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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