DRILLING ENGINEERING
CHAPTER # 8
Directional Drilling and
Deviation Control
1
Definition
Directional Drilling:
The process of directing the wellbore along some
trajectory to a predetermined target.
Deviation Control:
The process of keeping the wellbore contained within
some prescribed limits, relative to inclination angle,
horizontal excursion from the vertical or both.
X-Y Plane
X – Plane = direction plane
 Y – Plane = inclination plane

2
Angles
X-Y = Plane X – angle = direction angle
 Y-Z = Plane Y – angle = inclination angle

Purpose of Directional Drilling
Res. Under lake (economics, environmental reasons)
 Offshore drilling.
 Res. beneath population centers.
 Res. beneath natural obstruction (mountains) Or
severe topographical features.
 Sidetracking out of an existing wellbore to bypass an
obstruction (fish) or explore additional producing
horizons in adjacent sectors.
 Relief well to plug a blow out.

3
Inclination and direction planes as a wellbore proceeds in
the depth plane.
4
Plan view of a typical oil and gas structure under a lake
5
Typical offshore development platform with directional
wells
6
Developing a field under a city using directionally drilled
wells
7
Drilling of directional wells where the reservoir is
beneath a major surface obstruction
8
Sidetracking around a fish
9
Using an old well to explore for new oil by sidetracking
out of the casing and drilling occasionally
10
7.1 Planning The Directional Well
Trajectory
Trajectory
Well path that will intersect given target.

First design propose the various types of paths that
can be drilled economically.

Second includes effects of geology on the bottomhole
assemblies (BHA) and other factors that could
influence the final wellbore trajectory.
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Types of Trajectories
 Build and hold trajectory penetrates target at max.
build-up angle.
 Build-hole and drop (s-shape) penetrate angle vertically
 Build-hold drop and/or hold (modified s-shape)
penetrates target at angle less than max. inclination
angle in the hold section.
 Continuous build trajectory inclination angle is
increasing.
q1 < q3 < q2 < q4
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




X3 = horizontal departure
g1 = radius of curvature
D3 = TVD true vertical depth
D1 = kick off point TVD
q = rate of inclination angle build up
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Geometry of build-and-hold type well
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7.2 Build and Hold Trajectory






Circumference = 2pr
S=rq
q in radians max. inclination angle
1 radian = 180 o/p = 57.29578 o
1o = p/180 radians
q = degrees per unit length = q/L
= inclination angle build up rate
 q = 1o/100ft
r = S /q
 r = radius of curvature
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S=gq
1
g

q
S

deg rees
q
length
1  length 
g  

q  deg rees 
1  length   180 
g  
 

q  deg rees   p 
180 1 
180 
 or q 

g1 
p q
g 1p 
(8.1)
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 q=W-T
(8.2)
 To find angle T look at triangle OBA
BA g 1 - X 3
tan T 

AO D3 - D1
T  arctan
g1 - X3
D3 - D1
(8.3a)
(8.3b)
To find angle W consider triangle OBC
CO
SinW 
BO
(8.4)
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CO = g1
BO  (OA) 2  ( BA) 2
BO  ( D3 - D1 )2  (g 1 - X 3 )2
SinW 
g1
(g 1 - X 3 )  ( D3 - D1 )
2
(8.5)
2

g1
W  arcsin 
 (g - X )2  ( D - D )2
1
3
3
1





q=W-T
18

g1

q  arcsin
 (g - X )2  ( D - D )2
1
3
3
1


 - arctan  g 1 - X 3 
D -D 

1
 3

(8.6)
Length of the arc section DC (buildup section)
DC  r1q
p
p
180
1
r1

180 q
DC 
q
q
(8.7)
19
Length of CB (Trajectory Path)
Straight at constant inclination angle can be
determined from BCO
CO
r1
tan W 

CB CB
r1
CB 
tan W
Total measured depth DM for TVD of D3 is
q
r1
Dm  D1  
q tan W
(8.8)
20
Horizontal departure at end of build up
X 2  EC
consider DOC
X 2  r1 - r1 cosq  r1 (1 - cosq )
(8.9)
True Vertical depth at end of build up section
D2  D1 - r1 sin q
(8.12)
21
Geometry for the build section
22
Measure depth and Horizontal departure before reaching
maximum angle along any part of build up.
Consider q intermediate inclination angle q
XN=Horizontal Departure at C
DN=Vertical depth
Consider DOC
DN  D1 - r1 sin q
(8.10)
X N  r1 - r1 cosq
X N  r1 (1 -1 cosq )
(8.11)
23
New measured depth for any part of the build up
DMN  D1 
q
(8.13)
q
New measured depth at TVD of (D*< D3)(D2<D*< D3)
DMP
q
 D - D1 - r1 sin q
 D1   
q 
cosq




(8.16)
Horizontal Departure X* (X2<X*< X3)
X   r(1 - cosq )  ( D - D1 - r1 sin q ) tan q
(8.18)
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For r1 < X3
D3 - D1
r1
q  180 - arcTan (
) - arcCos(
)
X 3 - r1
D3 - D1

D3 - D1 
 sin arcTan (
)
X 3 - r1 

(8.20)
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Build-hold-and-drop and hold (modified-S)
26
Directional quadrants and compass measurements
27
Vertical calculation
28
Horizontal calculation
29
Three-dimensional view of a wellbore showing components that
comprise the X, Y and Z parts of the trajectory
30
Techniques for making a positive direction change
31
7.3 Directional Drilling Tools






Stabilizing Tools
The Stiff Hook-Up
The Pendulum Hook-Up
Angle Building Hook-Ups
The Lock-in Hook-Ups
Angle Losing Hook-Ups
32
Directional drilling applications
33
Stabilizing tool
34
The use of stabilizers in directional drilling
35
Other Application of Stabilizing Tools




Key seat Guide
Avoidance of Pressure Differential Sticking
Whip stock
Knuckle Joint
36
Whip stocks
37
Knuckle joint
38
39
Using a section mill to prepare for a kick-off
40
Jetting bit
41
Jetting a trajectory change
42
Fig 8.95: A typical positive-displacement mud motor
(PDM)
43