a metal frame for strength and long screen life. PT screens are available from 80 mesh to 325 mesh, in market grade and tensile bolting cloths.
4.8 Hydrocyclone Units Desanders Available in 500 GPM, 1000 GPM, and 1500 GPM models, Brandt/EPI™ Desanders offer excellent high temperature tolerance, resistance to abrasion, and low-cost replacement. They incorporate superior involute feed entry, preferred flanged design for tight, leak-proof performance, all-polymer construction, and standard Victaulic® connections. These features make them a popular choice for retrofit of existing units. Each desander cone is 12” diameter with a 2-1/8” diameter, fixed solids discharge apex for maximum solids removal. 1-3/4” and 1-1/2” apex sizes are also available. For extremely abrasive conditions, a molded-in ceramic insert may be specified.
Hook-Strip Screen Panels Brandt/EPI™ also supplies a full line of hook-strip screens available in single-layer or multi-layer configurations. Hook-strip screen panels are available from 8-mesh to 500mesh, and may be manufactured from square-mesh market grade or tensile bolting cloths, proprietary oblong or rectangular weaves, and the latest, high-conductance weaves for special applications. Urethane screens, equivalent to 50-140 mesh cloths are also available. 4.10
Figure 4-15 Desander
Desilters Available to process 60 gpm to 1440 gpm, Brandt/EPI™ Desilters offer excellent high temperature tolerance, resistance to abrasion, and low-cost replacement. They incorporate involute feed entry, preferred flanged designs for tight, leak-proof performance, all-polymer construction, and standard Victaulic® connections. These features make them the preferred choice for both contractors and operators. Each desilter cone is 4” diameter with an adjustable solids discharge apex for maximum solids removal. All desilter cones have a molded-in ceramic insert to reduce wear and extend the life of the cone.
Figure 4-16 Desilter
Figure 4-18 Decanting Centrifuge
4.9 Centrifuges Brandt/EPI™ offers several models of reliable, high-performance centrifuges to meet your two-phase liquid/solid separation requirements — fine solids removal from unweighted muds, viscosity control (barite recovery) for weighted muds, and dual centrifuge systems for synthetic oil base muds and other critical applications. All Brandt/EPI™ decanting centrifuges can be used in both unweighted and weighted mud applications. All units feature high capacity contour bowls, hard-faced conveyor feed ports and scroll flight tips, hardfaced solids discharge ports, and variable pond depth orifices. For safe operation, all units include safety shut-down devices, explosion-proof electrics, and heavy-duty guards over all rotating components.
SC-1 Decanting Centrifuge Figure 4-17 Desilter Cone
The SC-1 centrifuge has an 18” x 28” bowl and is designed primarily for barite recovery from fluids 4.11
weighing up to 26 ppg. The SC-1 can also process up to 150 gpm of unweighted muds, removing up to 6 tons per hour (TPH) of low gravity solids.
SC-4 Decanting Centrifuge The SC-4 centrifuge has a 24” x 40” bowl and a double-lead conveyor designed for maximum solids tonnage removal (up to 8 TPH) and process rates up to 250 gpm for unweighted muds. The SC-4 is also an excellent dewatering centrifuge and barite recovery centrifuge due to its 59:1 gearbox. If desired, an electric back drive to vary conveyor/bowl speed ratio is available as an option.
designed for ultra fine solids removal from unweighted muds at process rates up to 160 GPM and 5 TPH. Top recommended bowl speed is 3250 RPM. Stainless steel construction and sintered tungsten carbide wear tiles provide years of trouble-free operation. The HS3400 is available in allelectric, hydraulic main drive, or all-hydraulic (main and back drive) configurations. The all-electric drive provides simple, reliable performance. The hydraulic drive systems offer additional separation versatility and flexibility to optimize solids/liquid separation over a wide variety of drilling conditions.
Figure 4-19 HS3400 Centrifuge with Electric Drive
HS3400 High Speed Decanting Centrifuge For applications that require high-speed, high G-force separations, the HS3400 decanting centrifuge has become the industry standard for high-speed performance and reliability. The HS3400 has a 14” x 49.5” bowl and is 4.12
Figure 4-20 HS3400 Centrifuge with Hydraulic Drive
SC-35HS Decanting Centrifuge The SC-35HS decanting centrifuge is designed for better high-speed performance, longer life, and less maintenance than competitive
Figure 4-21 SC-35HS Decanting Centrifuge
designs. Compared to other “highspeed designs, the SC-35HS centrifuge’s 15” x 48” contour bowl and the proprietary gearbox provide several advantages — higher “G-forces at a given speed, higher solids capacity (6 TPH), higher flowrates (up to 180 GPM), finer separations, and greater settling area in a smaller, more compact footprint. Top recommended speed is 3,500 RPM. Stainless steel construction and tungsten carbide wear tiles provide years of trouble-free operation. The SC-35HS is available in all-electric, hydraulic main drive, or all-hydraulic (main and back drive) configurations.
HS-5200 High Speed Decanting Centrifuge The HS5200 is a “third-generation” high-speed decanting centrifuge capable of 4000 Gs and 4200 RPM operation. Based on the proven HS3400 design, the HS5200 has a 16” x 49.5” contour bowl and high torque drive system for higher
capacity and sharper separations — up to 250 GPM and 8 TPH. The HS5200’s all-hydraulic drive system can be easily adjusted for optimum performance in all fluid processing conditions. Main bowl speed is infinitely variable up to the maximum 4200 RPM, and the bowl/ conveyor differential is also adjustable between 1 RPM and 100 RPM. Stainless steel construction and tungsten carbide wear tiles along the entire scroll length provide years of trouble-free operation.
Figure 4-23 HS-5200 High Speed Decanting Centrifuge
Roto-Sep Centrifuge The Roto-Sep Centrifuge is a perforated rotor design to remove undesirable fine solids from weighted drilling fluids. The rotating separation chamber increases solids settling rate to remove these fine solids and recover barite with up to 92% efficiency. Available in skid- or trailer-mounted units, the Roto-Sep provides slurrified solids, thus allowing the unit to be located a 4.13
Figure 4-24 Roto-Sep Centrifuge
distance away from the solids return tank and simplifying installation.
4.10 Dewatering Units Brandt/EPI offers several models of dewatering units, from simple, skid-mounted metering pump and tank modules, to the DWU-250 Dewatering Unit. The DWU-250 is a self-contained, portable system that includes all mixing and polymer aging tanks, metering pumps, piping and connection points, controls, and quality check points in a modular, weatherized container enclosure. The DWU-250 is used with one or more decanting centrifuges as part of the ChemicallyEnhanced Dewatering process. The DWU-250 may be equipped with
Figure 4-25 Self-contained DWU-250
Figure 4-26 Inside the DWU-250
climatized laboratory and office areas, including tropic or Arctic conditions.
4.11 Filtration Units The Brandt/EPI Super-Flo™ filtration system is a DE (diatomaceous earth) unit designed for clear filtrate quality, faster cycle times, and higher efficiency. The unique tubular elements provide maximum flow in minimum space; and the more effective pre-coat and cleaning cycles increase throughput and reduce downtime. The Super-Flo filtration unit is available in electric or diesel/pneumatic power models.
Figure 4-27 Filtration Unit
Figure 4-28 Vacuum Degasser
impeller blades for complete mixing action. Their low profile minimizes headroom requirements and provides stability and safety. Brandt/ EPI agitators use a single-reduction, worm/worm gear drive for higher efficiency, dependable service, and smooth vibration-free operation. The Agitator Sizing Chart for Drilling Muds, another Brandt/EPI innovation, simplifies proper agitator sizing and selection, and is located in Appendix D.
4.12 Vacuum Degassers The DG-5 (500 gpm) and DG-10 (1000 gpm) vacuum degassers have been rated by an independent study as the best-performing degassers for drilling fluid service. These degassers are compact, lowprofile, and provide maximum release and removal of entrained gas by flowing the gas-cut fluid in very thin sheets across a series of stacked plates. While an eductor jet removes the degassed mud, a rugged, H 2S-rated vacuum pump provides positive removal of gas. There is no remixing of mud and gas as found in other, low-efficiency methods. Interior parts are treated to resist corrosion.
4.13 Mud Agitators Brandt / EPI MA Series mechanical agitators are available from 3 HP to 25 HP, with flat or canted
Figure 4-29 Mud Agitator
4.14 Portable Rig Blowers Brandt/EPI developed these quiet, efficient blowers especially for improved comfort and safety on drilling rigs. Designed to meet applicable OSHA specifications, 4.15
4.15 Integrated Systems Closed Loop Processing Systems
Figure 4-30 Portable Rig Blower
these blowers are used to disperse potentially dangerous gasses and bothersome insects. Available in three sizes — 15,000 cfm, 25,000 cfm, and 40,000 cfm — Brandt/EPI Blowers move high volumes of air with minimal noise or vibration. To ensure safe operation, all blowers feature non-sparking aluminum blades, heavy-gauge safety guards and explosion-proof electrics. Blowers are available in floormounted, wall-mounted, or hangermounted units.
All Brandt / EPI™ equipment can be integrated into systems designed for specific applications. We have over 20 years’ experience designing, manufacturing, and operating systems for “Closed Loop” processing of drilling fluids, dewatering systems, cuttings wash systems, product classification systems, and other waste reduction/management systems. Brandt / EPI equipment is currently in service throughout the world, providing excellent results in land and offshore installations, remote areas, processing plants, in-plant installations, and site remediation projects. Brandt / EPI Closed Loop Mud Systems (CLMS) are customdesigned for your specific application, based on operational, environmental, and economic needs. A typical CLMS may include
Figure 4-31 Closed Loop Mud System
one or more primary Screen Separators, Drying Shakers, Mud Conditioner, and Decanting Centrifuge. Dual centrifuge installations for special applications — such as weighted oil base muds and synthetic oil- or water-base drilling fluids — are also readily available.
Coiled Tubing (CT) Processing Systems CT Processing Systems are designed for the specific requirements of coiled tubing operations, both drilling and workover. Their modular design makes it easy to select the total mud volume, type and number of fluid processing equipment, mixing equipment, and tank configuration. All compartments are mechanically agitated to prevent settling of weighting materials and maintain a homogenous fluid mixture. The integrated degasser (not shown) is specially designed to remove large amounts of entrained gas safely and effectively.
Trenchless Technology Processing Systems Brandt/EPI CLMS are also rapidly becoming the preferred choice for Trenchless Technology Mud Systems. We have successfully completed over 75 trenchless projects in North America, ranging from small diameter fiber-optic cable installations to large natural gas pipeline projects. We have also provided systems and operators for horizontal wells to neutralize underground contamination plumes and other environmental remediation projects.
Live Oil Systems Brandt/EPI offers a proprietary system to process three-phase solids/water/oil separations when drilling underbalanced through producing zones. The Brandt/EPI “Live Oil” System is a modular tank system, complete with pressure control and solids separation equipment. Water and oil are separated and recovered in separate tanks for future re-use or transportation.
4.16 Remediation Management Services
Figure 4-32 Coiled Tubing (CT) Processing System
Remediation Management Services, a Brandt/ EPI company, provides a full range of site remediation services throughout the world. In over eighteen years of site remediation, we have successfully closed over 1,000 surface pits to Louisiana 4.17
4.17 Technical and Engineering Services
Figure 4-33 Site Remediation Services
Rule 29-B standards or better. Techniques available include: • Closed loop mud systems • Chemically Enhanced Dewatering • Landfarming / landspreading • Bioremediation • Cuttings slurrification and injection systems • Sludge stabilization and fixation • Soil/sand washing • Surface pit closure • Waste minimization • Water treatment • Construction equipment • Pump rental • Water Discharge Permit No. 5259 Each service typically includes all necessary excavation equipment, process equipment, tanks, transfer pumps and related equipment, chemicals, power source, labor, onsite testing and analytical data, site closure, and necessary state or federal permits, reports, and other documentation.
Brandt/EPI™ offers a full range of technical and engineering services to ensure optimum application and performance of separation and other, related equipment. These services range from periodic, on-site inspections to complete design proposals and continuous on-site technical support, depending on project and client requirements. Technical and engineering services include: • Project pre-planning • Rig surveys • Project recommendations • On-site system operation and maintenance • Brandt’s exclusive RECAP™ Report (Removal Efficiency Cost Analysis Program) • CAD-based engineering • PC-based particle size analysis • Pilot testing • Technical education and training Any Brandt/EPI™ product may be custom-manufactured to meet your project requirements. All equipment can be supplied in full carbon steel, carbon/stainless steel combination, or full stainless steel in a variety of finishes and colors. Explosion-proof electrical components are standard, but other styles may be requested. Call your local Brandt/EPI representative for a quotation.
APPENDICES Glossary ..................................................................................................................A.2
Mud Solids Calculations Standard Calculations........................................................................................B.1 Field Calculations to Determine Total Solids Discharge.................................B.4 Field Calculations to Determine High and Low Gravity Solids Discharge ....B.5 Solids Control Performance Evaluation ...........................................................B.6 Method for Comparison of Cyclone Efficiency .............................................B.10
Mud Engineering Data Conversion Constants and Formulas ...............................................................C.1 Density of Common Materials..........................................................................C.2 Hole Capacities .................................................................................................C.3 Pounds per Hour Drilled Solids — Fast Rates ................................................C.4 Pounds per Hour Drilled Solids — Slow Rates...............................................C.5 Solids Content Chart .........................................................................................C.6
Equipment Selection Pre-well Project Checklist ................................................................................D.1 Screen Cloth Comparisons ...............................................................................D.2 Brandt/EPI™ Equipment Specifications ..........................................................D.3 Selecting Size and Number of Agitators ..........................................................D.7 Brandt/EPI™ Sales & Service Locations ..........................................................D.8
GLOSSARY LEGEND + API Bul 13C - API Bul D11 * IADC Mud Equipment Manual
A ADSORBED LIQUID The liquid film that adheres to the surfaces of solids particles which cannot be removed by draining, even centrifugal force. AERATION* The mechanical incorporation and dispersion of air into a drilling fluid system. If not selectively controlled, it can be very harmful.
ANTIFOAM A substance used to prevent foam by greatly increasing the surface tension. Compare: DEFOAMER. APERTURE + An opening. In a screen surface, the clear opening between wires. See related term: MESH. APEX See Preferred Term: UNDERFLOW OPENING.
AIR CUTTING See Preferred Term: AERATION
APEX VALVE See Preferred Term: UNDERFLOW OPENING.
AIR LOCK A condition causing a centrifugal pump to stop pumping due to a ball of air (or gas) in the impeller center that will not let liquid enter (usually caused by aeration).
API SAND Solids particles in a drilling fluid that are too large to pass through a U.S. Standard 200 Mesh Screen (74 micron openings). See related term: SAND CONTENT.
AMPLITUDE + The distance from the mean position to the point of maximum displacement. In the case of a vibrating screen with circular motion, amplitude would be the radius of the circle. In the case of straight-line motion or elliptical motion, amplitude would be one-half of the total movement of the major axis of the ellipse; thus one-half stroke. See related term: STROKE.
APPARENT VISCOSITY The viscosity a fluid appears to have on a given instrument at a stated rate of shear. It is a function of the plastic viscosity and the yield point. See also: VISCOSITY, PLASTIC VISCOSITY, and YIELD POINT.
AXIAL FLOW* Flow from a mechanical agitator in which the fluid first moves along the axis of the impeller shaft (usually down
toward the bottom of a tank) and them away from the impeller. B
That portion of a shale shaker containing the deck upon which the screen(s) is mounted; supported by vibration isolation members connected to the bed.
BACKPRESSURE + The pressure opposing flow from a solids separation device. See related term: DIFFERENTIAL PRESSURE.
BEACH Area between the liquid pool and the solids discharge ports in a decanting centrifuge or hydrocyclone.
BALANCE (as a Hydrocyclone)* To adjust a balanced design hydrocyclone so that it discharges only a slight drip of water at the underflow opening.
BED * Shale shaker support member consisting of mounting skid, or frame with or without bottom, flow diverters to direct screen underflow to either side of the skid and mountings for vibration isolation members.
BALANCE DESIGN (Hydrocyclone) A hydrocyclone designed so it can be operated to discharge solids when there are solids to separate, but will automatically minimize liquid discharge when there are no separable solids. BALANCE POINT * (of a Hydrocyclone) That adjustment at which exactly no liquid will discharge at the underflow opening, yet any greater opening at all would result in some liquid discharge. BARITE, BARYTES Natural barium sulfate, used for increasing the density of drilling fluids. The barite mineral occurs in many colors from white through grays, greens, and reds to black, according to the impurities. API standards require a minimum of 4.2 average specific gravity. BARREL (API) A unit of measure used in the petroleum industry consisting of 42 U.S. gallons. BASKET
BENTONITE A hydratable colloidal clay, largely made up of the mineral sodium montmorillonite, used in drilling fluids to create viscosity. See related term: GEL. BLADE See Preferred Term: FLUTE. BLINDING + A reduction of open area in a screening surface caused by coating or plugging. See related terms: COATING, PLUGGING. BLOWOUT An uncontrolled escape of drilling fluid, gas, oil, or water from the well caused by the formation pressure being greater than the hydrostatic head of the fluid in the hole. BOTTOM (Cyclone) See Preferred Term: UNDERFLOW OPENING. BOTTOM FLOODING The behavior of a hydrocyclone when
the underflow discharges whole mud rather than separated solids.
outward from the center of rotation. See related term: G-FORCE.
BOUND LIQUID See Preferred Term: ADSORBED LIQUID.
CENTRIFUGAL SEPARATOR + A general term applicable to any device using centrifugal force to shorten and/or to control the settling time required to separate a heavier mass from a lighter mass.
BOWL + The outer rotating chamber of a decanting centrifuge. C CAKE THICKNESS The measurement of the thickness of the filter cake deposited by a drilling fluid against a porous medium most often following the standard API filtration test. Cake thickness is usually reported in 32nds of an inch. See related term: WALL CAKE. CAPACITY The maximum volume rate at which a solids control device is designed to operate without detriment to separation. See related terms: FEED CAPACITY, SOLIDS DISCHARGE CAPACITY. CASCADE Fluid movement on a single deck, multiple screen sloping shale shaker basket which flow is parallel to screens. CAVING * Caving is a severe degree of sloughing. See related term: SLOUGHING. CENTIPOISE (cp) A unit of viscosity equal to 1 gram per centimeter-second. The viscosity of water at 20°C is 1.005 cp. CENTRIFUGAL FORCE + That force which tends to impel matter
CENTRIFUGAL PUMP A device for moving fluid by means of a rotating impeller which spins the fluid and creates centrifugal force. CENTRIFUGE A centrifugal separator, specifically: a device rotated by an external force for the purpose of separating materials of various specific gravities and/or particle sizes or shapes from a slurry to which the rotation is imparted primarily by rotating bowl. CERAMICS A general term for heat-hardened clay products which resist abrasion: used to extend the useful life of wear parts in pumps and cyclones. CHOKE * An opening, aperture, or orifice used to restrict a rate of flow or discharge. CIRCULATION The movement of drilling fluid from the suction pit through pump, drill pipe, bit, annular space in the hole, and back again to the suction pit. The time involved is usually referred to as circulation time. CIRCULATION RATE The volume flow rate of the circulation drilling fluid, usually expressed in gallons or barrels per minute.
CLAY-SIZE, CLAY (Particles) Any solids particles less than 2 microns in diameter. Natural clay particles are commonly (but not limited to) a hydrous silicate of alumina, formed by the decomposition of feldspar and other aluminum silicates. Clay minerals are essentially insoluble in water but disperse into extremely small particles as a result of hydra-small particles as a result of hydration, grinding, or velocity effects. COARSE (Solids) + Solids larger than 2000 microns in diameter. COATING A condition wherein undersize particles cover the openings of a screening surface by virtue of stickiness. See related term: BLINDING. COLLOIDAL (Solids) Particles so small that they do not settle out when suspended in a drilling fluid. Commonly used as a synonym for “clay.” CONE See Preferred Term: HYDROCYCLONE.
decanting centrifuge, a hollow hub with flutes designed to move the coarse solids out of the bowl. CROWN The curvature of a screen deck or the difference in elevation between its high and low points. CUT POINT A general term for the effectiveness of a liquid-solids separation device expressed as the particle size that is removed from the feed stream at a given percentage under specified operating conditions. See related term: MEDIAN CUT. CUTTINGS Small pieces of formation that are the result of the chipping and crushing action of the bit. Field practice is to call all solids removed by the shaker screen “cuttings,” in spite of the fact that such solids may include sloughed materials and may be smaller than the screen openings. CYCLONE See Preferred Term: HYDROCYCLONE. D
CONTAMINATION The presence in a drilling fluid of any foreign material that may tend to harm the desired properties of the drilling fluid.
DECANTING CENTRIFUGE + A centrifuge which continuously removes solids that are coarse enough to be separated from their free liquid.
CONTINUOUS PHASE The fluid phase of a drilling mud, either water or oil.
DECK The screening surface in a shale shaker basket.
CONVEYOR A mechanical device for moving material from one place to another. In a
DEFLOCCULATION Breakup of flocs of gel structures by use of a thinner or dispersant.
DEFOAMER Any substance used to reduce or eliminate foam by reducing the surface tension. Compare: ANTIFOAM. DEGASSER A device that removes entrained gas from a drilling fluid. DENSITY Matter measured as mass per unit of volume expressed in pounds per gallon (lbs/gal), pounds per square inch per thousand feet of depth (psi/1000 ft.), grams per liter (g/l), and specific gravity. Density is commonly referred to as “weight.” DESAND To remove the API sand from drilling fluid. DESANDER A hydrocyclone capable of removing the API sand (particles greater than 74 microns) from a drilling fluid. DESILT To remove most particles larger than 15-20 microns from a drilling fluid. DESILTER A hydrocyclone capable of removing most particles larger than 15-20 microns from a drilling fluid. DIFFERENTIAL PRESSURE (Hydrocyclone) The difference between the inlet and outlet pressures measured near the inlet and outlet openings of a hydrocyclone. DIFFERENTIAL PRESSURE (Wall) STICKING Sticking which occurs because part of the drill string (usually the drill collars)
becomes embedded in the filter cake, resulting in a non-uniform distribution of pressure around the circumference of the pipe. The conditions essential for sticking require a permeable formation and a pressure differential across the filter cake and drill string. DILUENT Liquid added to dilute or thin a drilling fluid. DILUTION Increasing the liquid content of a drilling fluid by addition of water or oil. DILUTION RATIO * Ratio of volume of dilution liquid to the volume of raw mud in the feed to a liquid-solids separator. DILUTION WATER Water used for dilution of water-base drilling mud. DIRECT-INDICATING VISCOMETER See VISCOMETER, DIRECT INDICATING. DISCHARGE SPOUT OR LIP Extension at the discharge area of a screen. It may be vibrating or stationary. DISPERSANT Any chemical which promotes dispersion of particles in a fluid. DISPERSE * To separate in component parts. Bentonite disperses by hydration into many smaller pieces. DISPERSION (of Aggregates)Disintegration of aggregates. Dispersion increases the specific surface are of solids resulting in an increase in viscosity and gel strength.
DIVIDED DECK + A deck having a screening surface longitudinally divided by partition(s). DOUBLE FLUTE + The flutes or leads advancing simultaneously at the same angle and 180° apart. DRILLED SOLIDS Formation particles drilled up by the bit. See related term: LOW SPECIFIC GRAVITY SOLIDS. DRILLING IN The operation during the drilling procedures at the point of drilling into the producing formation. DRILLING MUD OR FLUID A circulating fluid used in rotary drilling to carry cuttings out of the hole and perform other functions required in the drilling operation. See related term: MUD. DRILLING OUT The operation during the drilling procedure when cement is drilled out of the casing before further hole is made or completion attempted. DRILLING RATE The rate at which hole depth progresses, expressed in linear units per unit of time (including connections) as feet/minute or feet/hour. See related term: PENETRATION RATE. DRY BOTTOM Referring to a hydrocyclone, an adjustment of the underflow opening that causes a dry beach, usually resulting in severe plugging. DRY PLUG The plugging of the underflow opening
of a hydrocyclone caused by operating with a dry bottom. DYNAMIC The state of being active or in motion; opposed to static. E EDUCTOR A device using a high velocity jet to create a vacuum which draws in liquid or dry material to be blended with drilling mud. EFFECTIVE SCREENING AREA The portion of a screen surface available for solids separation. EFFLUENT See Preferred Term: OVERFLOW. ELASTOMER Any rubber or rubber-like material (such as polyurethane). ELEVATION HEAD The pressure created by a given height of fluid. See related term: HEAD. EMULSIFIER or EMULSIFYING AGENT A substance used to produce an emulsion of two liquids which ordinarily would not mix. EMULSION A substantially permanent mixture of two or more liquids which do not normally dissolve in each other. They may be oil-in-water or water-in-oil types. EQUIVALENT SPHERICAL DIAMETER (ESD) + The theoretical dimension usually referred to when the sizes of irregularly shaped small particles are discussed.
These dimensions can be determined by several methods, such as: settling velocity, electrical resistance, and light reflection. See related term: PARTICLE SIZE. F FEED, or FEED SLURRY A mixture of solids and liquid entering a liquid-solids separation device, including dilution liquid if used. FEED CAPACITY * The maximum feed rate that a solids separation device can effectively handle, dependent upon particle size, particle concentration, viscosity, and other variables. See related terms: CAPACITY, SOLIDS DISCHARGE CAPACITY. FEED CHAMBER + The part of a device which receives the mixture of diluents, mud and solids to be separated. FEED HEAD The pressure (expressed in feet of head) exerted by the drilling fluid in a header. See related term: HEAD. FEED HEADER + A pipe, tube, or conduit to which two or more hydrocyclones are connected and from which they receive their feed slurry. FEED OPENING See Preferred Term: INLET. FEED PRESSURE + The actual gauge pressure measured as near as possible to, and upstream of, the inlet of a device.
FILTER CAKE The suspended solids that are deposited on a porous medium during the process of filtration, such as the standard API fluid loss test. It may also refer to the solids deposited on the wall of the hole. See related term: WALL CAKE. FILTER CAKE THICKNESS A measurement of the solids deposited on filter paper in 32nds of an inch during the standard 30-min. API filter test. This term also refers to the cake deposited on the wall of a hole. FILTER PRESS A device for determining fluid loss of a drilling fluid. FILTRATION The process of separating suspended solids from their liquid by forcing the latter through a porous medium. Two types of fluid filtration occur in a well: dynamic filtration while circulating, and static filtration when at rest. FILTRATION RATE See FLUID LOSS. FINE (Solids) + Particles whose diameter is between 44-74 microns. FINE SCREEN SHAKER A vibrating screening device designed for screening drilling fluids through screen cloth finer than 40 mesh. FISHING Operations on the rig for the purpose of retrieving sections of pipe, collars, junk, or other obstructive items which are in the hole and would interfere with drilling.
FLIGHT + On a decanting centrifuge, one full turn of a spiral helix, such as a flute or blade of a screw-type conveyor. FLOCCULATING AGENT A substance, such as most electrolytes and certain polymers, that causes flocculation. FLOCCULATION Loose association of particles in lightly bonded groups, or non-parallel association of clay platelets. In drilling fluids, flocculation results in thickening gelation. FLOODING The effect created when a screen or centrifuge is fed beyond its capacity. Flooding may also occur on a screen as a result of blinding. FLUID LOSS Measure of the relative amount of fluid loss (filtrate) through permeable formations or membranes when the drilling fluid is subjected to a pressure differential. For standard API filtration-test procedure, see API RP 13B. FLUTE The curved metal blade wrapped around a shaft as on a screw conveyor in a centrifuge. FOAM A light frothy mass of fine bubbles formed in or on the surface of a liquid; usually caused by entrained air or gas. FORMATION DAMAGE Damage to the productivity of a well resulting from invasion into the formation by mud particles or mud filtrate.
FREE LIQUID The layer of liquid that surrounds each separate particle in the underflow of a hydrocyclone. The thickness of this film depends upon the cyclone and the viscosity of the fluid. FUNNEL VISCOSITY The time, in seconds, for a quart (or liter) of drilling mud to flow out the bottom of a Marsh Funnel. Used in the field as a rough measure of apparent viscosity. See related terms: MARSH FUNNEL, APPARENT VISCOSITY. G GAS-CUT (Mud) Drilling fluid containing entrained gas. GEAR RATIO + On a decanting centrifuge, the ratio of the outer bowl speed to the difference in speed between the outer bowl and the screw conveyor, normally expressed as the number of revolutions of the outer bowl for a given difference of one complete revolution between the outer bowl and the screw conveyor. GEAR UNIT + On a centrifuge, a reduction device connected to the rotating bowl and driving the conveyor at a slightly different rate. GEL A term used to designate high colloidal, high-yielding, viscosity-building commercial clays, such as bentonite and attapulgite clays. GEL STRENGTH The ability or the measure of the ability of a colloid to form gels. Gel strength
is a pressure unit usually reported in lbs/100 sq. ft. It is a measure of the same interparticle forces of a fluid as determined by the yield point under dynamic conditions. GEL STRENGTH, INITIAL The measured initial gel strength of a fluid is the maximum reading (deflection) taken from a direct-reading viscometer after the fluid has been allowed to sit for 10 minutes.
HOOK STRIPS + The hooks on the edges of a screen section which accept the tension member. HOPPER See MUD HOPPER. HORSEPOWER A measure of the rate at which work is done. Motor nameplate horsepower is the maximum steady load that the motor can pull without damage.
G-FORCE * The acceleration of gravity (32.2 ft/sec/sec, 9.8 m/sec/sec). Multiplied acceleration due to centrifugal force is usually expressed as 1G, 2G, 3G, 11,000G etc.
HYDRATION The act of a substance to take up water by means of absorption and/or adsorption; usually results in swelling, dispersion and disintegration into colloidal particles.
GUMBO * Any relatively sticky shale formation encountered while drilling.
HYDROCYCLONE A liquid-solids separation device which utilizes centrifugal force to speed up settling. Drilling fluid is pumped tangentially into a cone and the rotation of the fluid provides centrifugal force to separate particles by mass weight - the heavier solids being separated from the light solids and liquid.
GUNNING THE PITS Agitation of the drilling fluid by means of mud guns. H HEAD The height (in feet) of a column of fluid necessary to develop a specific pressure. Commonly used to refer to the pressure put out by a centrifugal pump. HIGH SPECIFIC GRAVITY SOLIDS Solids whose specific gravity is greater than 4.2 which are added to a drilling fluid specifically to increase mud density. Barite is the most common, but others such as iron oxides are also used. See related Term: LOW SPECIFIC GRAVITY SOLIDS.
HYDROCYCLONE SIZE * The maximum inside working diameter of the cone part of a hydrocyclone. I INERTIA * That force which makes a moving particle tend to maintain its same direction. INHIBITED MUD A drilling fluid having a aqueous phase with a chemical composition that tends to retard and even prevent (inhibit) appreciable hydration (swelling) or dis-
persion of formation clays and shales through chemical and/or physical means. See INHIBITOR (mud).
LIQUID * Fluid that will flow freely, takes the shape of its container.
INHIBITOR (mud) Substances generally regarded as drilling mud contaminants, such as salt and calcium sulfate, are called inhibitors when purposely added to mud so that the filtrate from the drilling fluid will prevent or retard the hydration of formation clays and shales.
LIQUID-CLAY PHASE See Preferred Term: OVERFLOW
INLET The opening through which the feed mud enters a solids control device. INTERMEDIATE (Solids) + Particles whose diameter is between 250-2000 microns. INVERT OIL-EMULSION MUD An invert emulsion is a water-in-oil emulsion where fresh or salt water is the dispersed phase and diesel, crude, or some other oil is the continuous phase. Water increases the viscosity and oil reduces the viscosity. L LEAD In a decanting centrifuge, the slurry conducting channel formed by the adjacent walls of the flutes or blades of the screw conveyor. LIGNOSULFONATES Organic drilling fluid additives derived from by-products of sulfite paper manufacturing process from coniferous woods. Commonly used as dispersants and anti-flocculants. In large quantities, may be used for fluid-loss control and the shale inhibition.
LIQUID DISCHARGE See Preferred Terms: OVERFLOW (Hydrocyclones); UNDERFLOW (screens). LIQUID FILM The liquid surrounding each particle discharging from the solids discharge of cyclones and screens. See related term: FREE LIQUID. LOST CIRCULATION The result of whole mud escaping into a formation, usually in cavernous, fissured, or coarsely permeable beds, evidenced by the complete or partial failure of the mud to return to the surface as it is being circulated in the hole. LOST CIRCULATION MATERIALS (LCM) Materials added to drilling fluid to control mud loss by bridging or plugging the lost circulation zone. LOW SILT MUD An unweighted mud that has all the sand and high proportion of the silts removed and has a substantial content of bentonite or other water-loss-reducing clays. LOW SOLIDS MUDS Low solids muds are unweighted water-base muds containing less than 10% drilled solids (1-4% is a normal range). They are used whenever it is desirable to increase penetration rate. A.11
In general, the lower solids content in a mud, the faster a bit can drill. LOW SPECIFIC GRAVITY SOLIDS Drilled solids of various sizes, commercial colloids, salts, lost circulation materials, i.e., all solids in drilling fluid, except barite or other commercial weighting materials. Typical S.G. is 2.6. M MANIFOLD (Cyclone) A piping arrangement through which liquids, solids or slurries from one or more sources can be fed to or discharged from a solids separation device. MARSH FUNNEL An instrument used in the field to determine funnel viscosity of a drilling fluid. See related term: FUNNEL VISCOSITY. MASS The effective weight of a particle, considering both its specific gravity and particle size. MECHANICAL AGITATOR A device used to mix, blend, or stir fluids by means of a rotating impeller blade. MEDIAN CUT * In separating solids particles from a specific liquid-solids slurry under specified conditions, the effectiveness of the separation device expressed as the particle size that reports 50% to the overflow and 50% to the underflow. MEDIUM (solids) + Particles whose diameter is between 74-250 microns.
MESH The number openings per linear inch in a screen. For example, a 200 mesh screen has 200 openings per linear inch. MESH COUNT The count is the term most often used to describe a square or rectangular mesh screen cloth. A mesh count such as 30 x 30 (or often 30 mesh) indicates a square mesh, while a designation such as 70 x 30 mesh indicates a rectangular mesh. MESH EQUIVALENT As used in oilfield drilling applications, the U.S. Sieve number which has the same size opening as the minimum opening of the screen in use. MICRON (µ) A unit of length equal to one thousandth of a millimeter; used as a measure of particle size. MUD Mud is the term most commonly given to drilling fluids; used for circulating out cuttings and many other functions while drilling a well. MUD ADDITIVE Any material added to a drilling fluid to achieve a particular purpose. MUD BALANCE A beam-type balance used in determining mud density. It consists primarily of a base, graduated beam with constantvolume cup, lid, rider, knife edge and counterweight. MUD BOX The feed compartment on a shale shaker into which the mud flow line
discharges, and from which the mud is either fed to the screens or is bypassed. Also called Backtank or Possum Belly. MUD CLEANER A solids separation device which combines several manifolded hydrocyclones and a fine mesh vibrating screen to remove valuable mud additives and liquids to the active mud system. MUD CONE See Preferred Term: HYDROCYCLONE. MUD ENGINEER One versed in drilling fluids whose duties are to manage, implement, and maintain the various types of oilwell mud programs.
solids to the mud is by means of the mud hopper. Some other devices for mixing are: eductors, mechanical agitators, electric stirrers, mud guns, and chemical barrels. MUD PIT Earthen or steel storage facilities for the surface mud system. Mud pits which vary in volume and number are of two types: circulating and reserve. Mud testing and conditioning is normally done in the circulating pit system. MUD PUMPS See RIG PUMPS. MUD SCALES See MUD BALANCE.
MUD FEED + Drilling fluid, with or without dilution, for introduction into a liquid-solids separator.
MUD STILL See RETORT.
MUD GUNS A system of pumps and piping in which drilling mud is pumped through nozzles at a high velocity. Used for mixing, blending and stirring the mud pits.
NEAR SIZE The material very nearly the size of a screen opening, generally considered as plus or minus 25% of the opening.
MUD HOPPER * A device used for mixing mud chemicals and other products into a fluid stream. It usually consists of a mud jet, an open top hopper, and downstream venturi.
OBLONG (Mesh) Screen cloth having more wires per inch in one direction than in another. For example, 70 x 30 mesh has 70 wires per inch in one direction and 30 wires per inch in the other direction. (Also called “rectangular” mesh.)
MUD HOUSE A structure at the rig to store and shelter sacked materials used in drilling fluids. MUD MIXING DEVICES The most common device for adding
OIL-BASE MUD A drilling fluid containing oil as its liquid phase, usually including 1-5% water emulsified into the system.
OPEN AREA See PERCENT OPEN AREA. OVERFLOW The discharge stream from a centrifugal separation device that contains a higher percentage of liquids than does the feed. OVERFLOW HEADER * In hydrocyclone operation, a pipe into which two or more hydrocyclones discharge their overflow. OVERLOAD + To feed separable solids to a separating device at a rate greater than its solids discharge capacity. OVERSIZE (Solids) Particles, in a given situation, that can be separated from the liquid phase by centrifugal force or which will not pass through the openings of the screen in use. P PARTICLE In drilling mud work, a small piece of solid material. PARTICLE SIZE Particle diameter, usually expressed in microns. See related term: EQUIVALENT SPHERICAL DIAMETER.
trates the formation, expressed in linear units, i.e., feet/minute or feet/hour. See related term: DRILLING RATE. PERCENT OPEN AREA Ratio of the area of the screen openings to the total area of the screen surface. PERFORATED CYLINDER CENTRIFUGE + A mechanical centrifugal separator in which the rotating element is a perforated cylinder (the rotor) inside of and concentric with an outer stationary cylindrical case. PERFORATED ROTOR + The rotating inner cylinder of the perforated cylinder centrifuge. PERMEABILITY Normal permeability is a measure of the ability of a formation to allow passage of a fluid. PLASTICITY The property possessed by some solids, particularly clays and clay slurries, of changing shape or flowing under applied stress without developing shear planes or fractures; that is, it deforms without breaking.
PARTICLE SURFACE AREA See SPECIFIC SURFACE AREA.
PLASTIC VISCOSITY Plastic viscosity is a measure of the internal resistance to fluid flow attributable to the amount, type, and size of solids present in a given fluid. When using a direct-indicating viscometer, plastic viscosity is found by subtracting the 300-rpm reading from the 600-rpm reading.
PENETRATION RATE The rate at which the drill bit pene-
PLUGGING (Screen Surface) The wedging or jamming of openings
PARTICLE SIZE DISTRIBUTION + The fraction or percentage of particles of various sizes or size ranges. See related term: SIEVE ANALYSIS.
in a screening surface by particles, preventing passage of undersize material. See related term: BLINDING. POLYMER A synthetic mud additive used to maintain viscosity, control fluid loss and maintain other desirable mud properties. POLYURETHANE A high performance elastomer polymer used in construction of hydrocyclones for its unique combination of physical properties, especially abrasion, toughness and resiliency. POOL The reservoir or pond of fluid, or slurry, formed inside the wall of hydrocyclones and centrifuges and in which classification or separation of solids occurs due to the settling effect of centrifugal force. PORTS + The openings in a centrifuge for entry or exit of materials. Usually applied in connection with a descriptive term, i.e., feed ports, overflow ports, etc. PRESSURE HEAD * Pressure within a system equal to the pressure exerted by an equivalent height of fluid (expressed in feet). See related term: HEAD. R RADIAL FLOW * Flow from a mechanical agitator in which fluid moves away from the axis of the impeller shaft (usually horizontally toward a mud tank wall). RATE OF PENETRATION See PENETRATION RATE.
RAW MUD Mud, before dilution, that is to be processed by solids removal equipment. RECTANGULAR OPENING (Screen Cloth) See OBLONG MESH. RETENTION TIME (Screen) + The time any given particle of material is actually on a screening surface. RETENTION TIME + (Centrifugal Separators) The time the liquid phase is actually in the separating device. RETORT An instrument used to distill oil, water, and other volatile material in a mud to determine oil, water, and total solids content in volume-percent. Also called “mud still”. RHEOLOGY The science that deals with deformation and flow of matter. RIG PUMPS (or Mud Pumps) The reciprocating, positive displacement, high pressure pumps used to circulate drilling fluid through the hole. RIG SHAKER A general term for a shale shaker using coarse mesh screen. ROPE DISCHARGE The characteristic underflow of a hydrocyclone operating inefficiently and so overloaded with separable solids that not all the separated solids can crowd out the underflow opening, causing those that can exit to form a slow-moving, heavy, rope-like stream. A.15
(Also referred to as “rope” or “rope underflow.”)
solids which may get past the shale shaker.
ROTARY DRILLING The method of drilling wells that depends on the rotation of a drill bit which is attached to a column of drill pipe. A fluid is circulated through the drill pipe to flush out cuttings and perform other functions.
SCREEN CLOTH A type of screening surface, woven in square or rectangular openings. See related term: WIRE CLOTH.
RPM * Revolutions per minute. S SALT-WATER MUDS A drilling fluid containing dissolved salt (brackish to saturated). These fluids may also include native solids, oil, and/or such commercial additives as clays, starch, etc. SAMPLES Cuttings obtained for geological information from the drilling fluid as it emerges from the hole. They are washed, dried, and labeled as to the depth. SAND CONTENT The sand content of a drilling fluid is the insoluble solids content retained on a 200-mesh screen. It is usually expressed as the percentage bulk volume of sand in a drilling fluid. This test is an elementary type in that the retained solids are not necessarily silica and may not be altogether abrasive. SAND TRAP The first compartment and the only unstirred compartment in a welldesigned mud system; intended as a settling compartment to catch large
SCREENING A mechanical process which accomplishes a separation of particles on the basis of size, through their acceptance or rejection by a screening surface. SCREENING SURFACE The medium containing the openings for passage of undersize material. SCROLL See Preferred Term: FLUTE. SETTLING VELOCITY The velocity a particle achieves in a given fluid when gravity forces equal the friction forces of the moving particle. SHALE Stone of widely varying hardness, color, and compaction that is formed of clay-sized grains. SHALE SHAKER A general term for devices which use a vibrating screen to remove cuttings and other large solids from drilling mud. SHEAR (Shearing Stress) An action, resulting from applied forces, which causes or tends to cause two contiguous parts of a body to slide relatively to each other in a direction parallel to their plane of contact - as in particles within a mud. SIEVE See Preferred Term: TESTING SIEVE.
SIEVE ANALYSIS A measurement of particle size and percentage of the amount of material in various particle size groupings. See related term: PARTICLE SIZE DISTRIBUTION. SILT Materials whose particle size generally falls between 2 microns and 74 microns. A certain portion of dispersed clays and barite falls into this particle size range as well as drilled solids. SIZE DISTRIBUTION See Preferred Term: PARTICLE SIZE DISTRIBUTION. SLOUGHING A situation in which portions of a formation fall away from the walls of a hole, as a result of incompetent unconsolidated formations, high angle of repose, wetting along internal bedding planes, or swelling of formations caused by fluid loss. See related term: CAVING. SLURRY A mixture or suspension of solid particles in one or more liquids. SOLIDS + All particles of matter in the drilling fluid, i.e., drilled formation cuttings, barite, etc. SOLIDS CONTENT The total amount of solids in a drilling fluid as determined by distillation, including both the dissolved and the suspended (or undissolved) solids. The suspended-solids content may be a combination of high and low specific gravity solids and native or commercial solids. Examples of dissolved solids are
the soluble salts of sodium, calcium, and magnesium. The total suspended and dissolved solids content is commonly expressed in percent by volume. SOLIDS DISCHARGE + That stream from a liquid-solids separator containing a higher percentage of solids than does the feed. SOLIDS DISCHARGE CAPACITY The maximum rate at which a liquidsolids separation device can discharge solids without overloading. SPECIFIC GRAVITY The weight of a particular volume of any substance compared to the weight of an equal volume of water at a reference temperature. SPECIFIC SURFACE AREA The effective surface area per unit of weight of some sample or grouping of particles of matter, usually expressed in units of area per units of weight such as square feet per pound, or acres per pound, square meters per gram, etc. It can be a valuable indicator of the amount of liquid certain particles can attract and retain on their surface. SPEED + The frequency at which a vibrating screen operates, usually expressed in RPM or CPM; the bowl rpm of a decanting centrifuge; the rotor rpm of a perforated cylinder centrifuge. SPRAY DISCHARGE The underflow of hydrocyclones when not overloaded with separable solids. SPUDDING IN The starting of the drilling operations of a new hole. A.17
SPUD MUD The fluid used when drilling starts at the surface, often a thick bentonite lime slurry.
TEST SIEVE A cylindrical or tray-like container with a screening surface bottom of standard aperture.
SPURT LOSS * The flux of fluids and solids which occurs in the initial stages of any filtration before pore openings are bridged and a filter cake is formed.
THINNER Any various organic agents (tannins, lignins, lignosulfonates, etc.) and inorganic agents (pyrophosphates, tetraphosphates, etc.) that are added to a drilling fluid to reduce the viscosity and/or thixotropic properties.
STROKE The distance between the extremities of motion; viz., the diameter of a circular motion. See related term: AMPLITUDE. STUCK A condition whereby the drill pipe, casing, or other devices inadvertently become lodged in the hole. SUMP A pit or tank into which a fluid drains before recirculation or in which wastes gather before disposal. SURGE LOSS See Preferred Term: SPURT LOSS. SWABBING When pipe is withdrawn from the hole in viscous mud or if the bit is balled, a low pressure is created below the bit.
THIXOTROPY The ability of a fluid to develop gel strength with time. That property of a fluid which causes it to build up a rigid or semirigid gel structure if allowed to stand at rest, yet can be returned to a fluid state by mechanical agitation. THRUST The force that pushes on the mud as on a shale shaker screen. TOTAL DEPTH (or TD) The greatest depth reached by the drill bit. TOTAL HEAD * The sum of all heads within a system (Total Head = velocity head + pressure head + elevation head.) U
T TENSIONING + The stretching of the screening surface within the vibrating frame. TENSION RING A rigid hoop surrounding a stretched screen cloth used for maintaining screen tension and mounting the screen to a shaker frame. A.18
ULTRA-FINE (Solids) + Particles whose diameter is between 244 microns. UNDERFLOW (Hydrocyclone) The discharge stream from centrifugal separators that contains a higher percentage of solids than does the feed. See general term: SOLIDS DISCHARGE.
UNDERFLOW (Screen) The discharge stream from a screening device which contains a greater percentage of liquids than does the feed. UNDERFLOW HEADER + A pipe, tube, or conduit into which two or more hydrocyclones discharge their underflow. UNDERSIZE (Solids) Particles that will, in a given situation, remain with the liquid phase when subjected to centrifugal force, or will pass through the openings of the screen in use. UNWEIGHTED (Mud) A drilling fluid which has not had significant amounts of high gravity solids added and whose density and whose density is generally less than 11 pounds per gallon. V VELOCITY HEAD * Head (relating to pressure when multiplied by the density of the fluid) created by the movement of a fluid, equal to an equivalent height of static fluid. VENTURI * Streamlining up to a given pipe size following a restriction (as in a jet in a mud hopper) to minimize turbulence and pressure drop. V.G. METER See VISCOMETER, DIRECT-INDICATING. VIBRATING SCREEN A screen with motion induced as an aid to solids separation.
VISCOMETER, DIRECT-INDICATING Commonly called a “V-G meter.” The instrument is a rotational-type device powered by means of an electric motor or handcrank, and is used to determine the apparent viscosity, plastic viscosity, yield point, and gel strengths of drilling fluids. The usual speeds are 600 and 300 rpm. See API RP 13B for operational procedures. VISCOSITY The internal resistance offered by a fluid to flow. This phenomenon is attributable to the attractions between molecules of a liquid, and is a measure of the combined effects of adhesion and cohesion to the effects of suspended particles, and to the liquid environment. The greater this resistance, the greater the viscosity. See related terms: APPARENT VISCOSITY, PLASTIC VISCOSITY. VORTEX + A cylindrical or conical shaped core of air or vapor lying along the central axis of the rotating slurry inside a hydrocyclone. VORTEX FINDER A hollow cylinder extending axially into the barrel of a hydrocyclone. The overflow exits from the separating chamber through the vortex finder, and the vortex is centered in the hydrocyclone by the hole in the vortex finder, hence the name. W WALL CAKE The solid material deposited along the wall of the hole resulting from filtration of the fluid part of the mud into the
formation. See related terms: CAKE THICKNESS, FILTER CAKE.
mud, usually by the addition of weight material.
WALL STICKING See Preferred Term: DIFFERENTIAL PRESSURE STICKING.
WETTING The adhesion of a liquid to the surface of a solid.
WATER-BASE MUD The conventional drilling fluid containing water as a the continuous phase.
WIRE CLOTH + Screen cloth of woven wire.
WATER FEED + Water to be added for dilution of the mud feed into a centrifugal separator. See related term: DILUTION WATER. WEIGHT (Mud Weight) In mud work, weight refers to the density of a drilling fluid. This is normally expressed in lbs/gal or specific gravity. See related term: DENSITY. WEIGHT MATERIAL Any of the heavy solids (specific gravity of 4.3 or more) used to increase the density of drilling fluids. This material is most commonly barite but can be galena, etc. In special applications, limestone is also called a weight material (even though its specific gravity is 2.6). WEIGHTED (Mud) A drilling fluid to which heavy (over 4.3 specific gravity) solids have been added to increase its density. WEIGHT UP * To increase the weight of a drilling
WORKOVER FLUID Any type of fluid used in the workover operation of a well. Y YIELD As applied to drilling mud, a term used to define the quality of a clay by describing the number of barrels of a given centipoise slurry that can be made from a ton of the clay. YIELD POINT The resistance to initial flow, representing the stress required to start fluid movement. This resistance is due to electrical charges located on or near the surfaces of the particles. The values of the yield point and thixotropy, respectively, are measurements of the same fluid properties under dynamic and static states. The Bingham yield value, reported in lbs/100 sq. ft, is determined by the direct-indicating viscometer by subtracting the plastic viscosity from the 300-rpm reading.
STANDARD CALCULATIONS I. MUD VOLUME • Capacity of annulus in bbl/ft = [(hole size)2 - (pipe OD)2] * 0.00097 • Approximate capacity of hole in bbl/1000 ft = (diameter of hole)2 • Approximate pipe displacement, bbl/100 ft = Weight of pipe (lb/ft) * 0.0364 • Pit volume in cu ft = Length * Width * Depth • Pit volume in bbl = cu ft 5.6 • Hole volume in bbl = [hole capacity(bpf) * depth(ft)] - pipe displacement (bbl) • Annular volume in bbl = hole volume - capacity and displacement of drill pipe • Total Volume = hole volume + pit volume II. CIRCULATION DATA • Pump output in bpm = bbl/stroke * strokes/minute • Annular velocity in fpm = pump output (bpm * 100) annular volume (bbl/100 ft) • Bottoms up in minutes = annular volume (bbl) pump output (bpm) • Hole cycle in minutes = pump output (bpm * 100) pump output (bpm) • Mud cycle in minutes = total volume (bbl) pump output (bpm)
SOLIDS DETERMINATION A. Low weight muds without barite • Percent solids by volume = (mud weight - water weight) * 7.5 • Correct for oil: For each 1% of oil, add 0.1 to % solids by volume • Correct for NaCl: For each 10,000 ppm salt, deduct 0.3% solids by volume. Ignore if salt content is less than 10,000 ppm. Convert Cl ppm to salt ppm (* 1.65) B. Weighted Muds • Percent by volume desired solids = (mud weight - 6) * 3.2 C. Drilled Solids Per Foot of Hole • Barrels per foot = (hole size + washout)2 * 0.00097 • Pounds per foot = bpf * 910.7
IV. SOLIDS CONTROL EVALUATION CALCULATIONS A.
Average specific gravity of solids in WBM 1. Freshwater muds Sa = (12 * Dm) - Vw Vs 2. Sa = (12 * Dm) - (Vwc * Sw) (100-Vwc)
Volume percent solids in freshwater muds, without weighting material Vs = 7.5 * (Dm - 8.34) OR 7.5 * (Dm - 62.55)
Volume percent solids in freshwater muds containing barite, S.G. = 4.2 Vb = (Sa - 2.6) * Vsc * 0.625 Vlg = Vsc - Vb
Volume percent solids in freshwater muds containing hematite, S.G. = 5.0 Vh = (Sa-2.6) * Vsc * 0.417 Vlg = Vsc - Vh
Volume percent in muds containing oil > 1% or salt > 10,000 ppm Vlg = [(Vw * Swc) + (Vo * So) + (Vsc * Shg)] - (100 * Sm) (Shg - Slg)
F. Bentonite and reactive clay correction CECa = 7.69 * (MBTm) Vlg Vben = Vlg * (CECa - CECds) (CECben - CECds)
Terms: CECa = Cation Exchange Capacity (CEC), average CECben = CEC of bentonite, typically 60 CECds = CE of drilled solids, typically 10 Cl = Total Chlorides, in mg/l Dm = Mud density, in ppg MBTm = Methylene Blue Test, in lbs/bbl Sa = Specific gravity of solids, average Shg = Specific gravity of high gravity solids Slg = Specific gravity of low gravity solids Sm = Specific gravity of mud So = Specific gravity of oil
Sw Swc Vb Vh Vhg Vlg Vs Vsc Vw Vwc
= Specific gravity of water = Specific gravity of water, corrected for chlorides = Volume percent barite (50% = 50, not .50) = Volume percent hematite = Volume percent high gravity solids = Volume percent low gravity solids = Volume percent total solids = Volume percent solids, corrected for chlorides = Volume percent water = Volume percent water, corrected for chlorides
Field Calculations to Determine Total Solids Discharge Note: This method is only a quick approximation of solids removal rate and should be used only for unweighted muds or where quick comparisons need to be made on a mud system to see what results when conditions change, i.e., is solids removal rate increasing, decreasing, or staying the same? 1.
Use a one-quart container and wristwatch to determine how many seconds (R) it takes to collect one quart of slurry from a cyclone underflow or a screen discharge.
Use a mud balance to obtain the density (D) of the slurry in pounds per gallon.
Use the following equations to calculate the rate of solids removed in pounds per hour. (D - 8.3) * 1450 = Total Solids Removed in #/hr R D = Density of slurry in #/gal. R = Rate of solids slurry discharge in sec/qt 8.3 = Density of Water
Example: D = 12.3 #/gal R = 8 sec (D - 8.3) * 1450 = R (12.3 - 8.3) * 1450 = 8 4 * 1450 = 725 #/hr 8
Field Calculations to Determine High and Low Gravity Solids Discharge 1.
Use a one-quart container and wristwatch to determine how many seconds (R) it takes for one quart of solids to be discharged.
Use a mud balance to obtain the density (D) of the sand slurry in pounds per gallon.
Retort the sand slurry to determine the volume fraction solids (Vs) and the volume fraction liquids (V1)
Use the following equations to calculate the rate of solids removed in pounds per hour. A. Total pounds per hour Solids Removed = [D - (8.34 * V1)] 900 R B. Average Specific Gravity of Solids = [D - (8.34 * V1)] (8.34 • Vs) C. Weight % Low Gravity Solids = 4.3 - ASG 1.6 D. Lbs/hr Low Gravity Solids = Total #/hr solids * weight % LGS E. Lbs/hr Barite = Total #/hr solids - #/hr LGS D = Density of solids slurry in #/gal R = Rate of removal in sec V1 = Volume fraction liquid Vs = Volume fraction solids ASG = Average Specific Gravity LSG = Low Gravity Solids
SOLIDS CONTROL PERFORMANCE EVALUATION There are several methods used to determine economic performance. This appendix describes a method to compare the cost of dilution versus mechanical removal. It utilizes the concept of a dilution factor (the amount of mud required to maintain a given solids concentration for every barrel of solids that remain in the mud) to determine dilution requirements. This method may be used to determine economic efficiency of any type of solids control equipment. Note: Effluent is defined as the process stream returned to the active mud system. The underflow is defined as the waste stream removed from the mud system and discarded.
Example: Given: Feed Rate Underflow Density Feed Density Effluent Density Total Low Gravity Solids Mud Cost Disposal Cost Equipment Cost per Day
= 30 gpm = 17.0 ppg = 10.0 ppg = 9.0 ppg = 6% = $15./bbl = $10./bbl = $600
Determine the economic performance.
Feed Rate, Vf = 30 gpm
Effluent Rate, Ve = ?
Feed Density, Df = 10.0 ppg
Effluent Density, De= 9.0
Underflow Rate, Vu = ? Underflow Density, Du = 17.0 ppg
1) Determine the Effluent and Underflow Volume Rates. 2) Calculate the Low Gravity Solids Removed per minute. 3) Calculate the equipment effectiveness & cost, compared to dilution 4) Calculate economic benefits
1) Determine the Effluent and Underflow Volume Rates. Df * Vf = (Du * Vu) + (De * Ve); & let X = Underflow Rate, Vu (10.0 * 30) = (17.0 * X) + [9.0 * (30-X)] = 300 = 17X + 270 - 9X 30/8 = X X
= 3.75 gallons per minute Underflow Rate Volume
(30 - X) = (30 - 3.75)
= 26.25 gallons per minute Effluent Rate Volume
Feed Rate, Vf = 30 gpm
Effluent Rate, Ve = 26.25
Feed Density, Df = 10.0 ppg
Effluent Density, De= 9.0
Underflow Rate, Vu = 3.75 Underflow Density, Du = 17.0 ppg
2) Calculate the Low Gravity Solids Removed per minute. a) Calculate the low gravity solids in the underflow: Let X = the decimal fraction low gravity solids 17/8.33 2.04 1.04 X
= X(2.6) + (1-X) = 2.6X + 1 - X = 1.6X = 1.04/1.6 = .65 or 65% solids in underflow
b) Calculate the low gravity solids removed: 3.75 * .65 = 2.44 gallons of low gravity solids removed per minute 3) Calculate the equipment effectiveness, compared to dilution a) Dilution: Assume the 9.0 ppg fluid is the desired fluid. It contains 5% solids. The equivalent dilution required to treat the solids removed is the volume removed divided by the desired fraction of solids. 2.44/.05 = 48.8 or 49 gallons per minute dilution required to match the machines effectiveness or (49 gal./min. * 60 min./hr.)/ 42 gal./bbl. = 70 bbls per hour equivalent dilution
Dilution Cost = Volume * (Mud Unit Cost + Disposal Unit Cost) Cost: $ = 70 * ($15 + $10) $1,750 per hour is Equivalent Dilution Cost
b) Mechanical Treatment Cost =[Liquid Volume Lost * (Mud Unit Cost + Disposal Unit Cost)] + Equipment Cost 3.75 X (1-.65) (1.3 X 60 min/hr)/ 42 gal/bbl
= 1.3 gallons of liquids removed per minute OR = 1.85 bbl/hr liquids removed
= [ 1.85 X ($15 + $10) ] + $600/24
= Cost to Remove the LGS
4) Calculate the economic benefits $
= (cost to remove) - (cost to dilute)
= $71.25 - $1,750
$ in ( ) = Savings, Removal compared to Dilution Therefore, in this example, prompt and continuous removal of drilled solids will save $1,679 per hour!
Method for Comparison of Cyclone Efficiency Assuming Identical:
Mud Feed Volume Feed Pressure
D V UF
= = =
Density Volume Rate Underflow
CASE #1: When DUF1 = DUF2
Then higher VUF = Greater Efficiency, since a greater volume of solids is being removed at the same liquid/solids ratio.
CASE #2: When VUF1 = VUF2
Then higher DUF = Greater Efficiency, since more solids (and less liquid) are being removed in the same underflow volume.
CASE #3: When one cone has higher DUF and higher VUF, then that cone is operating at significantly greater efficiency.
Note: When none of the above conditions occur, or for specific numerical accuracy, See Appendix A.
Conversion Constants and Formulas A.
Conversion Constants Specific Gravity (SG) Water ............................................1.0 1 Gallon of Water ............................................................8.34 lb 1 cu. ft. of Water..............................................................62.4 lb 1 Barrel (42 gallons) of Water.........................................350 lb 100’ Column of Water Exerts Hydrostatic Pressure of.....................................................................43.3 psi Clay (SG=2.5)...................................................................875 ppb Barite (SG=4.3) ................................................................1506 ppb Calcium Carbonate (SG=2.7) ..........................................945 ppb 1 Barrel (42 Gallons) .......................................................5.6146 cu ft 1 Cubic Foot ....................................................................7.48 gal
Conversion Formulas MULTIPLY BY TO OBTAIN sp gr (specific gravity) ..............62.4 ............pcf (pounds/cubic feet) sp gr .............................................8.34 ..........ppg (pounds/gallon) ppg (pounds/gallon)...................0.052 ........psi/ft bbl (barrels) .................................0.157 ........m3 (cubic meters) bbl ..............................................42.0 ............gal bbl ................................................5.615 ........ft3 (cubic feet) ft3 (cubic feet) ..............................0.0283 ......m3 ft3 ..................................................7.48 ..........gal gal (gallons).................................0.00379 ....m3 lb (pounds)..................................0.454 ........kg (kilograms) miles.............................................1.609 ........km (kilometers) ft (feet) .........................................0.305 ........m (meters) in. (inches)...................................2.54 ..........cm (centimeters psi (pounds/in2)...........................6.895 ........kPa (kilo-Pascals) psi.................................................0.069 ........bar psi.................................................0.07 ..........kg/cm2 kg/m.............................................0.01 ..........kP/m sp gr .......................................1000.0 ............kg/m3 ppg (pounds/gallon) ...............119.8 ............kg/m3 ppg ...............................................0.1198 ......kg/liter pcf (pounds/cubic feet) ............16.02 ..........kg/m3 ppb (pounds/barrel) ...................2.85 ..........kg/m3 psi/ft ...........................................22.61 ..........kPa/m
Density of Common Materials Specific Gravity of Common Materials (Average)
Clays, Drilled Solids
Hole Capacities HOLE DIAMETER (INCHES) 4 3/4 5 5/8 5 7/8 6 6 1/8 6 1/4 6 1/2 6 5/8 6 3/4 6 7/8 7 3/8 7 5/8 7 3/4 7 7/8 8 3/8 8 1/2 8 5/8 8 3/4 9 1/2 9 5/8 9 7/8 10 5/8 12 1/4 13 1/2 14 3/4 17 1/2 26
CAPACITY (BPF) .0219 .0307 .0335 .0350 .0364 .0379 .0410 .0426 .0442 .0459 .0528 .0564 .0583 .06.2 .0681 .0701 .0722 .0734 .0876 .0899 .0947 .1096 .1456 .1769 .2112 .2973 .6563
CAPACITY (GPF) .92 1.29 1.41 1.47 1.53 1.59 1.72 1.79 1.86 1.93 2.22 2.37 2.45 2.53 2.88 2.94 3.03 3.12 3.68 3.78 3.98 4.60 6.12 7.43 8.87 12.49 27.56
Formula: Volume (Barrels) = (Hole Diameter in Inches)2 * Length in Feet 1029.44 OR
(Hole Diameter in Inches)2 * .(Length in Feet) * 0.00097 C.3
Pounds per Hour Drilled Solids — Fast Rates
Pounds per Hour Drilled Solids — Slow Rates
Solids Content Chart
SOLIDS CONTENT - % BY VOLUME
on od C
Go s in ds d u i ater d M sol C &W Fiel inimum f s s o d e m oli lid ang ty S So te R ravi a G m i h rox Hig App sing u t n onte sC d i l So
13 14 15 16 MUD WEIGHT - LBS/GAL
Pre-well Project Checklist Well Design:
Where is the well being drilled? What type of well is it — wildcat, development, injection, etc. What problems are anticipated?
What are the hole size, casing points, and washout factors? What is the expected rate of penetration? What type bit? What is the mud program? Are there any environmental restrictions? What rig is being considered? Any anticipated hole problems?
Equipment and Vendor Capability:
What size and type of solids need removal? What equipment is already installed? What is its process rate and expected removal efficiency? Are there sufficient mud compartments? Is the equipment installed properly? What additional equipment is needed? What is expected downtime? What are the power and fuel requirements? What rig modifications are required? What is vendor experience and safety record? Is H&S Plan available? Where is the location? Where is the local stock/service base? What on-site spares are required? How many additional people are required? Do they need housing or meals? What personal protective equipment is required?
What are the preferred mud treatment and disposal options? What are preferred cuttings treatment and disposal options? Is analytical testing required? What is the mud cost? What is the equipment acquisition and installation cost? What is the expected operating cost? What is the expected disposal and site remediation cost? What are the expected savings?
Screen Cloth Comparisons SCREEN CLOTH TYPE MARKET GRADE CLOTH
TENSILE BOLTING CLOTH
EXTRA FINE CLOTH, 3-LAYERED
HIGH CONDUCTANCE CLOTH, 3-LAYERED
SCREEN DESIGNATION 10x10 20x20 30x30 40x40 50x50 60x60 80x80 100x100 120x120 150x150 200x200 250x250 325x325 20 30 40 50 60 70 80 94 105 120 145 165 200 230 24 38 50 70 84 110 140 175 210 250 45 50 60 70 80 100 125 150 180 200 230 265 310
SEPARATION POTENTIAL, IN µ D16 D50 D84 1678 839 501 370 271 227 172 136 114 102 72 59 43 1011 662 457 357 301 261 218 175 160 143 116 104 84 72 508 317 234 171 131 107 86 66 57 51 270 216 184 158 145 112 92 78 62 52 47 39 35
1727 864 516 381 279 234 177 140 117 105 74 62 44 1041 681 470 368 310 269 224 180 165 147 119 107 86 74 715 429 324 234 181 151 118 95 81 72 353 274 240 208 186 142 120 107 85 69 60 50 45
1777 889 531 392 287 241 182 144 120 108 76 63 45 1071 700 483 379 319 277 230 185 170 151 122 110 88 76 824 528 390 274 223 185 143 113 100 85 379 301 267 221 192 154 131 117 93 77 69 55 51
CONDUCTANCE IN KD/MM 49.68 15.93 8.32 4.89 2.88 2.40 1.91 1.44 1.24 1.39 0.68 0.78 0.44 0.93 24.33 11.63 7.94 5.60 5.25 3.88 2.84 2.77 2.51 2.03 1.86 1.49 1.30 20.69 11.86 6.77 4.73 3.62 3.00 2.38 1.86 1.67 1.45 9.81 7.66 5.75 5.01 4.08 3.00 2.53 2.15 1.82 1.55 1.27 0.96 0.82
Brandt/EPI Vibrating Screen Separators MODEL
Motion Screens/deck Screen Angle Deck Type
Scalping deck, also available as drying shaker
Low profile ATL
Cascade tandem over ATL
Low profile cascade shaker
Dewatering deck (patent pending)
Cascade version of LCM-2D
Dual, triple, and quad available
Dual units available
Screen Type Screen Area Vibrator G-Force
DIMENSIONS WEIGHT, LXWXH LBS
L = linear, C = circular, E = unbalanced elliptical number of screen panels in each deck, beginning with the top deck F = fixed, A = adjustable O = overslung screens, U = underslung screens, F = flat
SCREEN VIBRATOR AREA, SQ FT
H = hook strip screen, P = pre-tensioned panel Total screen area, beginning w/ top deck. If Pinnacle® screens are used, multiply area X 1.4 B = belt, G = gear box, C = canister direct drive Total acceleration, beginning with the top screen basket.
Brandt/EPI Mud Conditioners ATL-16/2
1000 gpm, three-stage mud conditioner 1680 gpm, two-stage mud conditioner 1000 gpm, three-stage mud conditioner
Brandt/EPI Liquid Recovery Shakers MODEL
SCREEN AREA, SQ FT VIBRATOR
DIMENSIONS WEIGHT, LXWXH LBS
Motion Screens/deck Screen Angle Deck Type
L = linear, C = circular, E = unbalanced elliptical number of screen panels in each deck, beginning with the top deck F = fixed, A = adjustable O = overslung screens, U = underslung screens, F = flat
Screen Type Screen Area Vibrator G-Force
COMMENTS includes liquid recovery tank and pump includes liquid recovery tank and pump
H = hook strip screen, P = pre-tensioned panel Total screen area, beginning w/ top deck. If Pinnacle® screens are used, multiply area X 1.4 B = belt, G = gear box, C = canister direct drive Total acceleration, beginning with the top screen basket.
Brandt/EPI Degassers NOMINAL FLOW, VACUUM RANGE GPM INCHES HG
BAFFLE AREA, SQ. IN
7-20 - 29 max
Rated top performing unit in comparative degasser test conducted by Amoco Production Research.
7-20 - 29 max
Similar design to DG-5, larger capacity.
VJ = vacuum, emptied by jet pump
E = electric, H = hydraulic
Brandt/EPI Hydrocyclones MODEL
Poly w/ ceramic liner
Fixed, available in 1.5”, 1.75”, and 2.125” apex Adjustable 0.125” to 0.69”
Three piece cone, available as 1, 2, or 3-cone units, upright or canted header configuration
Two piece cone, available in 4-32 cone units
Brandt/EPI Decanting Centrifuges SC-1
ROTATING ASSY CS
Fixed/ single lead
1600/654 1650/696 2000/1022
Fixed/ double lead
Fixed/ single lead
Fixed/ double lead
Fixed/ single lead Variable/ single lead
Fixed/ single lead Variable/ single lead Variable/ single lead
BOWL SIZE, IN
CS = Carbon steel, SS = Stainless steel
SPEED RANGE, RPM 1350-2000
GEARBOX RATIO 80:1
BOWL/CONVEYOR DIFFERENTIAL Fixed/ double lead
RPM/ G-FORCE 1350/466 2000/1022
CAPACITY, MUD WT/GPM 9.0/150 10.0/70.0 17.0/20 9.0/90 12.0/60 16.0/30 18.0/25 9.0/150
DIMENSIONS WEIGHT, LBS LXWXH 103x46x32 3,920
COMMENTS Barite recovery, viscosity control 6 TPH (tons per hour) solids capacity Barite recovery, viscosity control 4 TPH (tons per hour) solids capacity
Barite recovery, viscosity control 6 TPH (tons per hour) solids capacity
Unweighted muds, dewatering 6 TPH (tons per hour) solids capacity
1150/451 135x62x93 1350/621 1950/1296 1750/609 9.0/160 98x69x46 2400/1145 12.0/75 2900/1672 15.0/20 3500/2435 18.0/10 4000/3181 2000/852 9.0/150 120x61x60 2500/1331 12.0/45 3000/1917 15.0/30 3250/2100 18.0/20 2000/909 9.0/250 95x69x40 2500/1420 3000/2045 3500/2784 4000/3636 4200/4000 E = electric, H = hydraulic
Excellent all-purpose centrifuge, 8 TPH (tons per hour) solids capacity Rugged high speed decanter. 5 TPH (tons per hour) solids capacity
9.0/175 12.0/60 16.0/30 18.0/25 9.0/250
High capacity, high speed decanter. 6 TPH (tons per hour) solids capacity
8 TPH (tons per hour) solids capacity
Selection of Agitator Size and Number Select the right size agitator by first locating the tank width on the right side of the graph. A recommended impeller diameter is shown across the left side. This impeller size is correlated to the mud weight and the required horsepower. Simply follow a horizontal line from the impeller diameter to the curve showing the heaviest anticipated mud weight. Now locate the nearest vertical line to the right of this point and note the required horsepower at the top of the graph.
Example: Agitators are required for a 10-foot-wide tank, 30 feet long, to maintain weighting materials in suspension for a 12 lbs/gal mud: Find the tank width (10 ft) and the recommended corresponding impeller diameter (36 in) on the graph. Follow a horizontal line from the impeller diameter to the curve of the given mud weight (12 lbs/gal mud — use the curve on the next higher mud weight). From the intersection of the mud weight curve and the impeller diameter, locate the nearest vertical line to the right and note the horsepower at the top of the graph. This particular application will require a 7.5-hp size Brandt Agitator for each 10 feet of tank length — a total of three 7.5-hp agitators. D.7