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JAMES A. JAMES A. CRAIGCRAIG
Table of ContentsTable of ContentsDefinitionsApplications of Directional DrillingDeflection ToolsMud MotorsTypes of Well Profile
Definitions Definitions Directional drilling is the process of directing
the wellbore along some trajectory to a predetermined target.
Deviation control is the process of keeping the wellbore contained within some prescribed limits relative to inclination, horizontal excursion from the vertical, or both.
Applications Applications History
Interests in controlled directional drilling began about 1929 after new and later accurate means of measuring hole angle was introduced during the development of Seminole, Oklahoma field.
In the early 1930’s the first controlled directional well was drilled in Huntington Beach, California.
Controlled directional drilling was initially used in California for unethical purposes, that is, to intentionally cross property lines.
In 1933, during the development of the Signal Hill field in Long Beach, California, several wells were drilled under the Sunnyside Cemetery from locations across the streets surrounding the cemetery.
In 1934, it was used to kill a wild well, Madeley No.1, near Conroe, Texas.
Typical offshore development platform with directional wells
Developing a field under a city using directionally drilled wells
Drilling of directional wells where the reservoir is beneath a major surface obstruction
Sidetracking around a fish
Using an old well to explore for new oil by sidetracking out of the casing and drilling directionally
A relief well drilled to intersect the uncontrolled well near the bottom
Salt dome drilling (direct the well away from the salt dome to avoid casing collapse problems)
Fault drilling through a steeply dipping, inclined fault plane.
Other applications include:To reach multiple targetsHorizontal drillingTo reach thin reservoirs (using horizontal and
multilateral drilling)To avoid gas or water coning problems
Deflection ToolsDeflection ToolsThe wellbore can be deflected from its
current position using any of the following:WhipstocksJetting bitBent subs with downhole motors
WhipstocksWhipstocksAdvantages•It provides a controlled hole curvature at the onset•Can be run at any depth in any kind of rock and very useful in hard rock where others failDisadvantage•It is necessary to drill the pilot hole and then trip out to change the smaller bit to one of the wellbore diameter.
Jetting bitJetting bitAdvantages•Several attempts can be made to initiate deflection without pulling out of hole •A full gauge hole can be drilled from the beginningDisadvantage•The technique is limited to soft-medium formations•Severe dog-legs can occur if the jetting is not carefully controlled•On smaller rigs there may not be enough pump capacity to wash away the formation
Bent subs with downhole motorsBent subs with downhole motorsThe bent sub is run directly above the motor and its
pin is offset at an angle of 1 – 3 degrees.Deflection of the wellbore occurs when drilling is
carried out with no surface rotation to the drillstring.The drill bit is forced to follow the curve of the bent
sub.The degree of curvature depends largely on the bent
sub offset angle and the OD of the motor.When the required angles (inclination and/or
azimuth) are obtained, this BHA is tripped out to be replaced with a rotary assembly.
Steerable motorsSteerable motorsThe motor is designed with an in-built bent housing
below the motor section; usually the connecting rod housing.
The bent housing angle is usually 0.25 – 1.5 degrees.
The use of steerable motors with the correct drill bit and BHA reduces the number of round trips required to produce the desired inclination/azimuth.
It can be used in either :Oriented mode (sliding)Rotary mode
Oriented (Sliding) mode•The drillstring remains stationary (rotary table or top-drive is locked) while the drill bit is rotated by the motor.
•The course of the well is only changed when drilling in sliding mode as the drill bit will now follow the curvature of the motor bent housing.Rotary mode•Steerable motor becomes “locked” with respect to trajectory and the hole direction and inclination are maintained while drilling.
Bit offset: Steerable motor vs. PDM with bent sub
Mud MotorsMud Motors
There are two types of mud motors:Turbines Positive displacement motors (PDM)
Turbine motorTurbine motorThe turbine motor consists of:
A multistage blade-type rotor and stator sections. The number of rotor/stator sections can vary from 25 to 50.
A thrust bearing section and a drive shaft. The rotor blades are connected to the drive shaft
and are rotated by mud pumped under high pressure.
The stator deflects the mud onto the rotor blades.Rotation of the rotor is transmitted to the drive
shaft and drill bit.
Positive displacement motors (PDM)Positive displacement motors (PDM)A PDM consists of:
Power section (rotor and stator) By-pass valve Universal joint Bearing assembly
Power sectionThe PDM consists of a helical steel rotor fitted
inside a spirally-shaped elastomer moulded stator.
Mud flowing under pressure fills the cavities between the dissimilar shapes of the rotor and stator and under the pressure of mud, the rotor is displaced and begins to rotate.
The rotor actually moves in an elliptical shape. This eccentric movement is converted to true circular motion by a universal joint assembly.
By-pass valveThis valve allows the drilling fluid to by-pass
the mud motor allowing the drillstring to fill during tripping in and drain when making a connection or pulling out of hole.
The valve operates by a spring which holds a piston in the upper position. In this position, ports in the by-pass valve are
open allowing mud to flow in or out of the drillstring.
At 30% of recommended flow rate, the piston is forced down, closing the ports and directing flow through the mud motor.
Universal Joint: A Connecting Rod assembly is attached to the
lower end of the rotor. It transmits the torque and rotational speed
from the rotor to the drive shaft and bit. Universal joints convert the eccentric motion
of the rotor into concentric motion at the drive shaft.
Bearing and Drive Shaft Assembly The drive shaft is a rigidly-constructed hollow
steel component. It is supported within the bearing housing by
radial and axial thrust bearings
Types of Well Profile Types of Well Profile Type I
Build and HoldType 2
Build, Hold and Drop.Returns to vertical after dropping – S-shape.Does not return to vertical after dropping –
Modified S-shape.Type 3
Continuous Build
KOP
TYPE IIITYPE IITYPE I
BUILD & HOLD BUILD – HOLD & DROP CONTINUOUS BUILD
Type I – build and holdType I – build and holdInformation needed:
Surface co-ordinates
Target co-ordinates
TVD of targetTVD to KOPBuild-up rate
Type II – build, hold and dropType II – build, hold and dropInformation needed:
Surface co-ordinates
Target co-ordinatesTVD of targetTVD to KOPTVD at end of drop-
off (usually end of well)
Build-up rateDrop-off rateFinal angle of
inclination through target.
Because Type II have 2 curves, 2 radii need to be calculated and compared with the total departure, D3.
These quantities are then used to calculate the maximum possible inclination angle at end of build-up curve.
D3 > (R1 + R2)
D3 < (R1 + R2)
Type III – continuous buildType III – continuous buildUsed for salt dome
drilling.For planning
appraisal wells.Information needed:
Surface co-ordinates
Target co-ordinatesOne parameter
from:Maximum
inclination angleTVD to KOPBuild-up rate
Design a directional well with the following restrictions:
• Total horizontal departure = 4,500 ft
• True vertical depth (TVD) = 12,500 ft
• Depth to kickoff point (KOP) = 2,500 ft
• Rate of build of hole angle = 1.5 deg/100 ft
• Profile type: Type I well (build and hold)
(i) What is the maximum hole angle required.
(ii)What is the total measured depth (MD)?
ft820,35.1
000,18r1
0r2
ft000,10
500,2500,12
DD 14
ft500,4x4
Maximum Maximum Inclination Inclination
AngleAngle
46
500,4)820,3(2
500,4)820,3(2000,10500,4000,10tan 2
221-
3.26max
421
4212
1424141
max x)rr(2
x)rr(2)DD(xDDtan2
47
ft 395
)26.3 cos-3,820(1
)cos1(rx 1Build
ft 4,105
395500,4xHold
ft 265,9L
105,4sinL
Hold
Hold
Measured Depth Measured Depth of Wellof Well
48
Holdrad11 LrDMD
ft 518,13MD
265,9180
26.33,8202,500