Directional & Horizontal Drilling

8/7/2019 Directional & Horizontal Drilling

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Directional &

Horizontal Drilling


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Directional Drilling

There's a maxim in drilling that says "there's no such thing as a

straight hole."

All wells, whether by accident or by design, exhibit changes in

hole angle and direction.

Crooked hole tendencies were considered early as a serious

drawback to the widespread use of rotary rigs. But the benefits of

rotary drilling were more than sufficient to overcome this

perceived limitation

So the industry began developing ways to keep wells on course.

Thus was born the science or, perhaps more accurately, the art of

deviation control.


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Definition of Directional Drilling

Directional drilling can be defined as

Science of directing a wellbore along apredetermined trajectory to intersect a

subsurface target.


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Applications of Directional Drilling

Offshore Multi-well Drilling

Relief Wells

Inaccessible Locations

Fault Controlling

Salt Dome Drilling

Sidetracking Horizontal Wells

Controlling Vertical Wells

Horizontal Wells


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Offshore Multi-well Drilling

A single directional well intersect several inclined oil reservoirs

Well may have to enter the targets at specific angle to ensure maximum

penetration of the reservoir

The wells are directionally drilled submersible rig and tied back to platform

once it has been installed


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Relief Wells

Objective is to intercept the borehole of a well for killing purpose

These wells are deviated to pass as close as possible to the

uncontrolled wells

Heavy mud is pumped into the reservoir to overcome the pressure

and bring the wild well under control


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Inaccessible Locations

For targets located beneath city, river etc

Directional well is drilled to reach the target


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Fault Drilling

Bits change direction due to faulted subsurface formations

Faults can slip and shear the casing


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Salt Dome Drilling

Severe drilling problems while drilling through salt formations

Directional well is drilled to reach the reservoir, thus avoiding theproblems associated to drilling salt dome

Another solution is to use salt saturated mud


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Sidetracking

Objective is to get past a fish or

to sidetrack a dry hole to more promising target or

to explore the extent of a producing zone in a certain sector ofa field


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Controlling Vertical Wells

Directional wells are drilled to straighten vertical wells


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Horizontal Wells

Increase productivity of various formations

More exposure to the reservoir


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Types of Directional Wells

Type 1: Build and Hold-- this patternemploys a shallow initial deflectionand a straight-angle approach to thetarget. Its used to reach single targetsat moderate depths, and sometimes fordrilling deeper wells with large

horizontal departures.

Type 2: Build, Hold and Drop -- after arelatively shallow deflection, thispattern holds angle until the well hasreached most of its required horizontaldisplacement. This pattern is mostapplicable to wells exposing multiplepay zones, or wells subject to target orlease boundary restrictions.


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Types of Directional Wells

Type 3: Continuous Build-- unlike the

Type 1 and 2 patterns, this trajectory

has a relatively deep initial deflection,

after which angle is maintained to the

target. The continuous build pattern is

well-suited to salt-dome drilling, fault

drilling, sidetrack sand redrills.

Type 4: Build, Hold and Build-- this is

the general pattern describing horizontal

wells. The decision to drill horizontally

is primarily based on reservoir

engineering and reservoir management

considerations.


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Deflection Tools

Downhole MudMotors

Directional wedges

Jet bits with oriented

nozzles


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Deviation in Vertical Wells - Causes

Following are the contributing factors for wellbore deviation

Formation

- Type, lithology

- Anisotropy

Bottom hole assembly size, configuration

- Stabilizers size, type & positioning

- Drill collars & Reamers

Drilling parameters

- Weight on bit

- Hydraulics

Bit type & Design features


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Deviation Control Methods

Wellbore deviation can be controlled by

Using pendulum assembly, consisting of the bit, drill collars and

strategically positioned stabilizers, to decrease hole angle (i.e.,

straighten the hole)

Using packed hole assemblies, consisting of reamers, short collars

and stabilizers, or square drill collars, to "lock in" the bit and maintain

a constant hole angle

Using directional drilling tools (e.g., downhole motors with bent

housings)


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Horizontal Drilling Horizontal drilling is the process of directing part of a well course

through a reservoir such that its inclination angle is approximately90 from vertical

Horizontal section may be anywhere from a few feet to thousands offeet in length.

Horizontal drilling begins with a more-or-less vertical surface section,followed by a bend section which progresses from approximately 0to 90 inclination with depth, and finally by a horizontal or lateralsection


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Horizontal Drilling Applications

Reservoirs that would otherwise be

economically inaccessible

For new development wells

Enhanced oil recovery


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Well ConfigurationLong radius build rate between 1o and 6oper 100 ft

build radius 1000 ft

Applications

multiple, extended-reach wells

exploratory wells over long intervals

wells that require zone isolation and

selective completion/stimulation

Medium radius build rate between 6o and 30oper 100 ft

build radius ranges from about 300 up to

1000ft

Applications

re-entry wells

reef reservoirs

fractured reservoirs

reservoirs with potential for gas or water

coning


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Well Configuration

Short radius build rate between 1o and 3o degrees per

foot

build radius 50 feet or less

Applications

infill drilling in depleted reservoirs

shaly intervals or other trouble-proneformations

multiple drain holes

enhanced oil recovery

Ultra-short radius no bend section

Applications

soft, unconsolidated formations

multiple drain holes from existingvertical wells

Documents

Directional & Horizontal Drilling