drilling engineering - directional drilling

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-ordinatesTarget co-ordinatesTVD of targetTVD to KOPBuild-up rate

Type II – build, hold and dropType II – build, hold and dropInformation needed:

Surface co-ordinatesTarget 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-ordinatesTarget 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)?

θ

ft820,35.1

000,18r1 =

π=

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 =θ

−++−−+−−

=θ −

421

4212

1424141

max x)rr(2

x)rr(2)DD(xDDtan2

47

ft 395

)26.3 cos-3,820(1

)cos1(rx 1Build

==

θ−=

ft 4,105

395500,4xHold

=−=∴

ft 265,9L

105,4sinL

Hold

Hold

=∴=θ∴

Measured Depth of Measured Depth of WellWell

48

Holdrad11 LrDMD +θ+=

ft 518,13MD =

265,9180

26.33,8202,500 +

π+=