Final Drilling Fuild Lab Report

DRILLING ENGINEERING (PAB 2024) Semester May, 2011

LAB REPORT DRILLING FLUID GROUP (FRI 3-5 PM)

Members:

NUR AMIRAH BINTI ZAHTA AMINI

ID: 13898

NUR FAIRUZ IZZATI BINTI MOHD ZAIN

ID: 13572

MOHAMAD SHAMSURI BIN MAHUSSIN

ID: 13550

MOHD ZAINUDIN BIN P RAMLE

ID: 13602

MUHAMMAD SYAZWAN BIN ZAINUDDIN

ID: 13749

AHMED ABDELHAFEEZ MOHAMED

ID: 15792

AHMAD AZHARI ELHADI

ID: 15790

Lab Session : Submission Date

Friday, 3 – 5 pm, 5 August, 2011 :

Friday, 12 August, 2011

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INTRODUCTION Drilling is the process of making a hole through the subsurface rocks, it continues until we hit the reservoir. In a drilling process many systems are compiled in one drilling rig to perform drilling operations. Well control system and circulating system are among those systems used in drilling operations. Well control system: Well control is the management of the dangerous effects of unexpected high pressures on the surface equipment of drilling rigs searching for oil and gas. Some type of drilling fluid is generally used to aid in well control. Failure to manage and control these pressure effects can cause serious equipment damage and injury or loss of life. Well control situations that are improperly managed cause blowouts, which is the uncontrolled and explosive expulsion of fluids from the well, usually resulting in a fire. Mud system: Effective solids control can be attributed to the overall performance of all the components of the mud systems. Conditioning the drilling fluid with the goal of dramatically lowering maintenance cost, avoiding excessive chemical treatment and maintaining mud systems volume will decrease the chance of equipment failure, unnecessary high mud costs, hole and drilling problems. In the early oil industry open earthen pits were used as settling area to separate solids and mud thereby acting as a solids control equipment. Now, with the stringent environmental regulations and high mud costs, the economics of an effective mud system come into consideration. Different solids control companies introduce zero-discharge systems, closedloop systems, "quick move" technology, screening technology, disposal options etc. Different Sections of surface mud systems: 1. Removal Section. Separation of undesirable drilled solids and even gas occurs in this section. 2. Addition Section. Commercial chemicals are being added and agitated to control and condition the mud. 3. Suction and Testing Section. This is the last part of the mud systems wherein evaluation and testing procedures are conducted before re-circulating the fluid to downhole. Drilling fluid: Drilling fluid is any of a number of liquid and gaseous fluids and mixtures of fluids and solids (as solid suspensions, mixtures and emulsions of liquids, gases and solids) used in operations to drill boreholes into the earth. Synonymous with "drilling mud" in general usage, although some prefer to reserve the term "drilling fluid" for more sophisticated and welldefined "mud". 2

Types of drilling muds: Many types of drilling fluids are used on a day-to-day basis. Some wells require that different types be used at different parts in the hole, or that some types be used in combination with others. The various types of fluid generally fall into a few broad categories: 1. Air: Compressed air is pumped either down the bore hole's annular space or down the drill string itself. 2. Air/water: The same as above, with water added to increase viscosity, flush the hole, provide more cooling, and/or to control dust. 3. Air/polymer: A specially formulated chemical, most often referred to as a type of polymer, is added to the water & air mixture to create specific conditions. A foaming agent is a good example of a polymer. 4. Water: Water by itself is sometimes used. 5. Oil-based mud (OBM): Oil-based mud can be a mud where the base fluid is a petroleum product such as diesel fuel. Oil-based muds are used for many reasons, some being increased lubricity, enhanced shale inhibition, and greater cleaning abilities with less viscosity. Oil-based muds also withstand greater heat without breaking down. The use of oil-based muds has special considerations. These include cost and environmental considerations. 6. Synthetic-based fluid (SBM): Synthetic-based fluid is a mud where the base fluid is a synthetic oil. This is most often used on offshore rigs because it has the properties of an oil-based mud, but the toxicity of the fluid fumes are much less than an oilbased fluid. This is important when men work with the fluid in an enclosed space such as an offshore drilling rig. 7. Water-based mud (WBM): A most basic water-based mud system begins with water, and then clays and other chemicals are incorporated into the water to create a homogenous blend resembling something between chocolate milk and malt (depending on viscosity). The clay (called "shale" in its rock form) is usually a combination of native clays that are suspended in the fluid while drilling, or specific types of clay that are processed and sold as additives for the WBM system. The most common of these is bentonite, frequently referred to in the oilfield as "gel". Gel likely makes reference to the fact that while the fluid is being pumped, it can be very thin and free-flowing (like chocolate milk), though when pumping is stopped, the static fluid builds a "gel" structure that resists flow. When an adequate pumping force is applied to "break the gel", flow resumes and the fluid returns to its previously free-flowing state. Many other chemicals (e.g. potassium formate) are added to a WBM system to achieve various effects, including: viscosity control, shale stability, enhance drilling rate of penetration, cooling and lubricating of equipment.

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On a drilling rig, mud is pumped from the mud pits through the drill string where it sprays out of nozzles on the drill bit, cleaning and cooling the drill bit in the process. The mud then carries the crushed or cut rock ("cuttings") up the annular space ("annulus") between the drill string and the sides of the hole being drilled, up through the surface casing, where it emerges back at the surface. Cuttings are then filtered out with either a [shale shaker], or the newer shale conveyor technology, and the mud returns to the mud pits. The mud pits let the drilled "fines" settle; the pits are also where the fluid is treated by adding chemicals and other substances. The returning mud can contain natural gases or other flammable materials which will collect in and around the shale shaker or conveyor area or in other work areas. Because of the risk of a fire or an explosion if they ignite, special monitoring sensors and explosion-proof certified equipment is commonly installed, and workers are advised to take safety precautions. The mud is then pumped back down the hole and further re-circulated. After testing, the mud is treated periodically in the mud pits to ensure properties which optimize and improve drilling efficiency, borehole stability, and other requirements listed below. Composition of drilling mud: Water-based drilling mud most commonly consists of bentonite clay (gel) with additives such as barium sulfate (barite), calcium carbonate (chalk) or hematite. Various thickeners are used to influence the viscosity of the fluid, e.g. xanthan gum, guar gum, glycol, carboxymethylcellulose, polyanionic cellulose (PAC), or starch. In turn, deflocculants are used to reduce viscosity of clay-based muds; anionic polyelectrolytes (e.g. acrylates, polyphosphates, lignosulfonates (Lig) or tannic acid derivates such as Quebracho) are frequently used. Red mud was the name for a Quebracho-based mixture, named after the color of the red tannic acid salts; it was commonly used in 1940s to 1950s, then was made obsolete when lignosulfonates became available. Other components are added to provide various specific functional characteristics as listed above. Some other common additives include lubricants, shale inhibitors, and fluid loss additives (to control loss of drilling fluids into permeable formations). A weighting agent such as barite is added to increase the overall density of the drilling fluid so that sufficient bottom hole pressure can be maintained thereby preventing an unwanted (and often dangerous) influx of formation fluids. 1. 2. 3. 4. 5. 6. 7. 8. 9.

Drilling fluid Functions: Remove cuttings from well. Suspend and release cuttings. Control formation pressures. Seal permeable formations. Maintain wellbore stability. Minimizing formation damage. Cool, lubricate, and support the bit and drilling assembly. Transmit hydraulic energy to tools and bit.

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Water based mud is created in this experiment using distilled water, Bentonite and then Parite was added to increase mud density. A number of tests have been run on the mud to measure some properties such as Density, viscosity, Gel strength and Rheology.

OBJECTIVE OF EXPERIMENT This experiment has been run to measure the properties of drilling mud, the main objectives are: 1. To measure mud density. 2. To measure mud viscosity. 3. To measure Gel strength of the mud. 4. To measure mud Rheology. 5. To know the effect of increasing mud density on the other properties.

PROCEDURES A number of tests have been run on this experiment to determine drilling fluid properties, these tests are such as: Creating drilling mud: The mud is created by adding 22.4gm of bentonite to 250 ml of water. The mixture is mixed well by adding the bentonite spoon by spoon to the water in the mixing machine to make it more homogeneous. Density test: The density of the drilling fluid must be controlled to provide adequate hydrostatic head to prevent influx of formation fluids, but not so high as to cause loss of circulation or adversely affect the drilling rate and damaging the formation. The Baroid Mud Balance is used to determine density of the drilling fluid. The instrument consists of a constant volume cup with a lever arm and rider calibrated to read directly the density of the fluid. The cup is completely filled with the mud then the lid is replaced and rotated until firmly seated and some of the mud is expelled through the hole in the cup, then the mud outside the cup is washed and wiped, after that the balance arm is placed on the base with the knife-edge resting on the fulcrum, the rider is moved until the graduated arm is level as indicated by the level vial in the beam, density is then read in the unit of (bbg).

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Viscosity test: Using the Marsh Funnel in an upright position, the orifice covered with a finger, the collected sample of the mud is poured through the screen into a clean, dry funnel until the fluid level reached the bottom of the screen, the time required for the mud to fill the receiving screen is then measured after removing the finger from the orifice, then the result is reported to the nearest second as Marsh Funnel Viscosity. Mud Rheology test: A viscometer is used to determine single or multi-point viscosities. It has fixed speeds of 3 (GEL), 100, 200, 300 and 600 RPM that are switch selectable with the RPM knob. The mud sample is placed in the cup that is located under the sleeve, then the housing is lowered to it’s normal position, the knurled knob is turned between the rear support posts to raise or lower the rotor sleeve until it is immersed in the mud sample to the scribed line, the sample is then stirred for 5 seconds at 600 RPM then the desired RPM is selected, then the dial reading and RPM is recorded after it is stabilized. Gel Strength measurements: The Mud sampled is stirred in the viscometer at 600 RPM for about 15 seconds, then the RPM knob is turned to STOP position, and waited for the desired time (10 seconds or 10 minutes), the RPM is then turned to Gel position (3 RPM), the maximum deflection of the dial before the Gel breaks is then recorded. Filtration test: The low pressure test is made using standard cell under the API condition of100 + 5 psi for 30 minutes at room temperature. First the mud cell is detached from filter press frame, the bottom of the filter cell is removed to place right size filter paper in the bottom of the cell, then the mud sample is introduced into the cup assembly, the clamp is tightened and screwed after putting filter paper and screen in top of mud sample, with the air pressure valve closed, the mud cup assembly is clamped to the frame while holding the filtrate outlet end finger tight, a graduated cylinder is then placed underneath the outlet to collect filtrate, the pressure valve is then opened and timing is started at the same moment, cc of filtrate is then recorded every 3 minutes up to 30 minutes. After finishing this test the mud cake thickness is measured and recorded down. Effect of adding weight material (Barite): The amount of barite required to increase density of mud to 10 ppg is calculated and found to be 79.4 gm. The required amount is then added to the created mud from water and bentonite and the same tests with the same procedure is the run.

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RESULT RESULTS OF MUD PROPERTIES TEST WATER BASED MUD (Density, Viscosity) Sample No. 1 2

Mud Weight 8.6 9

Marsh Funnel Viscosity (sec) 19.99 19.42

RHEOLOGY CALCULATIONS 1. Plastic viscosity (in centipose-up) Plastic viscosity = µp = 600 RPM reading – 300 RPM reading Sample 1: µp = 16.5 - 10 = 6.5 cp Sample 2 : µp = 26 – 17.5 = 8.5 cp 2. Apparent viscosity (in centipose-up) Apparent = µa = 600 RPM reading 2 Sample 1 : µa = 16.5/ 2 = 8.25 cp Sample 2 : µa = 26/2 = 13 cp 3. Yield point (in lb/100ft2) Yield point = Yp = 300 RPM reading – Plastic viscosity Sample 1 : Yp = 10 – 6.5 = 3.5 lb/100ft2 Sample 2: Yp = 17.5 – 8.5 = 9 lb/100ft2 MUD RHEOLOGY TEST WATER BASE MUD

Sample No.

1 2

Viscosity Cp ᶲ600

ᶲ300

ᶲ200

ᶲ100

ᶲ6

ᶲ3

µp

µa

Yp

16.5 26

10 17.5

8.5 15

6 10

4 7

2 5

6.5 8.5

8.25 13

3.5 9

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Gel Strength lb/100ft2 Initial 10 Final 10 sec.gel min gel 2 17 4 23

FILTRATION RATE AND MUD CAKE THICKNESS Time (min) 3 6 9 12 15 18 21 24 27 30

Volume of liquid in measuring cylinder (ml) 4.5 7.0 8.5 10.0 11.5 12.5 13.5 14.5 15.5 16.5

Mud cake reading: 1st reading = 2.79 2nd reading = 2.49 3rd reading = 2.52 Average mud cake reading = 2.79 + 2.49 + 2.52 3 = 2.62 mm

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DISCUSSION OF RESULTS In experiment 1, the mud weight is measured using the Baroid Mud Balance and the value of mud weight is 8.6 ppg. Next, Marsh funnel is used to measure the mud viscosity. The time taken for the whole amount of mud to flow through the Marsh Funnel is 19.99 seconds. Then, Mud Rheology Test is conducted to determine the plastic viscosity, yield strength and gel strength of the mud. To find the value of yield point, the value of plastic viscosity must be calculated first. Therefore, with some calculation using the value of plastic viscosity, yield point can be determined which is 3.5 lb/100ft2. For the value of gel strength, it is recorded that, the initial reading in 10 seconds is 2 lb/100 ft2 and the final reading in 10 minutes is 17 lb/100 ft2. In experiment 2, the experiment is conducted same like the pervious experiment. However, a heavier mud is used as the drilling fluid by adding weight agent which is barite. The amount of Barite that is needed to be added can be determined by using this formula: Barite = 1470 (W2 - W1) 35 - W2 As we know, density is directly proportional to the mass. Therefore, by adding the weighting agent which is Barite, the mud density will be higher. Thus, the value of mud weight obtain in experiment 2 is 9 ppg. As the mud weight is now 9 ppg, the time taken for the whole amount of mud to flow through the Marsh Funnel is 19.42 seconds. In mud rheology test, it shows that, by increasing the mud weight with Barite, the yield point is also increasing to 9 lb/100 ft2. Same goes to the value ofgel strength. For the initial reading in 10 seconds, it’s increasing to 4 lb/100ft2 and for the final reading in 10 minutes,it’s also increasing to 23 lb/100 ft2. From the results of the filtration rate, we can see that the volume of liquid eliminated from the mud increases in time of 30 minutes with the total volume of 16.5 ml.Finally, the thickness of mud cake can be obtained with an average of 2.62 mm.

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Errors There are a few errors that may lead to the inaccuracy of the experimental data. Firstly, parallax error may occur when the experiment was conducted. The errors may occur during the measurement of mud weight and gel strength. The first one was when measuring the weight of Barite and Bentonite. We used a common measuring apparatus to measure their weight. But when we tried to transfer it into a cup for making drilling fluid, some of it were not really get into the cup. These influence the calculation in the result part. During the measurement of mud weight using Baroid mud balance, the case was not really full because some of the mud fluid splashed out of the case. When we tried to put back the mud into the cup, there was still some mud stacked to the wall of the balance case. This affect the next procedure when we need to measure the viscosity as the volume required to fill in the cup of viscometer was not enough but because of time constraint, we still proceed with the experiment. Lastly, the reading of viscometer. The small area of reading really affects our insight to read the measurement. Plus, it was very difficult, with time constraint, to see the maximum deflection of the needle at the viscometer.

Modification Improvement and modification really should be done to this experiment so that we can get a better result in the future experiment. A better electronic measuring device should be used to measure weight of substances. If possible, a closed measuring device where the outside conditions do not affect the measurement should be used in practice. Also, in measuring the weight of mud fluid, a better for example electronic device should be used instead of using the manual apparatus. By this also, we can get a better and more accurate result. Using digital viscometer to measure viscosity is not impossible nowadays. Looking at the difficulties of using the manual viscometer, this really should be improved. In order to get a better and accurate result, we must do the experiment calmly so that we can focus on every aspect of the experiment. Two hours of experiment yet many things to do within the time, make us impossible to really focus on everything. Hence, more time should be spared for the experiment to be conducted.

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ANSWER TO GIVEN QUESTIONS QUESTIONS ON EXPERIMENT NO. 1 1. List any five (5) very important functions of the drilling fluid?     

Transport cutting and dispose to surface -The drilling fluid brings the drilled material to the ground surface either by mud rheology and velocity. Clean drill bits - As drilling fluid exits the bit jets, fluid velocity removes cutting from the bit teeth and bit body. This prevents bit ball up situation. Provide hydrostatic pressure to control well while drilling -Hydrostatic pressure provided from drilling fluid is the primary well control. Mud weight should be high enough to control formation pressure while drilling. Prevent excessive mud loss - While drilling, clay particle will form a thin layer over porous zones called “mud cake” or "filter cake”. Mud cake acts as barrier to prevent excessive drilling fluid loss into formation and provides wellbore stability. Prevent formation damage by using reservoir drill-in fluid -While drilling long reach zone in horizontal wells, the special drilling fluid will be utilized in order to prevent formation damage.

2. What requirements should drilling fluids meet? A drilling fluid, or mud, is any fluid that is used in a drilling operation in which that fluid is circulated or pumped from the surface down the drill string, through the bit, and back to the surface via the annulus. The mud must contains the Fluid Phase (Water or Oil), Solids (to give desired mud properties), lnactive Solids - do not react within mud to give required mud weight, Active solids - clays that react with chemicals cause further viscosity and yield point, and Additives - aid to control viscosity, yield point, gel strength, fluid loss, pH value, filtration behavior. 3. Using the mud weights (ppg) obtained for Samples #1 and 2 of your experiments, calculate, how much hydrostatic pressure that each sample will exert on a formation at a depth of 10,000 ft. Hydrostatic pressure = Fluid Density x True Vertical Depth x 0.052 Sample No, 1 = 8.6 ppg x 10,000 ft x 0.052 = 4472 psi Sample No. 2 = 9 ppg x 10,000 ft x 0.052 = 4680 psi 4. What is the difference between Over-balance and Under-balance?  Over-balance Pressure lf the mud pressure is higher than the pore pressure then it is termed as over-balance pressure.  Under-balance Pressure lf the mud pressure is lower than the pore pressure then it is termed as under-balance pressure. 11

5. Estimate the mud weight needed to balance a formation pressure equivalent to 10,000 ft. depth with 0.561 psi/ft. pressure gradient. P =0.052 *MW *TVD P = hydrostatic pressure (psi) MW = Mud weight / density {ppg) TVD = True vertical depth of mud column (ft) MW=P / (0.052*TVD) Sarnple No. 1 = 4472/(0.052 *10,000) = 8.6 ppg Sample No. 2 = 4680/(0.052 *10,000} = 9 ppg

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QUESTIONS ON EXPERIMENT NO. 2 Question 1 a)

What is plastic viscosity? A measure of the internal resistance to fluid flow of a Bingham plastic, expressed as the tangential shear stress in excess of the yield stress divided by the resulting rate of shear. Resistance to flow in excess of the yield value in a plastic material. Plastic viscosity (U) is proportional to the (shearing stress-yield value) rate of shear. The coefficient of plastic viscosity is the force in excess of the yield value, tangentially applied that will induce a unit velocity gradient. Some of the causes will increase the plastic viscosity. These are dehydration, increase in solids concentration and inadequate solids control. As defined from Schlumberger Oilfield glossary: A parameter of the Bingham plastic model. PV is the slope of the shear stress/ shear rate line above the yield point. PV represents the viscosity of a mud when extrapolated to infinite shear rate on the basis of the mathematics of the Bingham model. (Yield point, YP, is the other parameter of that model.) A low PV indicates that the mud is capable of drilling rapidly because of the low viscosity of mud exiting at the bit. High PV is caused by a viscous base fluid and by excess colloidal solids. To lower PV, a reduction in solids content can be achieved by dilution of the mud.

b)

What does it characterize? The plastic viscosity indicates the flow characteristics of the mud when it is moving rapidly, in which the viscosity is not constant. For instance, in the flow of drilling mud during drilling process; a measure of the internal resistance to fluid flow attributable to the amount, type and size of solids present in a given fluid. It is expressed as the number of dynesper square centimetre of tangential shearing force in excess of the Bingham yield value that will induce a unit rate of shear. This value, expressed in centipoises is proportional to the slope of the consistency curve determined in the region of laminar flow for materials obeying Bingham’s Law of plastic flow.

c)

What is the difference between the plastic viscosity and apparent viscosity of a drilling fluid? Plastic viscosity Plastic Viscosity (PV) is the resistance of fluid to flow attributable to the amount, type and size of solids present in a given fluid. According to the Bingham plastic model, the PV is the slope of shear stress and shear rate. In the field, we can get the PV from a viscometer which typically utilized to measure shear rates in revolutions per minute (rpm) 13

Apparent viscosity Apparent viscosity is a rheological property calculated from rheometer readings performed by a mud engineer on drilling fluid. It is normally abbreviated as AV and expressed in cp (Centipoise). Centipoise is the amount of force required to move one layer of fluid in relation to another. The ratio of stress to rate of strain, calculated from measurements of forces and velocities as though the liquid were Newtonian. If the liquid is actually non-Newtonian, the apparent viscosity depends on the type and dimensions of the apparatus used.

Question 2 Which role does Gel Strength play in the drilling process? In terms of fluid mechanic, the gel strength is the ability or a measure of fluid to form gels while in drilling terms, it means the shear stress measured at low shear rate after mud has set quiescently for a period of time. Gel strength is the ability to hold the cutting in the mud during a period of time, when the drilling process is ceased. In addition, the gel strength is the function of the inter particle forces. The gel strength measurement indicates the amount of gellation that will occur after circulation ceased and the mud remains static. The more the mud gels during shutdown periods, the more pump pressure will be required to initiate circulation again.

Question 3 What type of fluids does drilling fluid belong to? Nearly all of the Corps of Engineers drilling and sampling is accomplished using one or more of four general types of drilling fluid: compressed air, foam, clear water, and water-based mud. Air and water generally satisfy the primary functions of a drilling fluid. However, additives must often be added to these fluids to overcome specific down hole problems. Air with additives is referred to as foam. Freshwater- or saltwater-based drilling fluid with additives is commonly called drilling mud. The fifth type of drilling fluid is the oil-in-water emulsion or oil-based mud. However, this category of drilling fluids is not commonly used for geotechnical engineering investigations and therefore is not discussed herein.

a. Compressed air. Compressed air is a very effective drilling fluid for drilling in dry formations in arid climates, in competent consolidated rock, or in frozen ground. Only minor modifications to a conventional drilling rig and drill bits are required to drill with compressed air as compared to drilling with mud. An air compressor with its complement of pressure gauges, safety valves, storage tank, etc., is required. A delivery hose is needed to connect the air supply to the kelly of the drill rig. A

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deflector should be placed over the borehole to deflect the cuttings which are brought to the surface by the compressed air. b. Foam. Foam or mist may be added to compressed air to enhance its performance, especially when too much water is encountered when air drilling formations such as clays and shales. Foam will help keep the cuttings separated, reduce the effects of balling and sticking, assist in removing water from the drill hole, and allow larger cuttings to be removed from the hole with the same volume of air. Because the removal of larger cuttings from the bottom of the hole is enhanced and thus helps to assure better cleaning of the hole, faster bit penetration due to less grinding of cuttings and longer bit life result. Foam is also used as a dust suppressant and will reduce air loss, which allows drilling through lost circulation zones. c. Clear water. Water is generally a cost-effective and efficient drilling fluid which has been used for numerous drilling operations. The drilling fluid is formed naturally by mixing clear water with cuttings of soil from the formation which is being drilled. In some instances, such as the drilling of formations in which temperatures are naturally at or slightly above 0 deg C (32 deg F), ice water or a brine of ice water and salt may be used as the drilling fluid. d. Water-based muds. These fluids are the workhorses of most geotechnical drilling and sampling operations. The most common additive to form a water-based mud is bentonite, although polymers have been developed and perform well for most drilling operations. These drilling fluids plus appropriate additives fulfil all primary and secondary purposes listed in paragraph 4-1. The primary disadvantages of using drilling mud are: a large volume of drilling fluid (water) is required, and a high potential for hole erosion exists. As a rule of thumb, the volume of mud required to drill a hole is approximately three times the volume of the hole. The flush or return velocity of the drilling fluid coupled with its viscosities potentially hazardous to erodible materials in boreholes. Question 4 a) What is the yield point? Yield point is the resistance to initial flow, or represents the stress required to start fluid movement. This resistance is due to electrical charges located on or near the surfaces of the particles. In engineering view, yield point is defined as the stress at which a material begins to deform plastically. Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed. Once the yield point is passed some fraction of the deformation will be permanent and non-reversible.

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b) What does it characterize? The first point at which permanent deformation of stressed specimen begins to take place. This is a point on the stress-strain curve at which the increase in strain is no longer proportional to the increase in stress. A higher yield point implies that drilling fluid has ability to carry cuttings better than a fluid of similar density but lower yield point.

c) What is the difference between Gel Strength and Yield Point of a drilling mud? The major difference between yield point and gel strength in term of hydraulics is that gel strength will not exist once the fluid is moving and the gel has been broken, while the effects of yield point will not disappear when the fluid is moving.

Question 5 Explain what you know about one point and two points curve fluids? Give one example of each type of fluids. One point curve fluid is where the data reflects a pattern of constant or proportional rheological properties of fluids such as density, viscosity, gellation. While two point curve fluids show the properties of fluid that are not constant or fluctuating. It reflects more complex properties of the fluids. For oil-based drilling fluid – liquid fraction vs pressure graph

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QUESTIONS ON EXPERIMENT NO. 4 1. List the advantages obtained by adding weighting material to mud.  Has a higher specific gravity  There are a small number of exchangeable ions, sodium calcium and magnesium  Has lower attrition rate  Helps contribute a lower solids content by volume than a comparably weighted barite drilling fluid  Changing to oil-based mud  Changing to oil emulsion mud  Decreasing water loss mud  Increasing mud density for greater wall support  Have excellent viscosity and yield strength when mixed with salt water  Helps contribute a lower solids content by volume than a comparably weighted barite drilling fluid 2. List three (3) names of weighting material.  Barite  Hematite  Calcium carbonate  Siderite  Ilmenite 3. What are the disadvantages of adding solids to the water based mud?  Stuck pipe Stuck pipe can occur after drilling has been halted for a rig breakdown while running a directional survey or when conducting other non drilling operation. The drill pipe may stick to the wall of the hole due to the formation of filter cake or a layer of wet mud solids on the wall of the hole in the formation  Lost circulation Lost circulation occurs in several type of formations including high permeable formations, fractured formations and cavernous zones. Lost circulation materials can be added to the mud to bridge or deposit a mat where the drilling fluid being lost to the formation  Heaving or sloughing hole



This occurs when shales enter the well bore after the section has been penetrated by the bit. To solve this problem, drilling is suspend the hole is conditioned (by letting the mud in circulation for a period of time) Suffering high water loss and poor sealing properties

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4. Give reasons for adding water to your mud.  The hole may be filled with water to see if the reduced density fluid will mitigate loss. If this particularly successful, the density of drilling fluid is reduced by adding water although a large quantity may be needed to make a significant reduction.  To avoid getting very rheology especially the gel this was progressive gel.

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REFERENCES 

http://webcache.googleusercontent.com/search?q=cache:X4_IzXHv8IsJ:en.wikipedia.org/w iki/Drilling_fluid+the+disadvantages+of+adding+solids+to+the+water+based+mud&cd=4 &hl=en&ct=clnk&gl=my&source=www.google.com.my

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https://docs.google.com/viewer?a=v&q=cache:0ezmgHEReI8J:material.eng.usm.my/stafho me/termizi/EBS418E%2520Petroleum%2520Eng/5_Drilling%2520Fluid.doc+reasons+for+ adding+water+to+mud&hl=en&gl=my&pid=bl&srcid=ADGEESi3LXRoINp0ZAvdS97mE JHBmwx8OHkEKYnmfsKawmtEYo40inPMf8POte8SIImxTdiK7h8VgxpM1zfWs86zmr80 pBySLy9U7i78E1yvWLxmYLtZEawYzy5QoqN71I2v3sdCFXM8&sig=AHIEtbTm6_sDhbQfDY7lmQtNvoGuIYR1g

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