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# 04 Directional

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• 1. Trajectory Design and Directional Drilling 1 Directional Drilling • What is Directional Drilling? “Intentional, controlled deflection of a wellbore to intersect pre-determined targets.” • Topics: – Terminology – Drivers for directional drilling – Directional tools and techniques – Measuring trajectories – Calculations – Potential problems 2
• 2. Trajectory Components True Vertical Depth Kickoff Point (KOP) Build Section Ta int Me ng Po en off as k t ur c Ki ed nd 2 De pth 2nd Build Section Lateral Horizontal Departure 3 Trajectory Measurements 0° / 360° 45° = N 45°E 295° = N65°W 270° 90° Inclination: the measure in degrees of the angle of the wellbore from vertical 155° = S25°E 200° = S20°W 180° Azimuth: the measure of the direction of the wellbore in: (1) degrees from North 45° between 0° and 360°, or (2) degrees from North or South to the East or West 4
• 3. 5 Drivers for Directional Drilling • Access to remote reservoirs from a central platform, template, or pad. – Avoid or defer capital expenditures – fewer platforms, fewer subsea installations – Monetize otherwise uneconomic reserves – offshore reserves from onshore facilities • Access to otherwise inaccessible reserves. – Environmental restrictions – Other exclusions, e.g. lakes, cities, shipping lanes 6
• 4. Directional Drilling Applications 7 Industry Directional Capabilities 8
• 5. Trajectory Options Option Advantages Disadvantages Build and hold: Constant BR to Simple; Long reaches achievable Potentially high contact force in tangent angle, hold constant Low tangent angle build (torque, casing wear) tangent angle Undersection: Build and hold Lower contact force in build section High tangent angle; Reduced with deep KOP reach Double build: Build-hold-build- Very long reaches possible with Requires deep steering; High angle hold trajectory, can use two lower contact forces in upper build in second tangent different BRs in curves. S-shaped: Includes angle drop Allows lower angle reservoir entry, Higher tangent angle for given section possibly easier intervention reach; Potentially high contact force in build (torque, casing wear) Multiple build: BR increases Much longer reach than catenary; High tangent angle with depth in several discrete Lower torque/drag steps to tangent angle, hold constant tangent angle Catenary: Continuously Lowest contact force (torque, Theoretical benefits not cost- increasing build rate (BR) with casing wear) of any trajectory effective in implementation; Limited depth, no tangent reach 3-D: Any of the above with Flexibility to handle anti-collision More curvature means more torque significant azimuth changes and multiple target requirements and drag, limited reach Multi-Lateral: branched well Increased exposure to reservoir, Limited intervention and stimulation bores from mother bore through reduced drawdown, fewer surface scenarios various junction styles facilities 9 Trajectory Options 10
• 6. Trajectory Design Criteria • Targets • Drillability • Cost • Intervention 11 Trajectory Design Criteria • Targets – Specifications • Horizontal departure • Size • Shape • Orientation – Stacked targets – Natural Drift Predictability 12
• 7. Horizontal Departure 13 Stacked Targets Final tangent angle may vary widely depending upon Horizontal Departure required to reach targets. 14
• 8. Walk Tendencies Angle Building Angle Dropping • Normal Force into the high • Normal Force into the low side of the hole = ↑ Inclination side of the hole = ↓ Inclination • With RH rotation of bit, walk • With RH rotation of bit, walk tendency is to the left. tendency is to the right. 15 Natural Drift • As directional tendencies become known for local combinations of: Formations Bits BHAs • Rig locations can be optimized to minimize expensive directional control techniques in favor of natural drift. 16
• 9. Trajectory Design Criteria • Drillability – Normal force • Curvature + Tension = Normal Force • Torque / drag: ↑ normal force = ↑ torque / drag • Casing / drill string wear: ↑ normal force = ↑ wear rates – Wellbore stability • Orientation of wellbore in the in-situ tectonic stress field will effect stresses, and therefore, stability of wellbore wall. – Hole Cleaning • Cuttings transport efficiency affected by hole inclination – Anti-collision • Constraints imposed by nearby wellbores 17 Trajectory Design Criteria • Cost – Tool selection • Availability • Familiarity / Support • Track record • Logistics – Cost-effectiveness • Cost (including Lost in Hole charges) • Time • Efficiency • Impact on other drilling systems – Failure likelihood • Failure modes – trip or fish • Recovery plans – back up plan 18
• 10. Trajectory Design Criteria • Intervention – Wireline – Coiled Tubing • Critical Angle (α) – Ability of tools to slide under their own weight without being pushed from above – α = Tan-1(1/µ) – Function of Coefficient of Friction (µ) – Ex. Where µ=0.2, α= 78.7° 19 Achieving Directional Control • Two Primary Approaches: – Push the bit: side force > side cutting – Point the bit: bit tilt • Push the bit – Traditional rotary BHAs – Bent sub motor assemblies – Rotary steerable – BHI Autotrak / Schlumberger Powerdrive • Point the Bit – Bent housing motor BHAs – Rotary steerable – Halliburton GeoPilot 20
• 11. Bit Side Force • All BHAs cause a side force at the bit • This side force may make the bit – build angle – hold angle – drop angle – turn right – turn left • The key is to control the direction and magnitude of the force. 21 Rotary BHA Configurations 90 ft 30 ft Strong angle building tendency 60 ft 30 ft Moderate angle building tendency 45 ft 30 ft Slight angle building tendency Strong holding tendency (little incl. and azim. change) 30 ft 30 ft shorter stab. spacing gives better holding capability 10-20 ft UG Moderate holding tendency - highly UG 2nd stab. may 30 ft 30 ft provide some building tendency 10-20 ft Slight holding tendency - formation tendencies to build 30 ft 30 ft 30 ft or drop angle often overpower this assembly 90 ft 30 ft Strongest angle dropping tendency (Optional stabs. make behavior more predictable 60 ft 30 ft and increase dropping tendencies) 45 ft 30 ft Weakest angle dropping tendency UG 30 ft UG near-bit stab. may moderate dropping tendency 60-90 ft Stabilizer Optional Stabilizer UG - Undergauge 22
• 12. Directional Motor BHA Configurations mot Simple motor with bent sub - prior to 1980 or BS higher side load and less bit tilt - sliding mode only Bent housing motor - early ‘80’s BH motor higher bit tilt and less side load - sliding mode only Double tilted u-joint motor - mid ‘80’s DTU motor very high bit tilt - limited string rotation BS Bent housing motor with bent sub above - lower BH motor deflections allowed string rotation and “steerability” Adjustable bent housing deflection angle AKO motor (some downhole adjustable) ADJ Downhole adjustable stabilizer allows 2-D steerability (inclination only) in rotary mode (e.g. TRACS) RST Rotary steerable tools allow downhole 3-D (inclination and azimuth) steerability in rotary mode (e.g. Autotrack) Stabilizer Optional Stabilizer ADJ - Adjustable 23 Rotary Steerable Systems • Push-the-bit – BakerHughes INTEQ Autotrak – Schlumberger Powerdrive • Oversize hole can reduce build rate High Side Orientation Ma gn Bit Side Force it ud e 24
• 13. Rotary Steerable Systems • Point-the-bit – Halliburton SperrySun Geopilot • Pair of eccentric rings • Controls orientation and magnitude of deflection Zero Maximum Intermediate deflection deflection deflection 25 Trajectory Measurement - Surveying • Measurement Types: • Inclination Only • Inclination and Azimuth • Single Shot • Multi-Shot • Tool Types: • Gravity • Magnetic • Gyroscopic • Deployment Mechanisms: • Wireline • MWD – telemetry or memory • Pipe - conveyed • Dropped • Measurement Errors • Position Uncertainty • Collision Avoidance 26
• 14. Magnetic Instrument 1. Pendulum 2. Circular Glass 3. Compass 4. Pressure equalization 5. Cover glass Inclination = 5° Direction = N 45°E or Azimuth = 45° 27 Magnetic Instrument Film Raw Reading: Inclin. = 5.5° Dir. = N35°W Must be corrected for Declination 28
• 15. Outer Gimbal Axis Typical Gyroscope Spin Axis Inner Gimbal Axis Inner Gimbal (Spin Motor) Outer Gimbal • Inertial effects keep it pointing in the same direction. • Not affected by the earth’s magnetic field, or by steel in the wellbore • Single shot or multi-shot tools available 29 Sources of Survey Errors • Instrument measurement limitations • Depth Error • North Reference Error • Magnetic Interference • Gyro Drift Errors • Instrument Alignment Errors 30
• 16. Magnetic Declination • Declination is the angle a freely turning magnetic needle makes with the imaginary line pointing to True North. True Magnetic North North Declination Angle 31 Magnetic Declination Correction West Declination East Declination (Subtract from Azimuth) (Add to Azimuth) BUT, when using oilfield direction nomenclature, declination must be added or subtracted from the magnetic compass reading, depending upon whether it is East or West declination and in what quadrant the raw heading lies. + - - + - + + - 32
• 17. Magnetic Magnetic Declination Correction North o True North 5 Example o o 115 Declination = 5 West o 110 MAGNETIC READING o o = S65 E = 115 Magnetic 65 o Corrected Azimuth = o o o 115 - 5 = 110 True 33 Magnetic Declination Correction West Declination East Declination (Subtract from Azimuth) (Add to Azimuth) 35° = N 35°E 35° = N 35°E + - - + 290° = N70°W 290° = N70°W 200° = S20°W - + 165° = S15°E + 200° = S20°W - 165° = S15°E 3° West Declination Corrects CCW: 3° East Declination Corrects CW: Direction Corrected Azimuth Corrected Direction Corrected Azimuth Corrected N 35°E N 32°E 35° 32° N 35°E N 38°E 35° 38° N70°W N73°W 290° 287° N70°W N67°W 290° 293° S15°E S18°E 165° 162° S15°E S12°E 165° 168° S20°W S17°W 200° 197° S20°W S23°W 200° 203° 34
• 18. Isogonic chart for the U.S. I Isogonic: lines of equal magnetic declination 35 Isogonic Chart for the World (2000) I Measures may change a few minutes per year. 36
• 19. Magnetic Interference. s tic r la ne e ol Li gn lC d a s ine el M e e St dL Fi h’s C iel om rt e F Ea pa nc ss fere er Int Non-magnetic Collar b t Su Bi 37 Earth’s Magnetic Field Intensity • Field intensity varies geographically. • Length of the nonmagnetic drill collars required in a BHA will vary (1) from area to area and (2) as wellbore inclination & azimuth vary. 38
• 20. Thailand is in Zone I Directional Plan: Azim: N40°W Inclination Incl: 55° Required Length of Non-Mag DC: 43 ft Direction Angle from magnetic N or S 39 UK is in Zone II Directional Plan: Azim: N40°W Incl: 55° Inclination Required Length of Non-Mag DC: 60 ft Direction Angle from magnetic N or S 40
• 21. North Slope is in Zone III Directional Plan: Azim: N40°W Inclination Incl: 55° Required Length of Non-Mag DC: 60 ft Direction Angle from magnetic N or S 41 Wellbore Position Uncertainty • Uncertainty in surveys results in uncertainty in wellbore position. • Common to have higher magnitude of uncertainty in azimuth orientation (L-R) than inclination orientation. • Calculated uncertainty shows boundaries of EoUs. • EoU Separation guidelines should be agreed beforehand 42
• 22. Ellipse of Uncertainty Separation • EoU’s should never overlap • EoU Separation guidelines should be agreed beforehand 43 “Christmas Tree” of Survey Errors • Magnetic surveys like EMS and MWD typically have larger errors, and therefore larger EoUs. • Gyro surveys at casing points reduce the errors and provide smaller EoUs. 44
• 23. Position Errors by Survey Tool Type After SPE 56702 / 67616 - 1999 45 Survey Calculations Calculate position of the wellbore based upon survey data Position: TVD N-S / E-W departure (Rectangular Coordinates) Closure: Drift (HD) and Direction (Azimuth) (Polar Coordinates) Survey Data at each survey station: Measured Depth (MD) Inclination Azimuth Calculation Methods: Minimum Curvature Radius of Curvature Many others… Dogleg Severity (DLS) – Total rate of curvature (°/100 ft or °/30m) 46
• 24. Arc Length to Angle Change Relationship Smaller Radius r Length of arc of circle (S) α1 S1 r Radius of Curvature (R) Angle Change (α) ∆S = R∆α R S2 α2 R Larger Radius NOTE: All angles in radians 47 Survey Calculation Methods • Minimum Curvature • Radius of Curvature • Tangential • Balanced Tangential (Acceleration Method) • Trapezoidal (Vector Averaging) • Average Angle • Mercury (Combined Method) • Simpson’s Rule Method 48
• 25. Minimum Curvature Method • This method assumes that the wellbore follows the smoothest possible circular arc from one survey station to the next. • Knowns: Location of first survey point, ∆MD between surveys, and inclination and azimuth at both survey points. Ref: API Bulletin D20 (1985) 49 Minimum Curvature Method PS + SR RF = Arc PQR RF = Ratio Factor DL = Dogleg Angle  DL   DL  r tan   + r tan   O =  2   2  r r (DL ) DL P 2 2 DL r RF = tan Q DL 2 S DL R cos (DL) = cos (I2 − I1) − sin I1sin I2 (1 − cos(A 2 - A1)) NOTE: All angles in radians 50
• 26. Minimum Curvature Method - Equations ∆MD ∆North = [sin(I1 ) • cos(A1 ) + sin(I2 ) • cos(A2 )] • RF 2 ∆MD ∆East = [sin(I1 ) • sin(A1 ) + sin(I2 ) • sin(A2 )] • RF 2 ∆MD ∆Vert = [cos(I1 ) + cos(I2 )] • RF 2 2 DL Where: RF = tan DL 2 cos (DL) = cos (I2 − I1) − sin I1sin I2 (1 − cos(A 2 - A1)) NOTE: All angles in radians Ref: API Bulletin D20 (1985) 51 Radius of Curvature Method • This method assumes the wellbore follows a smooth, spherical arc between survey points and passes through the measured angles at both ends. (tangent to inclination and azimuth at both survey points). • Knowns: Location of first survey point, ∆MD between surveys, and inclination and azimuth at both survey points. 52
• 27. Radius of Curvature Method - Equations ∆MD • [cos(I1 ) − cos(I2 )] • [sin(A2 ) − sin(A1 )] ∆North = (I2 − I1 ) • (A2 − A1 ) ∆MD • [cos(I1 ) − cos(I2 )] • [cos(A ) − cos(A2 )] ∆East = 1 (I2 − I1 ) • (A2 − A1 ) ∆MD • [sin(I2 ) − sin(I1 )] ∆Vert = (I2 − I1 ) Ref: API Bulletin D20 (1985) NOTE: All angles in radians 53 Directional Problems • Poor response of directional tools • Industry going for more “science” and less “art” • Directional driller dependent on computer control • Tool failure / system failure • MTBF of rotary steerables and other tools • Unable to steer in sliding mode • Tortuosity • Unplanned curvature in wellbore • Increased torque, drag, casing wear 54
• 28. Sliding with Bent Housing PDMs Pipe movement Dyn Drag = 50,000 lbs 25% Static = 67,000 lbs Drag Force WOB = 10,000 lbs Static Total = 77,000 lbs Friction Dynamic Friction Pipe moves ===> WOB = 27,000 lbs, not…...10,000 lbs. Time Drag force reduced once pipe moves 55 Sliding with Bent Housing PDMs 5000 Series M121 PDC bit 4000 Typical max torque for Torque, ft-lb 6-1/2” slow-speed motor 3000 Series M332 2000 Series 517 Rollercone 1000 0 0 10 20 30 40 50 Weight-on-Bit, 1000 lb 56
• 29. Tortuosity – Unsurveyed Curvature Survey Station (n) • Survey intervals may not allow correct representation of curvature. • Calculation method assumes smoother curve than actually exists locally. Apparent Dogleg • Result is higher normal force, higher torque / drag, higher casing wear. • Lower drillability, higher cost Actual Dogleg Survey Station (n+1) 57
• 30. Notes: __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________
• 31. Notes: __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________
• 32. Notes: __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________