1. Drilling Manager - Dragon Oil (Turkmenistan) Ltd
Introduction to
Directional Drilling
Wayne Longstreet
Drilling Manager - Dragon Oil (Turkmenistan) Ltd

2. Objective of Directional Drilling
Controlled directional drilling is the science of deviating a wellbore along a planned course to a subsurface target whose location is a given lateral distance and direction from the vertical.

3. Historical Background
Originally only as a remedial operation.
Now primarily a reservoir optimization tool.
First well surveying in 1920’s in Oklahoma. Acid Bottle Inclinometer.
1929 a directional inclinometer with magnetic needle first used. Acid bottle technique proved to have error margin of @10 degrees (low).

4. Historical Background (cont’d)
As more accurate survey tools developed, it was found most boreholes were “crooked”.
Thus the emerging science of geology as given a boost when it was realized that the measured depth of producing zones was in many cases different from the vertical depth.

5. Historical background (cont’d)
1930’s saw the first controlled directional well drilled in Huntington Beach, California used to drill under Sunnyside Cemetery in Long Beach.
1934 first relief well drilled in Conroe, Texas.

6. Historical background (cont’d)
Today the technology incorporates: Horizontal, EM-MWD, SAG-D, Multi-Laterals, Extended Reach Drilling, Downhole Adjustable Gauge Stabilizers, Downhole Adjustable Motors, Bicentric Bits, 3D Wells, Underbalanced Wells, River Crossings, CTU Drilling.

7. Reasons for Drilling
Directional Wells

8. Relief Wells

9. Faulted Formations

10. Multiple Wells from a Single Structure

11. Reach Inaccessible Locations

12. Straight Hole Control & Sidetracking

13. Horizontal and Multi-Laterals

14. Steam Assisted Gravity Drainage

15. Up and Down Dip Laterals

16. Draining Multiple Reservoirs

17. More Efficient Drainage of a Single Reservoir

18. Geological Considerations
Knowledge of the local geology is essential to the directional driller.

19. Where Under the
Earth Are We?

20. Surveying
Regardless of the type of survey instrument (single-shot, multishot, steering tool, SRO Gyro, MWD, EM- MWD) three pieces of information are known.
Survey Measured Depth.
Borehole Inclination.
Borehole Azimuth (corrected for true north).

21. Directional Surveying Permits
The determination of the bottomhole location relative to the surface location or another reference system.
The location of excessive doglegs or hole curvature.
The monitoring of inclination and azimuth during drilling.
The orientation of deflection tools.

22. Survey Calculation Methods
Average Angle
Radius of Curvature.
Minimum Radius of Curvature.

23. Average Angle
Calculates the average of the angles at the top and bottom of the course section and assumes this to be the inclination and direction of the wellbore.
Oldest and least accurate method.
Easiest to calculate by hand.
Accurate when BUR is small and survey stations are close together.

24. Radius of Curvature
Each course length is defined by points at the top and bottom, and the wellbore is assumed to be curved in either or both the vertical and horizontal projections.
More complex calculations than average angle.
Accurate when stations are far apart with higher rates of curvature.

25. Minimum Radius of Curvature
Projects the actual dogleg and accounts for the severity of the dogleg on the drillstring.
Most accurate method of calculation in use today.
The use of computers and programmable calculators have made this the only real tool used today.

26. Radius of Uncertainty
All tools have a range of accuracy.
The assumption is made that errors will average out, but this still leaves us with a cone of potential error.
Critical in thin sections and extended horizontal wells.
Use of LWD, Geosteering, and geology help the directional driller.

27. Relative Accuracy of Methods

28. The Earth’s Magnetic Field
Theory #1: Rotation of the earth’s mantle in relation to the liquid core is thought to produce electrical currents.
Theory #2: The internal circulation currents (similar to phenomenon observed at the periphery of the sun) of the liquid iron in the earth’s core acts as the source according to the principle of a self-excited dynamo.

29. Magnetic Declination
The angle between magnetic north and geographic north (true north) is defined as the angle of declination.
All surveys are converted to true north.
Angles of declination to the west of true north can be written as negative numbers, to the east as positive numbers.

30. Visual
True North
Magnetic North
Angle of
Declination

31. Magnetic Interference
Caused by:
Drill String.
Fish left in hole.
Nearby casing.
Geology (Iron Pyrite, Hematite)
Magnetic “hot spot” in Drill Collar.
Fluctuations in the earth’s magnetic field. (minor)

32. Minimizing Drill String Interference
Eliminate magnetism by using “non- mag” collars (monel).
The connection area can be magnetized due to mechanical torque. (azimuth errors in 10’s of degrees) Never space within 2’ of connection.
Do not space in the center. Collars are bored from both ends leaving a ridge in center and potential magnetic hot spot.

33. Drill String Interference (cont’d)
Non-mag stabilizers are magnetic near the blades (hard facing can be very magnetic).
Amount of non-mag BHA is affected by:
Latitude.
Hole Inclination.
Distance from North/South hole azimuth.
Location (Alaska has used as much as 165 ft above magnetometer).

34. True Vertical Depth vs Measured DepthMD
TVD

35. Vertical Section and Closure
VS is the length of the horizontal displacement defined by it’s azimuth in relation to the target.
Closure is the length of the horizontal displacement passing through the survey point.

36. Azimuth
Wellbore direction measured in the horizontal plane and expressed in degrees from the North direction starting at 0 and continuing clockwise to 360.

37. Dog Leg Severity
AKA BUR.
Expressed in degrees per unit of length.

38. Basic Well Planning

39. Defining Objectives
Careful planning is essential for success.
Each well will have specific objectives defined by the reservoir or business units.
The design must be tailored to meet all of the objectives.

40. Location
DD involves drilling a hole from one point in space (surface location) to another point in space (target).
Local coordinate system must be known so the target can be accurately correlated to the target.
Most directional plans will use wellhead location as 0.

41. Target Size
During drilling the trajectory is constantly monitored in relation to the target.
Costly decisions are constantly being made to ensure that the well objectives are met.
Today’s technology allows us to drill extremely accurate wells.
Cost of the well is largely dependent upon accuracy required.

42. Cost vs Accuracy
Operators often adopt arbitrary target sizes or tolerances which do not reflect the geological realities of the reservoir.
Many needless correction runs have been made.
Hard Boundaries must be clearly defined. Legal limits, fault lines, pinch outs.
Communication and Team Work required.

43. Wellbore Profile
Given surface location, target location, target tvd, and rectangular coordinates, it is possible to determine the geometric well profile from surface to bottomhole target.
General directional well types:
Straight, Build and Hold, “S” Wells, Slant Wells, Horizontal, and Multi-Lateral.

44. Determining KOP
Kick Off Point is the depth at which the well will be deviated off the vertical.
Selection of KOP is made by considering the geometrical wellpath and geological characteristics.
Optimum inclination is determined by maximum permissible BUR and location of the target.

45. Determining Build & Drop Rates
Maximum permissible build/drop rate is determined by:
Total depth of well, and hole size.
Torque & Drag limitations. High DLS results in higher T&D except in horizontal wells.
Geology - high bur’s not always possible in soft formations.
Limitations of tools, casing, drill strings.

46. Types of Directional Wells
Build and Hold
“S” Wells
Slant Wells
Horizontal Wells
Multi-Laterals

47. Anti-Collision
As platform and pad drilling becomes more popular anti-collision planning is critical.
Radius of uncertainty.
Lead angle for rotary drilling.
Accurate well plan map essential.

48. Survey Tools

49. Steering Tools
Continuous readout when drilling without rotation. Some available now that will allow slow rotation - unreliable.
Jointed pipe operations require a “wet connect” system.
Wet connects are unreliable and time consuming.
System of choice for coil drilling.

50. Magnetic Single & Multi Shots
Camera or Electronic (digital).
Very Accurate.
Still the basic surveying tool.
Multi-shot surveys used to legally confirm open hole wells drilled with MWD. Pump down - time out.

51. Gyroscopes (Gyros)
Rate Integrating Gyro (North Seeking) most common today.
Very accurate.
Used to legally confirm wellbore location of cased holes.
Most common gyro errors are caused by initial alignment or drift.

52. Drift values may range as follows:
Gyro Drift
Drift values may range as follows:
0.5 to 1 degree/min for cheap gyros (toys).
A few degrees per hour for directional gyros.
1/100th degree per hour for inertial gyros using gimbal flotation.
1/1000 degree per hour for some inertial gyros with spherical spinning rotors, supported by electrical fields. Used in space flight.

53. Mud Pulse MWD
Use coded mud pulses to transmit tool data to surface in digital (binary) form.
Pulses are converted to electrical energy by a transducer at surface and decoded by computer.
Three types: Negative Pulse, Positive Pulse, Standing Wave Generator.

54. EM - MWD
Uses the same triaxial inclinometers and triaxial magnetometers as conventional MWD.
Transmits data to surface using Electro- magnetic telemetry.
Dependent on depth and formation resistivity.
Two commercial systems available.

55. Directional Drilling Tools

56. Spiral Drill Collars
Spiral grooves reduce the wall contact by 40% with a weight reduction of only 4%
Reduces chances of becoming differentially stuck.

57. Non-Magnetic Drill Collars
Usually flush, not spiraled.
Made from high quality stainless steel.

58. HWDP
Less rigid than drill collars.
More common in the modern era of higher build rates and horizontal wells.

59. Stabilizers
Indispensable part of rotary directional BHA’s.
Non-rotating styles available,

60. Downhole Adjustable Stabilizers
Essential for extended reach directional drilling.
Adjustable by changing pump pressure or by cycling pumps.

61. Roller Reamer
Designed to maintain hole gauge.
Either 3 point or 6 point.
Near bit roller reamers help prolong bit life, without adding torque associated with near bit stabilizers.

62. Underreamers & Hole Openers
Used to wipe out bridges and keyseats, opening directional pilot holes, opening holes for casing, drilling out skin damage.
Underreamer is hydraulically operated.

63. Keyseat Wiper
Run between the top drill collar and the drill pipe.
Greater diameter than the DC’s.
If stuck, release, jar out, rotate and back ream to eliminate keyseat.

64. Bent Sub
Run on top of a straight motor.
Not in common use after the advent of steerable assemblies
If bored for mule shoe it becomes an orienting sub.

65. Steerable Motor
Most common tool in use today.
Versatile. Rotary or slide drilling.
Saves many trips for BHA changes experienced in the past.

66. Motor Assembly Cross Section

67. Dump Valve Assembly

68. Power Section Assembly

69. Surface Adjustable Bend

70. Bearing Assembly

71. Deflection Methods

72. Whipstocks
Most commonly used in re-entries.
Controllable and versatile.

73. Jetting
Used in soft formations.
Erratic results and severe doglegs.
Not in common use today.

74. Bent Sub-Straight Motor
Not commonly used today, since the advent of steerable assemblies.
Good for low build rates.
Non-rotatable.

75. Steerable Assemblies
Very versatile and controllable.
Modern method of directional drilling.
Motor bend less than 2 degrees.
Offset pads are run for high build rates.