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Introduction to
Directional Drilling
Wayne Longstreet
Drilling Manager - Dragon Oil (Turkmenistan) Ltd
Slide
1
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.
Slide
2
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).
Slide
3
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.
Slide
4
Historical background
(cont’d)
• 1930’s saw the first controlled directional
well drilled in Huntington Beach,
California. 1933 used to drill under
Sunnyside Cemetery in Long Beach.
• 1934 first relief well drilled in Conroe,
Texas.
Slide
5
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.
Slide
6
Reasons for Drilling
Directional Wells
Slide
7
Relief Wells
Slide
8
Faulted Formations
Slide
9
Multiple Wells from a Single Structure
Slide
10
Reach Inaccessible Locations
Slide
11
Straight Hole Control & Sidetracking
Slide
12
Horizontal and Multi-Laterals
Slide
13
Steam Assisted Gravity Drainage
Slide
14
Up and Down Dip Laterals
Slide
15
Draining Multiple Reservoirs
Slide
16
More Efficient Drainage of a
Single Reservoir
Slide
17
Geological Considerations
• Knowledge of the
local geology is
essential to the
directional driller.
Slide
18
Where Under the
Earth Are We?
Slide
19
Surveying
• Regardless of the type of survey instrument
(single-shot, multishot, steering tool, SRO Gyro, MWD, EMMWD)
three pieces of information are known.
– Survey Measured Depth.
– Borehole Inclination.
– Borehole Azimuth (corrected for true north).
Slide
20
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.
Slide
21
Survey Calculation Methods
• Average Angle
• Radius of Curvature.
• Minimum Radius of Curvature.
Slide
22
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.
Slide
23
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.
Slide
24
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.
Slide
25
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.
Slide
26
Relative Accuracy of Methods
Slide
27
Calculation
Method
Error on TVD
(ft)
Error on
Displacement
Tangential
Balanced Tangential
Average Angle
Radius of Curvature
Minimum Radius
Mercury (STL = 15’)
-25.38
-0.38
+0.19
0.00
0.00
-0.37
+43.09
-0.21
+0.11
0.00
0.00
-0.04
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.
Slide
28
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.
Slide
29
Visual
Magnetic North
True North
Angle of
Declination
Slide
30
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)
Slide
31
Minimizing Drill String Interference
• Eliminate magnetism by using “nonmag” 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.
Slide
32
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).
Slide
33
True Vertical Depth vs Measured Depth
MD
TVD
Slide
34
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.
Slide
35
Azimuth
• Wellbore direction measured in the
horizontal plane and expressed in
degrees from the North direction starting
at 0 and continuing clockwise to 360.
Slide
36
Dog Leg Severity
• AKA BUR.
• Expressed in degrees per unit of length.
Slide
37
Basic Well Planning
Slide
38
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.
Slide
39
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.
Slide
40
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.
Slide
41
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.
Slide
42
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.
Slide
43
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.
Slide
44
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.
Slide
45
Types of Directional Wells
• Build and Hold
• “S” Wells
• Slant Wells
• Horizontal Wells
• Multi-Laterals
Slide
46
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.
Slide
47
Survey Tools
Slide
48
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.
Slide
49
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.
Slide
50
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.
Slide
51
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.
Slide
52
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.
Slide
53
EM - MWD
• Uses the same triaxial inclinometers and
triaxial magnetometers as conventional
MWD.
• Transmits data to surface using Electromagnetic telemetry.
• Dependent on depth and formation
resistivity.
• Two commercial systems available.
Slide
54
Directional Drilling
Tools
Slide
55
Spiral Drill Collars
• Spiral grooves reduce
the wall contact by 40%
with a weight reduction
of only 4%
• Reduces chances of
becoming differentially
stuck.
Slide
56
Non-Magnetic Drill Collars
• Usually flush, not spiraled.
• Made from high quality
stainless steel.
Slide
57
HWDP
• Less rigid than drill collars.
• More common in the modern
era of higher build rates and
horizontal wells.
Slide
58
Stabilizers
• Indispensable part of
rotary directional BHA’s.
• Non-rotating styles
available,
Slide
59
Downhole Adjustable Stabilizers
• Essential for extended
reach directional
drilling.
• Adjustable by changing
pump pressure or by
cycling pumps.
Slide
60
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.
Slide
61
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.
Slide
62
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.
Slide
63
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.
Slide
64
Steerable Motor
• Most common tool in
use today.
• Versatile. Rotary or
slide drilling.
• Saves many trips for
BHA changes
experienced in the past.
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65
Motor Assembly Cross Section
Slide
66
Dump Valve Assembly
Slide
67
Power Section Assembly
Slide
68
Surface Adjustable Bend
Slide
69
Bearing Assembly
Slide
70
Deflection Methods
Slide
71
Whipstocks
• Most commonly used in
re-entries.
• Controllable and
versatile.
Slide
72
Jetting
• Used in soft
formations.
• Erratic results
and severe
doglegs.
• Not in common
use today.
Slide
73
Bent Sub-Straight Motor
• Not commonly used
today, since the
advent of steerable
assemblies.
• Good for low build
rates.
• Non-rotatable.
Slide
74
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.
Slide
75
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