Directional Drilling

Directional DrillingIr. Dr. Mohd Shiraz Aris

Department of Petroleum Engineering, Universiti Teknologi PETRONAS

Thursday, April 11, 13

Learning Outcomes List and describe the applications of directional drilling

techniques Carry out relevant calculations along hole depth, TVD and

departure of the end of the build up section and the along hole depth of the bottom of the hole in a build and hold well profile.

Describe the principles used in the deflection of a wellbore from a given trajectory.


Table of Content

1. INTRODUCTION

2. APPLICATIONS

3. DEPTH REFERENCE AND GEOGRAPHICAL REFERENCE SYSTEMS

4. PLANNING THE PROFILE OF THE WELL

5. CONSIDERATIONS WHEN PLANNING THE DIRECTIONAL WELL PATH

6. DEFLECTION TOOLS


Introduction In the early days of land drilling most wells were drilled

vertically, straight down into the reservoir. Although these wells were considered to be vertical, they rarely were.

Many new techniques and special tools have been introduced to control the path of the wellbore.


ApplicationTypical applications of directionally controlled drilling (a) Multi-well Platform Drilling

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(d) Sidetracking and StraighteningIt is in fact quite difcult to control the angle of inclination of any well (vertical or deviated) and it may be necessary to correct the course of the well for many reasons. For example, it may be necessary in the event of the drillpipe becoming stuck in the hole to simply drill around the stuckpipe (or fish), or plug back the well to drill to an alternative target.

(e) Salt Dome DrillingSalt domes (called Diapirs) often form hydrocarbon traps in what were overlying reservoir rocks. In this form of trap the reservoir is located directly beneath the ank of the salt dome. To avoid potential drilling problems in the salt (e.g. severe washouts, moving salt, high pressure blocks of dolomite) a directional well can be used to drill alongside the Diapir (not vertically down through it) and then at an angle below the salt to reach the reservoir.

(f) Relief WellsIf a blow-out occurs and the rig is damaged, or destroyed, it may be possible to kill the wild well by drilling another directionally drilled well (relief well) to intercept or pass to within a few feet of the bottom of the wild well. The wild well is killed by circulating high density uid down the relief well, into and up the wild well.

Figure 1 Applications of Directional Drilling


Application(b) Fault Drilling

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Application(c) Inaccessible Locations

4






Application(d) Sidetracking and Straightening

4






Application(e) Salt Dome Drilling

4






Application(f) Relief Wells

4






Depth Reference and Geographical Referencing System

The trajectory of a deviated well must be carefully planned so that the most efficient trajectory is used to drill between the rig and the target location and ensure that the well is drilled for the least amount of money possible.

When planning, and subsequently drilling the well, the position of all points along the wellpath and therefore the trajectory of the well must be considered in three dimensions



The three dimensional system that is generally used to define the position of a particular point along the well-path is:

The vertical depth of the point below a particular reference point

The horizontal distance traversed from the wellhead in a Northerly direction

The distance traversed from the wellhead in an Easterly direction



The depth of a particular point in the wellpath is expressed in feet (or meters) vertically below a reference (datum) point and the Northerly and Easterly displacement of the point is expressed in feet (or meters) horizontally from the wellhead.

Institute of Petroleum Engineering, Heriot-Watt University 5


The trajectory of a deviated well must be carefully planned so that the most efcient trajectory is used to drill between the rig and the target location and ensure that the well is drilled for the least amount of money possible. When planning, and subsequently drilling the well, the position of all points along the wellpath and therefore the trajectory of the well must be considered in three dimensions (Figure 2). This means that the position of all points on the trajectory must be expressed with respect to a three dimensional reference system. The three dimensional system that is generally used to dene the position of a particular point along the wellpath is:

The vertical depth of the point below a particular reference point The horizontal distance traversed from the wellhead in a Northerly direction The distance traversed from the wellhead in an Easterly direction


N

E

Displacement

Cross Section

Along Hole Depth

Plan View

E

N

Vertical Depth

Vertical Depth

Figure 2 Well Planning Reference Systems

Directional Drilling

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The trajectory of a deviated well must be carefully planned so that the most efcient trajectory is used to drill between the rig and the target location and ensure that the well is drilled for the least amount of money possible. When planning, and subsequently drilling the well, the position of all points along the wellpath and therefore the trajectory of the well must be considered in three dimensions (Figure 2). This means that the position of all points on the trajectory must be expressed with respect to a three dimensional reference system. The three dimensional system that is generally used to dene the position of a particular point along the wellpath is:

The vertical depth of the point below a particular reference point The horizontal distance traversed from the wellhead in a Northerly direction The distance traversed from the wellhead in an Easterly direction


N

E

Displacement

Cross Section

Along Hole Depth

Plan View

E

N

Vertical Depth

Vertical Depth

Figure 2 Well Planning Reference Systems


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Depth referencing system

Mean Sea Level, MSL Rotary Table Elevation, RTE 20 Wellhead Housing



Geographical referencing system


Wellpath PlanningThree types of deviated well profile Build and Hold

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drop off rates are constant, these sections of the well, by denition, form the arc of a circle. Build up rates in excess of 3 degrees per 100 ft are termed doglegs when drilling conventional deviated wells with conventional drilling equipment. The build up rate is often termed the dogleg severity.

(c) Tangent (or Drift) AngleThe tangent angle (or drift angle) is the inclination (in degrees from the vertical) of the long straight section of the well after the build up section of the well. This section of the well is termed the tangent section because it forms a tangent to the arc formed by the build up section of the well. The tangent angle will generally be between 10 and 60 degrees since it is difcult to control the trajectory of the well at angles below 10 degrees and it is difcult to run wireline tools into wells at angles of greater than 60 degrees.

KOP

KOP

KOP

Build Up Section

Tangential Section

Drop off Section

Figure 3 Standard Well Trajectories


Wellpath Planning S-shaped

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KOP

KOP

KOP

Build Up Section

Tangential Section

Drop off Section

Figure 3 Standard Well Trajectories


Wellpath Planning Deep kick-off

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KOP

KOP

KOP

Build Up Section

Tangential Section

Drop off Section

Figure 3 Standard Well TrajectoriesThursday, April 11, 13


Defining Well-path points Having fixed the target and the rig position, the next stage is to

plan the geometrical profile of the well to reach the target. The most common well trajectory is the build and hold profile, (vertical, build-up and tangent).

The trajectory of the wellbore can be plotted when the following points have been defined :

KOP (selected by designer) TVD and horizontal displacement of the end of the build up section. TVD and horizontal displacement of the target (defined by position of rig

and target)



Since the driller will only be able to determine the along hole depth of the well the following information will also be required: AHD of the KOP (same as TVD of KOP) Build up rate for the build up section (selected by designer) Direction in which the well is to be drilled after the KOP in degrees from

North (defined by position of rig and target) AHD at which the build up stops and the tangent section commences and AHD of the target Note: These depths and distances can be defined by a simple geometrical analysis of the well trajectory



Build-up section radius The radius R of the build up section of the well can be calculated from the build-up rate (o/100ft) :

Tangent Angle of the well can be calculated as follows:


'HQLQJWKH3RLQWVRQWKH:HOOSDWKHaving xed the target and the rig position, the next stage is to plan the geometrical prole of the well to reach the target. The most common well trajectory is the build and hold prole, which consists of 3 sections - vertical, build-up and tangent.

The trajectory of the wellbore can be plotted when the following points have been dened :

KOP (selected by designer) TVD and horizontal displacement of the end of the build up section. TVD and horizontal displacement of the target (dened by position of rig and target)

Since the driller will only be able to determine the along hole depth of the well the following information will also be required:

AHD of the KOP (same as TVD of KOP) Build up rate for the build up section (selected by designer) Direction in which the well is to be drilled after the KOP in degrees from North (dened by position of rig and target) AHD at which the build up stops and the tangent section commences and AHD of the target

These depths and distances can be dened by a simple geometrical analysis of the well trajectory (Figure 4).

Radius of the Build Up Section:The radius R of the build up section of the well can be calculated from the build-up rate ( o/100ft) :

pi pi

o ftR

R360

1002

360002

= =( ) ( )

Tangent Angle:The tangent angle, of the well (Figure 4) can be calculated as follows:

tan x=

s y= cosx

=x + y

d RD

in RD

Note : It is possible for angle x to be negative if d < R, but these equations are still valid.

Once the tangent angle is known the other points on the wellpath can be calculated as follows:


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'HQLQJWKH3RLQWVRQWKH:HOOSDWKHaving xed the target and the rig position, the next stage is to plan the geometrical prole of the well to reach the target. The most common well trajectory is the build and hold prole, which consists of 3 sections - vertical, build-up and tangent.

The trajectory of the wellbore can be plotted when the following points have been dened :

KOP (selected by designer) TVD and horizontal displacement of the end of the build up section. TVD and horizontal displacement of the target (dened by position of rig and target)

Since the driller will only be able to determine the along hole depth of the well the following information will also be required:

AHD of the KOP (same as TVD of KOP) Build up rate for the build up section (selected by designer) Direction in which the well is to be drilled after the KOP in degrees from North (dened by position of rig and target) AHD at which the build up stops and the tangent section commences and AHD of the target

These depths and distances can be dened by a simple geometrical analysis of the well trajectory (Figure 4).

Radius of the Build Up Section:The radius R of the build up section of the well can be calculated from the build-up rate ( o/100ft) :

pi pi

o ftR

R360

1002

360002

= =( ) ( )

Tangent Angle:The tangent angle, of the well (Figure 4) can be calculated as follows:

tan x=

s y= cosx

=x + y

d RD

in RD

Note : It is possible for angle x to be negative if d < R, but these equations are still valid.



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AHD at the end of build section:The measured depth at end of build section, AE:

AE = AB + BE (curved length)

BE can be calculated from BER2 360pi

=

TVD at the end of the build Section:The TVD at end of build section, AX is

AX = AB + PE

where PE = R sin AX = AB + R sin

Displacement at the end of build Section:The horizontal deviation at end of build, XE is

XE = OB - OP

where OB = R OP = R cos XE = R - R cos

AHD of the target:The total measured depth, AT is AT = AE + ET Example:The planning procedure for the build and hold trajectory is best illustrated by considering the following example:

Basic Data:

KOP (BRT) - 2000 ft TVD of target (BRT) - 10000 ft horizontal Displacement of Target - 3000 ft build-up rate - 2 degrees/100 ft



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=


AX = AB + PE



XE = OB - OP



Basic Data:




10




=


AX = AB + PE



XE = OB - OP



Basic Data:


10




=


AX = AB + PE



XE = OB - OP



Basic Data:




Exercise: The planning procedure for the build and hole trajectory is best illustrated by considering the following example:

Draw-up the trajectory for the proposed planning procedure

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=


AX = AB + PE



XE = OB - OP



Basic Data:




xy

EX

C Y T

B

A

O P R

R

1000' 2000' 3000' Displacement

2000'

4000'

6000'

8000'

10000'd

D

Figure 4 Design of the Well Trajectory

4.2.1 Scaled DiagramsUsing a scaled diagram, this information can simply be plotted on a piece of graph paper using a compass and a ruler (Figure 4). Point A represents the rig location on surface. Point B is the KOP at 2000'. Point T is the target. Point O denes the centre of the arc which forms the Buildup section.

The radius OB can be calculated from build-up rate:

i e OB

o

. .

'

. '

2360

1002

9000 2866 24= = =pi pi(OB)

An arc of this radius can be drawn to dene the build-up prole. A tangent from T can then be drawn to meet this arc at point E. The drift angle TEY can then be measured with a protractor. Note that TEY = BOE. From this information the distances BX, XE, BE, EY can be calculated.


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Tsani SabilaSticky NoteWhy horizontal departure is not at 3000ft?



where OB = R OP = R cos = 2658.47' XE = 2866.24 - 2658.47 = 207.77'

AT (total measured depth) AT = AE + ET ET can be calculated from;

ET = 8000 - 1071.39

Cos 21.95= 7470.12'

o

AT = 3097.50 + 7470.12 = 10567.62'

Exercise 1 Designing a Deviated Well

It has been decided to sidetrack a well from 1500 ft. The sidetrack will be a build and hold profile with the following specifications:

Target Depth : 10000 ft.Horizontal departure : 3000 ft.Build up Rate : 1.5o per 100 ft.

Calculate the following :

a. the drift angle of the well. b. the TVD and horizontal deviation at the end of the build up section. c. the total measured depth to the target.

5. CONSIDERATIONS WHEN PLANNING THE DIRECTIONAL WELL PATH

When planning a directional well a number of technical constraints and issues will have to be considered. These will include the:

Target location Target size and shape Surface location (rig location) Subsurface obstacles (adjacent wells, faults etc.)


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