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
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 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.