FMN – July07

DIRECTIONAL DRILLINGDIRECTIONAL DRILLING

FMN – July07

OBJECTIVES

At the end of this session, student will be able to:

Describe the applications of directional drilling techniques

Define the terms: KOP, BUR, Tangent section of the well trajectory

Perform calculation for well trajectory operation

FMN – July07

CONTENTS

Introduction

Applications

Reference Systems

Profile Planning

FMN – July07

INTRODUCTION

It is easy to drill a vertical well from the rig. But how to drill at location far away from the rig?

WELL 1

WELL 2

WELL 3

MEAN SEA LEVEL

SEABED

FMN – July07

INTRODUCTION

Directional or deviated drilling is the science of directing a wellbore along a predetermined trajectory to intersect a designated sub-surface target

There are many reasons for drilling a deviated well: …………….

FMN – July07

APPLICATION

Salt Dome Drilling Relief Drilling

Inaccessible LocationFault DrillingMultiwell Drilling

Sidetracking

FMN – July07

REFERENCE SYSTEM The position of the target must be expressed with

respect to a 3D reference system: The vertical depth below the reference point (i.e. platform) The horizontal distance traversed from the wellhead in a

Northerly direction The distance traversed from the wellhead in an Easterly

direction

FMN – July07

REFERENCE SYSTEM (cont’d)

Depth Reference: Datum:

• Mean Sea Level (MSL) • Rotary Table Elevation

(RTE) or Rotary Kelly Bushing (RKB)

Depth of a point: • Along Hole Depth (AHD)• True Vertical Depth (TVD)

TVD

AHD

MSL

RTE /RKB

FMN – July07

REFERENCE SYSTEM (cont’d)

Geographical Reference: Lateral displacement in

terms of:• Feet or Meter from WH in

Northerly and Easterly direction

• Degrees of latitude or longitude

Coordinates• Local origin will be selected

as 0,0

FMN – July07

DEVIATED WELL PROFILE

There are three types of deviated well profile:

Build and Hold

S-shaped

Deep Kick Off

FMN – July07

WELLPATH PARAMETERS

There are 3 parameters which must be considered while planning

Kick-Off Point (KOP) Build-Up Rate (BUR)

or Drop-Off Rate (DOR)

Tangent Angle

FMN – July07

KICK-OFF POINT (KOP)

KOP is the AHD at which a change in inclination of the well is initiated and the well is orientated in a particular direction (in terms of N, S, E, W)

Generally, it is easier to kick off a well in shallow formations than in deep formations

Kick off should also be initiated in a stable formation and not likely to cause drilling problems, i.e. unconsolidated clay

FMN – July07

BUILD-UP RATE / DROP-OFF RATE

BUR and DOR are the rates at which the well deviates from the vertical - usually in degrees per 100 ft drilled (θ°/100 ft)

The rate is chosen based on the drilling experience in the location and tools available

Normally, in conventional well, the rate between 1o – 3o/100 ft are used

Since the rate is constant, these section of the well form the arc of a circle

BUR more than 3o/100 ft is often called dogleg

FMN – July07

TANGENT or DRIFT ANGLE

Tangent (drift) angle is the inclination of the long straight section of the well after the BU or DO section of the well – in degrees from the vertical

Generally, the tangent angle will be between 10o to 60o. Why? • Difficult to control the trajectory of the well at angles

below 10o

• Difficult to run wireline tools into wells at angles greater than 60o

FMN – July07

PLANNING A WELL PROFILE

FMN – July07

PLANNING A WELL PROFILE Take a common well trajectory – Build and Hold

Profile

Required information: AHD of the KOP TVD and horizontal displacement of the target BUR for the BU section TVD and horizontal displacement at which the BU stops

and tangent section commences Direction in which the well is to be drilled after the KOP,

in degrees from North (defined by position of rig and target)

FMN – July07

EXAMPLE

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

Basic Data:KOP - 2,000 ftTVD of target - 10,000 ftHorizontal Disp of Target - 3,000 ftBUR - 2 degrees/100 ft

FMN – July07

EXAMPLE (cont’d)

1. Find radius or R of the build up section:

ftBUR

R 24.286622

36000

2

36000

2. Note that angle TEY = BOE.

From this information the distances BX, XE, BE, EY can be calculated.

FMN – July07

3. Calculate the tangent angle, of the well (angle TEY):

α

EXAMPLE (cont’d)

96.08000

3000tan

x

Rx

99.208000

cossin

y

xRy

95.21yx

FMN – July07

4. Calculate AHD at the end of build section, AE = AB + BE

E

EXAMPLE (cont’d)

ftAE

ftR

BE

5.30975.10972000

5.1097360

2

ftAX

ftRBX

39.307139.10712000

39.1071sin

A

5. Calculate TVD at the end of build section, AX = AB + BX X

FMN – July07

6. Calculate displacement at the end of build, XE

E

EXAMPLE (cont’d)

ft

RROPOBXE

77.207

cos

ftAT

ftXE

ET

8.105673.74705.3097

3.7470sin

3000

A

7. Calculate AHD of target,

AT = AE + ET

X

T

FMN – July07

EXERCISE

A well will be drilled with a Type 1(Build & Hold) profile.

KOP - 2500 ftTVD of target - 8000 ftHorizontal Disp of Target - 3500 ftBUR - 2.5 degrees/100 ft

Calculate drift angle, TVD and horizontal displacement at the end of build up section, and the AHD of the target.

FMN – July07

Q & A