MWD and Basic Directional Drilling
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COMPUTALOG DRILLING SERVICES
MWD I Essentials Training Curriculum
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Computalog Drilling Services Technology Services Group 16178 West Hardy Road, Houston, Texas 77060 Telephone: 281.260.5700 Facsimile: 281.260.5780
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MWD I Essentials (Bombay, India) Course #110 Course Outline: Monday, June 2 through Saturday, June 7, 2003 Day One (Monday) Introduction Registration, Introductions, and Course Description
1 hour
Directional Drilling Basics Directional Drilling Applications Conventional Rotary BHA Configurations Positive Displacement Motors
2 hours
Petroleum Geology Primer Rocks and Minerals Transport and Deposition Sedimentary Rock Classifications Origin of Hydrocarbons Hydrocarbon Migration Hydrocarbon Accumulation
3 hours
Data Acquisition Methods Recorded Data Measurement Process o Recorded Data Advantages / Disadvantages Real-time Data Measurement Process Real-time Telemetry Methods o Mud Pulse Telemetry Theory of Operations Positive Pulse Telemetry Negative Pulse Telemetry Mud Pulse Telemetry Advantages / Disadvantages o Electromagnetic Telemetry Theory of Operations Electromagnetic Telemetry Advantages / Disadvantages
1 hour
1
CROL_110_revA_0306 (Bombay)
The Borehole Environment Drilling Fluid Properties o Drilling Fluid Advantages o Drilling Fluid Disadvantages Formation Properties o Formation Porosity o Formation Permeability o Pore Fluid Saturation and Density o Lithology o Formation Thickness o Shale Content Pressure Differential o Overbalanced o Underbalanced
1 hour
Day Two (Tuesday) Surveying Essentials and Quality Control 8 hours Importance of Directional Surveying Directional Surveying Terminology Directional Sensor Hardware Sensor Axes and Orientation Sensor Calibration Directional Sensor Response versus Orientation Magnetic Field Strength, Dip Angle, Horizontal and Vertical Components Calculations of Toolface, Inclination, Hole Direction Survey Quality Parameters - Gtotal, Btotal, Goxy, Boxy, Mag Dip Azimuth to Quadrant Conversions Magnetic Declination
Day Three (Wednesday) Surveying Essentials and Quality Control (continued) 3 hours Grid Convergence GEODEC Examples Factors Affecting Inclination and Hole Direction NMDC Spacing Calculations Survey Quality Control techniques Well Plan Parameters (Horizontal & Vertical Projections) and Calculation Methods
2
CROL_110_revA_0306 (Bombay)
Sensor Theory, Application, and Interpretation Gamma Ray Logging o Applications Overview o Gamma Ray Theory o Sensor Hardware Functions o Environmental Effects on the Gamma Ray Measurement o Sensor Response versus Lithology & Fluid Type o Data Interpretation o Factors Affecting Gamma Log Quality o Applications Details
5 hours
Resistivity Logging o Applications Overview o Resistivity Theory o Sensor Hardware Functions o Environmental Effects on the Resistivity Measurement o Sensor Response versus Lithology & Fluid Type o Data Interpretation o Factors Affecting Resistivity Log Quality o Applications Details
Day Four (Thursday) Log Presentations and Formats Log Heading Bit Run Summary o Run Specific Data o Mud Data o Environmental Data o Sensor Specific Data Disclaimer and Remarks Bottomhole Assembly Diagrams Main Log o Vertical Scale Time Based Depth Based • Measured Depth • True Vertical Depth Correlation Log Detail Log o Log Tracks Linear and Logarithmic Curve Scaling and Units Track 1 – Lithology
3
CROL_110_revA_0306 (Bombay)
2 hours
Track 2 – Resistivity Track 3 – Porosity Track 4 – Resistivity or Porosity Track 5 - Depth o Annotations o Typical Presentations Standard Triple Combo Repeat Sections Calibration Data Survey Report and Plots (TVD log)
Circulation System Hydraulics Function of Borehole Fluids Pressure Balance Equation Using the Hydraulic Slide Ruler to Calculate Bit Pressure Loss
3 hours
Mud Pulse Detection & Troubleshooting
2 hour
Day Five (Friday) Operational Issues Toolface Offset Measurement Procedures Introduction to MWD Field Operations Manual Open Discussion
3 hours
Review for Exam
1 hour
Lithium Battery Safety (Course #080)
4 hours
Day Six (Saturday) Written Exam
4
4 hours
CROL_110_revA_0306 (Bombay)
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SERVICES GROUP TECHNOLOGY
Directional Drilling Basics
COMPUTALOG DRILLING SERVICES
• Directional drilling is defined as the practice of controlling the direction and deviation of a well bore to a predetermined underground target or location.
TECHNOLOGY
SERVICES GROUP
Introduction to Directional Drilling
COMPUTALOG DRILLING SERVICES
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Types of Directional Wells
TECHNOLOGY
• Slant • Build and Hold • S-Curve • Extended Reach • Horizontal
COMPUTALOG DRILLING SERVICES
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Directional Drilling Tools
• • • • • • • •
Drilling Tools Surveying/Orientation Services Steering Tools Conventional Rotary Drilling Assemblies Steerable Motors Instrumented Motors for geosteering applications Rotary Steerable Systems At-Bit Inclination Sensor
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• Multiple wells from offshore structure • Relief wells • Controlling vertical wells
TECHNOLOGY
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Applications of Directional Drilling
COMPUTALOG DRILLING SERVICES
TECHNOLOGY
SERVICES GROUP
Applications of Directional Drilling
• Sidetracking
• Inaccessible locations
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TECHNOLOGY
SERVICES GROUP
Applications of Directional Drilling
COMPUTALOG DRILLING SERVICES
TECHNOLOGY
SERVICES GROUP
Applications of Directional Drilling • Extended-Reach Drilling • Replace subsea wells and tap offshore reservoirs from fewer platforms • Develop near shore fields from onshore, and • Reduce environmental impact by developing fields from pads
COMPUTALOG DRILLING SERVICES
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• Drilling underbalanced
• • • •
TECHNOLOGY
SERVICES GROUP
Applications of Directional Drilling
Minimizes skin damage, Reduces lost circulation and stuck pipe incidents, Increases ROP while extending bit life, and Reduces or eliminates the need for costly stimulation programs.
COMPUTALOG DRILLING SERVICES
TECHNOLOGY
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Directional Drilling Limitations • • • • • • •
Doglegs Reactive Torque Drag Hydraulics Hole Cleaning Weight on Bit Wellbore Stability
COMPUTALOG DRILLING SERVICES
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TECHNOLOGY
SERVICES GROUP
Methods of Deflecting a Wellbore • Whipstock operations • Still used
• Jetting • Rarely used today, still valid and inexpensive
• Downhole motors • Most commonly used, fast and accurate
COMPUTALOG DRILLING SERVICES
TECHNOLOGY
SERVICES GROUP
Whipstock Operations
COMPUTALOG DRILLING SERVICES
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TECHNOLOGY
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Jetting
COMPUTALOG DRILLING SERVICES
TECHNOLOGY
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Directional Control with Rotary Assemblies • BHA types
• Design principles
• Building assembly • Dropping assembly • Holding assembly
• • • •
Side force Bit tilt Hydraulics Combination
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• Increasing Weight on Bit, increases Deviation Tendency …. and vice-versa
TECHNOLOGY
SERVICES GROUP
Weight On Bit
COMPUTALOG DRILLING SERVICES
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SERVICES GROUP
Stabilization Principle • Stabilizers are placed at specified points to control the drill string and to minimize downhole deviation • The increased stiffness on the BHA from the added stabilizers keep the drill string from bending or bowing and force the bit to drill straight ahead • The packed hole assembly is used to maintain angle
COMPUTALOG DRILLING SERVICES
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TECHNOLOGY
SERVICES GROUP
Reasons for Using Stabilizers • • • • •
Placement / Gauge of stabilizers control directional Stabilizers help concentrate weight on bit Stabilizers minimize bending and vibrations Stabilizers reduce drilling torque less collar contact Stabilizers help prevent differential sticking and key seating
COMPUTALOG DRILLING SERVICES
TECHNOLOGY
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Stabilizer Forces
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• Two stabilizer assemblies increase control of side force and alleviate other problems
TECHNOLOGY
SERVICES GROUP
Building Assemblies (Fulcrum)
COMPUTALOG DRILLING SERVICES
TECHNOLOGY
SERVICES GROUP
Building Assemblies (Fulcrum)
COMPUTALOG DRILLING SERVICES
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TECHNOLOGY
SERVICES GROUP
Dropping Assemblies (Pendulum) • To increase drop rate: • • • • •
increase tangency length increase stiffness increase drill collar weight decrease weight on bit increase rotary speed
• Common TL: • • • •
30 ft 45 ft 60 ft 90 ft
COMPUTALOG DRILLING SERVICES
TECHNOLOGY
SERVICES GROUP
Dropping Assemblies (Pendulum)
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• Designed to minimize side force and decrease sensitivity to axial load
TECHNOLOGY
SERVICES GROUP
Holding Assemblies (Packed)
COMPUTALOG DRILLING SERVICES
TECHNOLOGY
SERVICES GROUP
Application of Steerable Assemblies • • • • • •
Straight - Hole Directional Drilling / Sidetracking Horizontal Drilling Re - entry Wells Underbalanced Wells / Air Drilling River Crossings
COMPUTALOG DRILLING SERVICES
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SERVICES GROUP
Steerable Assemblies
• Build
TECHNOLOGY
• Drop • Hold
COMPUTALOG DRILLING SERVICES
Turbine Motor
Positive Displacement Motor
TECHNOLOGY
SERVICES GROUP
Mud Motors
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TM
PDM Motors
TECHNOLOGY
SERVICES GROUP
Commander
COMPUTALOG DRILLING SERVICES
TECHNOLOGY
SERVICES GROUP
Motor Selection • These are the three common motor configurations which provide a broad range of bit speeds and torque outputs required satisfying a multitude of drilling applications • High Speed / Low Torque - 1:2 Lobe • Medium Speed / Medium Torque – 4:5 Lobe • Low Speed / High Torque – 7:8 Lobe
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TECHNOLOGY
SERVICES GROUP
Motor Selection • High Speed / Low Torque (1:2) motor typically used when: • Drilling with diamond bits • Drilling with tri-cone bits in soft formations • Directional drilling using single shot orientations
COMPUTALOG DRILLING SERVICES
TECHNOLOGY
SERVICES GROUP
Motor Selection • Medium Speed / Medium Torque (4:5) motor typically used for: • Conventional and directional drilling • Diamond bit and coring applications • Sidetracking wells
COMPUTALOG DRILLING SERVICES
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• Low Speed / High Torque (7:8) motor typically used for: • Most directional and horizontal wells • Medium to hard formation drilling • PDC bit drilling applications
TECHNOLOGY
SERVICES GROUP
Motor Selection
TECHNOLOGY
SERVICES GROUP
COMPUTALOG DRILLING SERVICES
Components of PDM Motors • • • • •
Dump Sub Assembly Power Section Drive Assembly Adjustable Assembly Sealed Bearing Section
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TECHNOLOGY
SERVICES GROUP
Dump Sub Assembly • Hydraulically actuated valve located at the top of the drilling motor • Allows the drill string to fill when running in hole • Drain when tripping out of hole • When the pumps are engaged, the valve automatically closes and directs all drilling fluid flow through the motor
COMPUTALOG DRILLING SERVICES
TECHNOLOGY
SERVICES GROUP
Dump Sub • Allows Drill String Filling and Draining • Operation
- Pump Off - Open - Pump On - Closed
• Discharge Plugs • Connections
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SERVICES GROUP
Power Section • Converts hydraulic power from the drilling fluid into mechanical power to drive the bit
TECHNOLOGY
• Stator – steel tube containing a bonded elastomer insert with a lobed, helical pattern bore through the center • Rotor – lobed, helical steel rod
• When drilling fluid is forced through the power section, the pressure drop across the cavities will cause the rotor to turn inside the stator
COMPUTALOG DRILLING SERVICES
TECHNOLOGY
SERVICES GROUP
Power Section • • • •
Pattern of the lobes and the length of the helix dictate the output characteristics Stator always has one more lobe than the rotor Stage – one full helical rotation of the lobed stator With more stages, the power section is capable of greater differential pressure, which in turn provides more torque to the rotor
Performance Characteristics COMPUTALOG DRILLING SERVICES
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TECHNOLOGY
SERVICES GROUP
Drive Assembly • Converts Eccentric Rotor Rotation into Concentric Rotation – Universal Joint » Flex Rod
Constant Velocity Joint -COMPUTALOG DRILLING SERVICES
TECHNOLOGY
SERVICES GROUP
Adjustable Assembly • Can be set from zero to three degrees • Field adjustable in varying increments to the maximum bend angle • Provides a wide range of potential build rates in directional and horizontal wells
H = 1.962
o
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TECHNOLOGY
SERVICES GROUP
Sealed Bearing Section • Transmits axial and radial loads from the bit to the drillstring • Thrust Bearing • Radial Bearing • Oil Reservoir • Balanced Piston • High Pressure Seal • Bit Box Connection
COMPUTALOG DRILLING SERVICES
TECHNOLOGY
SERVICES GROUP
Motor Handbook • Every possible motor configuration is represented in the Motor Handbook • • • •
Dimensional Data Specifications Adjustable Housing Settings Performance Charts
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TECHNOLOGY
SERVICES GROUP
Motor Dimensional Data
COMPUTALOG DRILLING SERVICES
TECHNOLOGY
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Motor Specifications
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TECHNOLOGY
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Estimated Build Rates
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Performance Charts
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TECHNOLOGY
SERVICES GROUP
Using the Performance Charts • Differential Pressure • Difference between the system pressure when the drilling motor is on-bottom (loaded) and off-bottom (not loaded)
• Full Load • Indicates the maximum recommended operating differential pressures of the drilling motor
• RPM • Motor RPM is determined by entering at the differential pressure and projecting vertically to intersect the appropriate flow rate line
• Torque • Motor torque is determined by entering at the differential pressure and projecting vertically to intersect the torque line
COMPUTALOG DRILLING SERVICES
TECHNOLOGY
SERVICES GROUP
Operational Constraints • Temperature – 219 °F / 105 °C • Stator can be customized for temperatures up to 300 °F / 150 °C • Special materials and sizes of components used
• Excessive Weight on Bit • Excessive weight on bit stops the bit from rotating, and the power section of the motor is not capable of providing enough torque to power through (Motor Stalling) • Rotor cannot rotate inside of the stator, forming a seal • Continued circulation will erode and “chunk” the stator
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TECHNOLOGY
SERVICES GROUP
Operational Constraints • Motor Rotation • Rotating at bend angle greater than 1.83 degrees is not recommended (housing damage and fatigue) • Speed of rotation should not exceed 60 RPM (excessive cyclic load on housing)
• Drilling Fluids • Designed to operate with practically all types of drilling fluids such as fresh and salt water, oil based fluids, mud with additives for viscosity control or lost circulation, and with nitrogen gas • Hydrogen based fluids can be harmful to elastomers • High chlorine content can cause damage to internal components • Keep solids content below 5% • Keep sand content below 0.5%
COMPUTALOG DRILLING SERVICES
TECHNOLOGY
SERVICES GROUP
Operational Constraints • Differential Pressure • Difference between the system pressure when the drilling motor is on-bottom (loaded) and off-bottom (not loaded) • Excessive pressure drop across the rotor and stator will cause premature pressure wash (chunking), and impair performance • Maximum differential is flow rate dependent; higher the flow rate the lower the allowable differential pressure
• Underbalanced Drilling • Proper gas/liquid ratio must be used to avoid motor damage • Under high pressure operation conditions, nitrogen gas may permeate into the stator and expand when tripping out of the hole causing blistering or chunking of the stator
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• Pressure increases • Pressure decreases • Loss of rate of penetration
TECHNOLOGY
SERVICES GROUP
Directional Drilling Problems
COMPUTALOG DRILLING SERVICES
• Motor Stalled or stalling • Motor or Bit Plugged • Undergauge (tight) Hole
TECHNOLOGY
SERVICES GROUP
Pressure Increases
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TECHNOLOGY
SERVICES GROUP
Pressure Decreases • • • • •
Dump Sub valve stuck open Worn or damaged stator String Washout / Twist-off Lost Circulation Gas Kick
COMPUTALOG DRILLING SERVICES
TECHNOLOGY
SERVICES GROUP
Loss of Rate of Penetration • • • • •
Bit Worn or balling Worn Stator (Weak Motor) Motor Stalled Change of Formation Drill String / Stabilizer Hang Up
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• Revolution RST – Smart Stabilizer
TECHNOLOGY
SERVICES GROUP
Rotary Steerable
COMPUTALOG DRILLING SERVICES
TECHNOLOGY
SERVICES GROUP
Benefits of Rotary Steerable • No Sliding reduces risk of buckling pipe • Continuous rotation of drillstring reduces chance of differential sticking • Reduces torque & drag due to smoother well bore curvature • Longer reach wells • Longer horizontal / lateral sections • Improved formation evaluation due to pad contact of wireline tools • Improved formation evaluation with LWD tools • Deviation control in Vertical Wells
COMPUTALOG DRILLING SERVICES
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TECHNOLOGY
SERVICES GROUP
“Push the Bit” versus “Point the Bit”
COMPUTALOG DRILLING SERVICES
• Geology • Completion and Production • Drilling Constraints
TECHNOLOGY
SERVICES GROUP
Planning a Directional Well
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• • • • •
Lithology being drilled through Geological structures that will be drilled Type of target the geologist is expecting Location of water or gas top Type of Well
TECHNOLOGY
SERVICES GROUP
Geology
COMPUTALOG DRILLING SERVICES
TECHNOLOGY
SERVICES GROUP
Completion and Production • Type of completion required (“frac job”, pumps and rods, etc.) • Enhanced recovery completion requirements • Wellbore positioning requirements for future drainage/production plans • Downhole temperature and pressure
COMPUTALOG DRILLING SERVICES
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• Selection of surface location and well layout • Previous area drilling knowledge and identifies particular problematic areas
TECHNOLOGY
SERVICES GROUP
Drilling Constraints
COMPUTALOG DRILLING SERVICES
TECHNOLOGY
SERVICES GROUP
Drilling Constraints • • • •
Casing size and depths Hole size Required drilling fluid Drilling rig equipment and capability • Length of time directional services are utilized • Influences the type of survey equipment and well path COMPUTALOG DRILLING SERVICES
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TECHNOLOGY
SERVICES GROUP
Planning • Build rates • Build and hold profiles should be at least 50m • Drop rate for S-curve wells is preferably planned at 1.5 o/30m • Kickoff Point as deep as possible to reduce costs and rod/casing wear • In build sections of horizontal wells, plan a soft landing section
COMPUTALOG DRILLING SERVICES
TECHNOLOGY
SERVICES GROUP
Planning • Avoid high inclinations through severely faulted, dipping or sloughing formations • On horizontal wells clearly identify gas / water contact points • Turn rates in lateral sections of horizontal • Verify motor build rates
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TECHNOLOGY
SERVICES GROUP
Planning • Where possible start a sidetrack at least 20m out of casing • Dogleg severity could approach 14o/30m coming off a whipstock • Identify all wells within 30m of proposed well path and conduct anticollision check
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PETROLEUM GEOLOGY PRIMER
Rocks and Minerals
1
Minerals • A mineral is a naturally occurring inorganic crystalline element or compound • Minerals have definite chemical composition and characteristic physical properties such as crystal shape, melting point, color, and hardness • Most minerals found in rocks are not pure • Examples are quartz and feldspar
Rock Classifications • A rock is a hardened aggregate composed of different minerals • Rocks are divided into three classifications on the basis of their mode of origin • Igneous • Metamorphic • Sedimentary
2
Igneous Rock • Rock mass formed by the solidification of magma within the earth’s crust or on its surface • Two principal types of igneous rock • Intrusive (plutonic), those that have solidified below the surface Granite
• Extrusive (volcanic), those that have formed on the surface Lava (Basalt)
Metamorphic Rock • Rock derived from preexisting rocks by mineralogical, chemical, and structural alterations caused by heat and pressure within the earth’s crust • Limestone Æ • Shale Æ
Marble Slate
• Metamorphism results in a crystalline texture which has little or no porosity
3
Sedimentary Rock • Rock composed of materials that were transported to their present position by wind or water • Sandstone, limestone, shale sometimes referred to as clastic rocks, which are distinguished primarily by grain size • Weathering breaks down the structure • Erosion is the removal of weathered rock • Transportation mechanisms move the eroded sediments to a basin where deposition occurs • Compaction forces from the weight of overburden sediments and cementation hardens the sediments into sedimentary rock
Sedimentary Rock • Sedimentary rocks cover 75% of the land surface of the earth’s crust • Because most sedimentary rocks are capable of containing fluids (reservoir rock) they are of prime interest to the petroleum geologists • Shale is a sedimentary rock that is not typically a reservoir rock, but it is a “source rock” for the production of hydrocarbons
Sandstone
4
The Rock Cycle • The possible sequence of events, all interrelated, by which rocks may be formed, changed, destroyed, or transformed into other types of rock
Rock Texture • Clastic Texture
(Sedimentary)
• Rock texture in which individual rock, mineral, or organic fragments are cemented together by a crystalline mineral such as calcite
• Crystalline Texture
(Metamorphic & Igneous)
• Rock texture that is the result of progressive and simultaneous interlocking growth of mineral crystals
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Sedimentary Transport & Depositional Environments
Sedimentary Transport • Tectonic forces raise lowlands above sea level, ensuring a continuing supply of exposed rock for producing sediments • Gravity causes sediments to move from high places to low • Gravity also works through water, wind, or ice to transport particles from one location to another • Gravity ultimately pulls sediments to sea level
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Sedimentary Transport Mechanisms • • • •
Mass Movement Water Transport Wind Transport Glacial Transport
Mass Movement • In high elevations • Severe weathering • Instability of steep slopes
• A large block of bedrock may separate along deep fractures or bedding planes • Rockslide or avalanche
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Water Transport • Primary means of sediment transport • The distance a sedimentary particle can be carried by water depends on: • • • •
Available water energy Size Shape Density
• The higher the water energy the larger the volume and size of sediments carried • Lighter particles become part of the suspended load, whereas heavier ones settle into the bed load • Spherical particles are more difficult to carry than randomly shaped ones • The more dense a particle is, the faster it will settle out
Wind Transport • Wind moves only minor amounts of sediment compared to water transport • High winds carry clay, silt, and sand much as a river does • In arid (desert) climates wind may act as the primary weathering and transport agent • Wind-driven sediments are often reworked and redeposited by flowing water
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Glacial Transport • Glaciers move slowly but with great weight, grinding rocks into various sized particles • Glacial sediments are often reworked and redeposited by flowing water • Can move bouldersized sediments that water and wind cannot
Depositional Environments • A place where sedimentary particles arriving at a location outnumber those being carried away • Common depositional environments: • • • • •
Fluvial Lacustrine Glacial Aeolian Marine
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Fluvial Deposits • Sediments deposited by flowing water • Sediments accumulate where the energy is reduced (inside of bend) • Sandbars • Floods • Deltas
Lacustrine Deposits • A collection of sediment in a lake at the point at which a river or stream enters • When flowing water enters the lake, the encounter with still water absorbs most or all of the stream’s energy, causing its sediment load to be deposited • Eventually the lake will fill with sediments and ceases to exist, leaving behind a deposit from which hydrocarbons may be born
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Glacial Deposits • Sediments deposited by moving ice sheets are rare because they are subject to erosion and rework by other agents • Retreating glaciers leave behind accumulations of unsorted sediments called till, which is a chaotic jumble of mud, gravel, and large rocks
Aeolian Deposits • Sediments deposited by wind, typically in arid climates • Sand dunes • Loess (thick beds of silt carried by winds from the outwash plains of glaciers
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Marine Deposits • Marine deposits are far enough seaward not to be affected by wave action or fluvial deposition • Generally associated with finer grained sediments • Reef • Turbidites
Sedimentary Rock Classifications
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Clastics • Rocks composed mostly of fragments of other rocks which are distinguished by grain size
Conglomerates • A sedimentary rock composed of pebbles of various size held together by a cementing material such as clay • Similar to sandstone but are composed mostly of grains more than 2 mm in diameter • Usually found in isolated layers; not very abundant
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Sandstones • A sedimentary rock with more than half of its grains between 1/16 mm and 2 mm • Generally composed of quartz and feldspar • Commonly porous and permeable making it a likely type of rock to find a petroleum reservoir • One fourth of all sedimentary rocks are sandstones
Shales • Distinctive, fine-grained, evenly bedded sedimentary rock composed mostly of consolidated silt or clay • Formed from fine sediments that settled out of suspension in still waters, shale occurs in thick deposits over broad areas, interbedded with sandstone or limestone • Silt grains – 1/256 mm to 1/16 mm • Clay grains – flat, plate-like crystals less than 1/256 mm across • Organic shale is thought to be the source of most of the world’s petroleum • Shales also make excellent barriers to the migration of fluid and tend to trap petroleum in adjacent porous rock • One-half to three-fourths of the world’s sedimentary rock is shale
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Evaporites • A sedimentary rock formed by precipitation of dissolved solids from water evaporating in a closed basin • Indicators of former dry climates or enclosed drainage basins • Only a small fraction of all sedimentary rocks but play a significant part in the formation of petroleum reservoirs associated with salt domes
Anhydrite
Halite
Carbonates • A sedimentary rock composed primarily of calcium carbonate (limestone) or calcium magnesium carbonate (dolomite) • Make up about one-fourth of all sedimentary rocks • Most carbonates are formed as a direct result of biological activity • Limestone forms in warm, shallow water
Limestone
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Origin of Hydrocarbons
u ta lo g
Hydrocarbons • Originally oil seemed to come from solid rock deep beneath the surface (“inorganic theory”) • Scientists showed oil-rocks were once loose sediment piling up in shallow coastal waters • Advances in microscopy revealed fossilized creatures • Chemists discovered certain complex molecules in petroleum known to occur only in living cells • That source rocks were shown to originate in an environment rich with life clinched the “organic theory”
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Chemical Factors • A hydrocarbon molecule is a chain of one or more carbon atoms with hydrogen atoms chemically bound to them • Variations are due to differences in molecular weight • Despite those differences the proportions of carbon and hydrogen do not vary appreciably • Carbon comprises 82-87% and hydrogen 1215%
Chemical Composition of Average Crude Oil & Natural Gas Element
Crude Oil
Natural Gas
Carbon
82 – 87%
65 – 80%
Hydrogen
12 – 15%
1 – 25%
Sulphur
0.1 – 5.5%
0 – 0.2%
Nitrogen
0.1 – 1.5%
1 – 15%
Oxygen
0.1 – 4.5%
0%
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Chemical Factors • Methane, the simplest hydrocarbon, has the chemical formula CH4 • Four is the maximum number of hydrogen atoms that can attach to a single carbon atom
• Petroleum is only slightly soluble in salt water • Molecules with up to four carbon atoms occur as gases • Molecules having five to fifteen carbon atoms are liquids • Heavier molecules occur as solids
• Petroleum occurs in such diverse forms as • • • •
thick black asphalt or pitch, oily black heavy crude, clear yellow light crude, and petroleum gas
Biological Factors • Each level of the food chain contributes to the accumulation of organic material, particularly at the microscopic level (protozoa and algae) • Bacteria plays an important role in recycling this decaying organic material • Aerobic (oxygenated) - requires free oxygen for their life processes (i.e., forms slime or scum) • Anaerobic (reducing) - do not require free oxygen to live and are not destroyed by its absence; takes oxygen from dissolved sulfates and organic fatty acids producing sulfides and hydrocarbons
• Although aerobic decay liberates certain hydrocarbons that some small organisms accumulate within their bodies, the anaerobics are more important in oil formation
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Petroleum Formation • For an accumulation of petroleum to form, the supply of oxygen must be cut off • Examples of where anaerobic environments exist: • • • •
Deep offshore Salt marshes River deltas Tidal lagoons
• In this environment organic waste materials and dead organisms sink to the bottom and are preserved in an anaerobic environment instead of being decomposed by oxidizing bacteria • Accumulation and compaction of impermeable clay along with the organic material help seal it off from dissolved oxygen • Transformation into petroleum is accomplished by the heat and pressure of deeper burial
Physical Factors • Certain chemical reactions occur quickly at 120°-150°F, changing the organic material trapped within the rock • Long-chain molecules are broken into shorter chains • Other molecules are reformed, gaining or losing hydrogen • Some short-chain hydrocarbons are combined into longer chains and rings
• The net result is that solid hydrocarbons are converted into liquid and gas hydrocarbons • Thus the energy of the sun, converted to chemical energy by plants, redistributed among all the creatures of the food chain, and preserved by burial, is transformed into petroleum
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The Petroleum Window • The set of conditions under which petroleum will form • Temperatures between 100°F-350°F • The higher the temperature, the greater the gas proportion • Above 350°F almost all of the hydrocarbon is changed into methane and graphite (pure carbon) • Source beds (or reservoirs) deeper than about 20,000 feet usually produce only gas
Source Rocks • Source Rock • Rock in which organic material that has been converted into petroleum
• Reservoir Rock • Rock in which petroleum accumulates
• Generally, the best source rocks are shales rich in organic matter deposited in an anaerobic marine environment • Limestone, evaporites, and rocks formed from freshwater sedimentary deposition also become source beds • Time is the final ingredient in the formation and accumulation of petroleum • Little petroleum has been found in reservoir rocks with source beds less than one million years old
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Hydrocarbon Migration
Migration • The movement of hydrocarbons from the area in which it was formed to a reservoir rock where it can accumulate • Primary migration • Movement of hydrocarbons out of the source rock
• Secondary migration • Subsequent movement through porous, permeable reservoir rock by which oil and gas become concentrated in one locality
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Primary Migration • Petroleum leaves its source rock by forces of compaction and water flow • As shale gets compressed into less space, it is not the solid mineral grains that are compressed but the pore spaces • Interstitial water is squeezed out, carrying droplets of oil in suspension and other hydrocarbons in solution • Fluids squeezed out of the more readily compressible shale source rocks will collect in the adjacent sandstone, which retains more of its original porosity
Secondary Migration • Hydrocarbons are moved through permeable rock by gravity • Compressing pore spaces containing fluid • Causing water containing hydrocarbons to flow • Causing water to push less dense petroleum fluids upward
• Effective porosity and permeability of the reservoir rocks are more important than total porosity • These factors control how easily the reservoir can accumulate fluids as well as how much it can hold
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Hydrocarbon Accumulation
Traps • Like water in a puddle, hydrocarbons collect in places it cannot readily flow out of such as: • structural high points • zones of reduced permeability • Traps are a geologic combination of impermeability and structure that stops any further migration
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Traps • The basic requirements for a petroleum reservoir are • A source of hydrocarbons • Porous and permeable rock enabling migration • Something to arrest the migration and cause accumulation
• Two major groups of hydrocarbon traps • structural, the result of deformation of the rock strata • stratigraphic, a direct consequence of depositional variations
• Most reservoirs have characteristics of multiple types • Timing is critical; the formation of the trap must occur before the arrival of the petroleum
Structural Traps Anticline Structure
• Anticlines • Created by tectonic deformation of flat and parallel rock strata • A short anticline plunging in both directions along its strike is classified as a dome
• Faults Impermeable Bed Sealing Fault
• Occur when deformational forces exceed the breaking strength of rock • Most faults trap oil and gas by interrupting the lateral continuity of a permeable formation
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Stratigraphic Traps • Result of lateral discontinuity or changes in permeability and are difficult to detect • Stratigraphic traps were not studied until after most of the world's structural oil fields were discovered • They still account for only a minor part of the world's known petroleum reserves
• Stratigraphic traps are usually unrelated to surface features • Many stratigraphic traps have been discovered accidentally while drilling structural traps
Stratigraphic Traps • Shoestring Sands
Stream Channel
• A sinuous string of sandstone winding through impermeable shales • Form complex branching networks • Create isolated “compartments” • Clues such as direction of greatest permeability and general slope of the buried land surface help find the next productive location
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Stratigraphic Traps • Lens • Isolated body of permeable rock enclosed within less permeable rock • Edges taper out in all directions • Formed by turbidity currents and underwater slides • Isolated beach or stream sand deposits • Alluvial fans
• Not extended in length
Lens Traps
Stratigraphic Traps • Pinchout • Occurs where a porous and permeable sand body is isolated above, below, and at its updip edge • Oil or gas migrates updip to the low-permeability zone where the reservoir "pinches out" Pinchout Traps
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Combination Traps • Many petroleum traps have both structural and stratigraphic features • Typically found near salt domes
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DATA ACQUISITION METHODS
Data Acquisition Methods • There are two methods in which LWD data can be acquired: • Recorded • Real-time
• We will discuss the following about each: • Measurement Process • Advantages and Disadvantages
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Recorded Data Measurement Process • LWD recorded data is obtained by sampling the downhole sensors, storing each data point in downhole memory, and retrieving the data when the toolstring is tripped out of the hole • Each data point is associated with a time from the master (or sensor) downhole clock • Depth monitoring versus time is performed on the surface during drilling • Synchronization of the surface and downhole clocks at the start of the bit run is critical • During post-run processing, the time component from the depth and data files are matched to create sensor data versus depth information that is used to create logs
Recorded Data Advantages • High data resolution • data resolution is at least as good and usually much better than real-time • real-time resolution is generally no better than 8-bit (except for survey data) • recorded resolution at least 8-bit, does go up to 16-bit • Typically replaced real-time data once it is extracted from tool memory
• Independent of Transmission Problems • no missed data due to poor detection or surface sensor problems
• Fast Sample Rates • more data points per depth interval • can store data at a much faster rate than transmission • can log the hole faster than real-time and achieve the same data quality
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Recorded Data Disadvantages • No real-time feedback • recorded data is not as useful for drilling mechanics data such as pressure and vibration (historical only) • difficult to use for pore pressure prediction and casing and coring point selection • impractical and very expensive to use recorded data for directional drilling and geosteering applications
Real-time Data Measurement Process • LWD real-time data is obtained by sampling the downhole sensors, encoding the data into a binary format, and transmitting the data through some medium to the surface • The transmission is decoded at the surface, processed into a sensor data value and associated with depth to create real-time logs • The process sounds simple, but it is extremely complex and requires a combination of events to happen perfectly for a data point to be processed
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Real-time Telemetry Methods • In LWD real-time applications there are 3 types of telemetry methods: • Positive Mud Pulse • Negative Mud Pulse • Electromagnetic
• “Telemetry” basically amounts to accessing and transmitting data to and from remote locations • The LWD industry did not create telemetry, but adapted it from other disciplines
Mud Pulse Telemetry • Mud pulse telemetry utilizes an incompressible transmission path (mud column in drillpipe) to carry pressure waves created by a downhole pulser • Sensor data can be encoded in many different ways (manchester, pulse position modulation, etc.), but all of these methods require the pressure pulses to be detected at the surface in order for the data to be decoded
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Positive Mud Pulse Telemetry
• Positive mud pulse telemetry uses a hydraulic poppet valve to momentarily restrict the flow of mud through an orifice in the pulser • This generates an increase in pressure in the form of a positive pulse or pressure wave which travels back to the surface and is detected by a transducer on the standpipe and/or pumps • Computalog’s initial LWD telemetry method will be Positive Pulse
Negative Mud Pulse Telemetry
• Negative mud pulse telemetry uses a controlled valve to vent mud momentarily from the interior of the tool into the borehole annulus • This generates a decrease in pressure in the form of a negative pulse or pressure wave which travels back to the surface and is detected at the standpipe and/or pumps
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Mud Pulse Telemetry Advantages • Simple mechanical operation • Reliable if maintained properly • Original telemetry method; 20+ years of development and improvement history
Mud Pulse Telemetry Disadvantages • Transmission medium must be incompressible (no air in mud column) • Slow data transmission rates (1 to 3 bits/sec) • Advanced signal processing techniques are required to reduce the effects of distortion and noise within the telemetry band • Limited two-way downlink capability (series of pump cycles to switch between 2 fixed modes) • Negative pulse systems require ample pressure drop below the valve to generate sufficient pulse amplitude • Positive pulse systems require the use of drillpipe screens
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Electromagnetic Telemetry • EM emitting antenna injects an electric current into the formation around the hole • An electromagnetic wave is created, which propagates in the formation while being “channeled” along the drillstring • Data is transmitted by current modulation and decoded at the surface • Propagation of EM waves along the drillstring is strongly enhanced by the guiding effect of the electrically conductive drillstring
TransmitterReceiver
Earth Antenna
Bi-directional Transmission
Emitting Antenna
Drill Bit
Injected Current
Electromagnetic Telemetry • Signal attenuation is affected by the frequency of transmission, strength of signal received, and the level of parasitic electrical interference upon the carrier signal • Works on Ohm’s Law principle (V = IR) • Computalog’s LWD system will be able to utilize EM telemetry in the future
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Electromagnetic Telemetry Advantages • No restriction on drilling fluid characteristics; drilling fluid can be incompressible or compressible (allows for use in Underbalanced Drilling applications) • Reduced survey/connection time (tool is always on; no need to cycle pumps to turn tool on and off) • Unlimited two-way communication with the downhole tool • No moving parts
Electromagnetic Telemetry Disadvantages • Slow data transmission rate (1-3 bits/sec) • Suffers higher vibration in underbalanced applications • Standard EM setup suffers extreme signal attenuation at excessive depths or if high resistivity “barrier” formations are present between the emitting antenna and surface receiver • “Extended Range” EM setup can be used to relocate the point of telemetry nearer to the surface receiver; this requires hanging off a wireline in the hole
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THE BOREHOLE ENVIRONMENT
The Borehole Environment • We will consider the borehole environment to be the borehole annulus and the formation affected by invasion of the drilling fluid • Any physical barrier between the sensor detector and the uninvaded formation rock must be accounted for prior to log interpretation • Key aspects to discuss: • Drilling Fluid Properties • Formation Properties • Formation/Borehole Pressure Differential
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Radial Borehole Profile KEY POINT: • LWD sensors do not preferentially measure the virgin formation alone; their response is affected by whatever is between the sensor and the uninvaded formation
DRILLING FLUID PROPERTIES • Drilling Fluid provides many critical functions during the drilling of a well: • • • • • •
Hole cleaning (transport of cuttings) Solids suspension (gel strength, PV/YP) Bit hydraulics (aid the bit in rock failure and chip removal) Lubricity (reduce torque and drag) Control formation damage (oil-based mud, fluid loss) Hole stability (control formation pressure, prevent hole collapse, inhibit shale swelling) • Cooling the BHA
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DRILLING FLUID PROPERTIES • Drilling fluid can also create some unfortunate “side effects”: • Decreases drilling rate as mud density increases • Causes real-time data detection problems if mud viscosity is too high • Can cause irreversible formation damage • Expensive – oil-based mud requires careful containment and cutting recycling processes • Percolates into permeable formation pore spaces (in overbalanced situations) making log interpretation more difficult and complex • Renders some logging tools unusable or ineffective (oil-based mud, salt saturated mud) and can severely alter sensor response (mud additives)
FORMATION PROPERTIES • The physical makeup of the formation will affect sensor response. Some of the properties that we must consider are: • • • • • •
Formation Porosity Formation Permeability Pore Fluid Saturation and Density Lithology Formation Thickness Shale Content
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Formation Porosity • Total porosity is the ratio of the total pore space volume to the bulk formation volume • For example, a total porosity of 25% means that per cubic foot of formation, there is ¼ cubic foot of void space dispersed throughout (a sponge is a good analogy) • Maximum theoretical porosity is 48% if the grains are same size perfect spheres stacked on end (perfect sorting, cubic packing) • Porosity is the ultimate storage space for formation fluids (gas/oil/water)
Formation Porosity • Effective porosity is the ratio of the volume of all the interconnected pores to the total volume of a rock unit • Only the pores that are connected with other pores are capable of accumulating petroleum • Effective porosity depends upon how the rock particles were deposited and cemented as well as upon later diagenetic changes
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Formation Permeability • Formation Permeability is a measure of how easily fluid flows through interconnected formation pore spaces • Permeability is a function of the size of the pore openings, the viscosity of the fluid, and the pressure acting on the fluid • By definition, one darcy of permeability is equal to 1 cc/sec of flow of 1 cp viscosity fluid from a core sample with an area of 1 cm2 at a differential pressure of 1 atm • Permeability indicates the potential mobility of the fluids from the formation during production
Formation Permeability
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