Directional Drilling
Directional Drilling
Directional Drilling
- Overview :
Controlled directional drilling is the engineering
process of planning and drilling a well
It is a drilling method in a predetermined trajectory,
until reaching a target or objective situated off of the
vertical line that passes thorough the rig
Directional drilling started as corrective operations for
some problems occurring during drilling such as:
Sidetracks due to fishing operation failures or
Extreme borehole tortuosity
Directional Drilling
- Overview :
Today, however, the applications of directional wells
in the industry are manifolds
Most recent advances include the drilling of horizontal
wells and multilateral wells, have revealed extremely
efficient in increasing the productivity of reservoirs
with small thickness
Directional Drilling
- Overview :
Among the most important uses of directional wells
is the development of offshore fields
The cost of the development of those fields using
vertical (conventional) wells would have made their
exploitation prohibitive
Directional Drilling
Directional Drilling
- Application of Directional Drilling :
Inaccessible locations:
Natural or artificial barriers preclude the access
from the vertical of the target
Relief wells:
Technique used to combat a blowing up well
The relief well reaches an area close to where the
gas is entering the well and mud with adequate
weight is pumped to kill the well
Directional Drilling
- Application of Directional Drilling :
Natural directional wells:
Use the natural tendency of certain formations
to reach the target with lower cost
(vertical too expensive)
Horizontal wells:
In thin formations, horizontal wells increase the
area exposed to flow, increasing production
Directional Drilling
- Application of Directional Drilling :
Sidetrack:
Change in the original trajectory due to pieces of
metal or fishes that could not be recovered by
fishing operation
Sidetracks are not planned in advance, but the
equipment and techniques are the same used
in directional drilling
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Directional Drilling
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Directional Drilling
- Application of Directional Drilling :
Environmental pressures, as for example in Alaska
and in the Amazon, have increased the use of
onshore directional drilling
Directional drilling is also used in the development
of geothermal projects
Geothermal reservoirs can reach temperatures of
370oC, and are used to generate steam from water
pumped from surface
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Directional Drilling
- Well Trajectory Local Coordinate System:
The planned and drilled trajectories of a directional
well are either 2D or 3D objects
Associated to any point along the trajectory
(planned or actual) there are
three values that can be determined (planned
trajectory) or measured (actual trajectory)
Those values can be used to determine the
coordinates of the point in the rig local coordinate
systems
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Directional Drilling
- Well Trajectory Local Coordinate System:
The values are :
Measured Depth
Inclination
Azimuth
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Directional Drilling
- Well Trajectory Local Coordinate System:
The measured depth at the point of the trajectory
is the measured of the length along the trajectory,
from the rotary table to the point
Therefore, the measured depth is not, in fact, a
depth in the strict sense of the word but a length
(unless for a perfectly straight vertical trajectory)
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Directional Drilling
- Planning a 2D Directional Well Trajectory :
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Directional Drilling
- Planning a 2D Directional Well Trajectory :
The location of the rig determines the rig local
coordinate system
The rig and the target determine a vertical plane
which contains the vertical V, and the target T
It is on this vertical plane that the directional well
trajectory is planned drawn
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Directional Drilling
- Planning a 2D Directional Well Trajectory :
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Directional Drilling
- Planning a 2D Directional Well Trajectory :
Point R corresponds to the rig location, and also
the origin of the rig local coordinate system
Point T is the target, whose coordinates (v, n, e)
are respectively the TVD, relative North/South,
and relative East/West coordinates of the target
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Directional Drilling
- Planning a 2D Directional Well Trajectory :
The distance d from the target to the vertical axis V
is called the horizontal departure to target and is
calculated from the relative coordinates n and e as
follows:
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Directional Drilling
- Planning a 2D Directional Well Trajectory :
The target azimuth is the angle of the vertical
plane and is given by:
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Directional Drilling
- Planning a 2D Directional Well Trajectory :
The parameters v (TVD) and horizontal departure
d are the basic parameters we need to plan the 2D
trajectory of the directional well
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Directional Drilling
- Terms for Well Trajectory :
When drilled from conventional rigs, a directional
well trajectory starts with a vertical hole section
drilled to a given depth where it starts to curve
This point is called kick-off point (KOP) and its
determination depends on various factors,
in particular, the mechanical competence and
stability of the formation where the curved section
(and the angle) starts to build
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Directional Drilling
- Terms for Well Trajectory :
A too soft formation will not support the lateral
force required to drive the bit into a curved path
A too hard formation will resist to the effects of the
deviation tool
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Directional Drilling
- Terms for Well Trajectory :
The position of the KOP will also affect the final
and/or the maximum inclination of the trajectory
The engineer, therefore, will have to simulate
several trajectories and choose the one that best
fits the characteristics of the region to be drilled
Some restrictions on the trajectory will narrow the
range of possibilities
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Directional Drilling
- Terms for Well Trajectory :
For example, the ideal or necessary angle to reach
the target :
To drill the reservoir perpendicular to the plan of
highest permeability in anisotropic rocks, or
Perpendicular to the fractures of a naturally
fractured reservoir
Parallel to a blowing out well to more efficiently
kill the well
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Directional Drilling
- Terms for Well Trajectory :
The hole section that follows the KOP is called
build-up section
It is always recommended to run a casing shortly
after the end of the build-up section
A cased borehole will prevent the formation of key
seats which may lead pipesticking problems
Since casing projects should follow several design
criteria, it is appropriate, and advisable, that
engineers work as an integrated team aiming to
end up with a small number of optimized plans
that comply with all design criteria
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Directional Drilling
- Terms for Well Trajectory :
The final choice will consider economics, logistics
(availability of deflection tools at or close to the
location, etc)
The experience of the team will also play an
important role, reducing substantially the number
of interactions required to obtain the optimal plans
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Directional Drilling
- Geometric Elements of 2D Well Trajectories:
The simplest curved segment used in trajectory
planning is the sector of circle
An advantage is that only one parameter is
required to define the curve
One such parameter is the radius of the circle R
Instead of specifying the radius R, it is possible to
specify its inverse c, or curvature
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Directional Drilling
- Geometric Elements of 2D Well Trajectories:
The radius and the curvature are related by
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Directional Drilling
- Geometric Elements of 2D Well Trajectories:
The curvature can be expressed as:
A length L of a circle of radius R subtend an angle
such that L = R for in radians
C: rad/min
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Directional Drilling
- Geometric Elements of 2D Well Trajectories:
The radius can be calculated by:
for c in degrees per length
Common units of curvature are degrees per 100 ft, and
degrees per 30 m
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Directional Drilling
- Geometric Elements of 2D Well Trajectories:
It is common also to refer to curvature as :
buildup rate
(BUR for building angle curves)
dropoff rate
(DOR for dropping angle curvatures
doglegseverity
(DLS for curves in general, and in particular to
measure the degree of tortuosity of a trajectory)
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Directional Drilling
- Geometric Elements of 2D Well Trajectories:
The TVD and the horizontal departure are the basic
parameters needed to plan a 2D trajectory for a
directional well
All other parameters are set by the engineer, or are
calculated
The degree of freedom of a trajectory type is the
number of independent parameters we need to set
in order to calculate the remaining parameters
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Directional Drilling
- Geometric Elements of 2D Well Trajectories:
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2D Trajectory Geometries
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Directional Drilling
- Classifying 2D Well Trajectories:
Build and Hold
Build, Hold, and Partial Drop (Modified S type)
Build, Hold, and Drop ( S type)
Continuous Build
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Directional Drilling
- Classifying 2D Well Trajectories:
Build and Hold (Profile A):
Drilling starts vertical to the KOP
From this point angle starts to build (build up
segment) until a maximum inclination is reached
(end of build)
Drilling continues with a straight segment (slant)
until reach the target
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Directional Drilling
- Classifying 2D Well Trajectories:
Build and Hold (Profile A):
The Build and Hold type has three parameters
and two degrees of freedom:
KOP
BUR
Maximum Inclination
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Directional Drilling
- Classifying 2D Well Trajectories:
Build and Hold (Profile A):
Determine KOP given BUR and max
(Max.Inclination)
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Directional Drilling
- Classifying 2D Well Trajectories:
Build and Hold (Profile A):
Determine KOP given BUR and Max. Inclination
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Directional Drilling
- Classifying 2D Well Trajectories:
Build and Hold (Profile A):
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Directional Drilling
- Classifying 2D Well Trajectories:
Build and Hold (Profile A):
Determine max given KOP and BUR
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Directional Drilling
- Classifying 2D Well Trajectories:
Build and Hold (Profile A):
Determine max given KOP BUR and
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Directional Drilling
- Classifying 2D Well Trajectories:
Build and Hold (Profile A):
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Directional Drilling
- Classifying 2D Well Trajectories:
Build and Hold (Profile A):
Determine BUR given KOP and max
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Directional Drilling
- Classifying 2D Well Trajectories:
Build and Hold (Profile A):
Determine BUR given KOP and max
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Directional Drilling
- Classifying 2D Well Trajectories:
Build and Hold (Profile A):
Determine BUR given KOP and max
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Directional Drilling
- Classifying 2D Well Trajectories:
Build and Hold (Profile A):
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Directional Drilling
- Classifying 2D Well Trajectories:
Build, Hold, and Drop (profile C):
Drilling starts vertical to the KOP
From this point angle starts to build (build up
segment) until a maximum inclination is reached
(end of build)
Drilling continues straight (slant segment) until
a point called DOP (drop-off point) is reached
From this point, angle decreases (drop-off
segment) until it becomes vertical (end of drop)
From this point, drilling continues vertical until
reach the target
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Directional Drilling
- Classifying 2D Well Trajectories:
Build, Hold, and Drop (profile C):
The Build and Hold type has five parameters and
four degrees of freedom:
KOP
BUR
Maximum Inclination
DOR
EOD (vertical depth of the endof-drop)
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Directional Drilling
- Classifying 2D Well Trajectories:
Build, Hold, and Drop (profile C):
Determine max given KOP, BUR (c1), DOR (c2),
and EOD
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Directional Drilling
- Classifying 2D Well Trajectories:
Build, Hold, and Drop (profile C):
Determine max given KOP, BUR (c1), DOR (c2),
and EOD
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Directional Drilling
- Classifying 2D Well Trajectories:
Build, Hold, and Drop (profile C):
The measured depth, true vertical depth, and
horizontal departure of the endofbuild (EOB)
section is given by
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Directional Drilling
- Classifying 2D Well Trajectories:
Build, Hold, and Partial Drop (profile B):
Drilling starts vertical to the KOP
From this point angle starts to build (build up
segment) until a maximum inclination is reached
(end of build)
Drilling continues straight (slant segment) until a
point called DOP (drop-off point) is reached
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Directional Drilling
- Classifying 2D Well Trajectories:
Build, Hold, and Partial Drop (profile B):
From this point, angle decreases (drop-off
segment) until a given inclination is obtained
(end of drop)
From this point, drilling continues straight until each
the target
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Directional Drilling
- Classifying 2D Well Trajectories:
Build, Hold, and Partial Drop (profile B):
The Build, Hold, and Partial Drop type has six
parameters and five degrees of freedom:
KOP
BUR
maximum inclination
DOR
hang length - s
(sometimes the vertical depth of the EOD)
hang inclination (the inclination to reach the
target)
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Directional Drilling
- Classifying 2D Well Trajectories:
Build, Hold, and Partial Drop (profile B):
This is very similar to the BuildHoldDrop type
The difference is that the trajectory reaches the
target with a given angle (hang inclination)
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Directional Drilling
- Classifying 2D Well Trajectories:
Continuous Build (profile D):
Drilling starts vertical to the KOP
From this point angle starts to build in a relative
smaller rate (build up segment) until the drilling
reaches the target
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Directional Drilling
- Classifying 2D Well Trajectories:
In addition to these basic types, there exist other
special profiles
These profiles are more suitable to deep drilling
projects, extended reach wells (ERW), and
horizontal wells
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Directional Drilling
- Classifying 2D Well Trajectories:
Catenary:
The catenary type was proposed with the purpose
of minimizing the torque along the drillstring
It is a special case of the continuous build type,
but with a controlled variable curvature
It would represent the natural shape of a
drillstringsuspended at the rotary table and at the
target
Several operational problems put a lot of
difficultiesin this type of trajectory
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Directional Drilling
- Classifying 2D Well Trajectories:
Double Build:
This type is very common in horizontal drilling
It is an analogous of the build, hold, and drop, but,
instead of dropping to the vertical, the second
curved segment is another build, ending at the
inclination of 90o
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Directional Drilling
- Classifying 2D Well Trajectories:
Reverse Double Build:
To extend the horizontal section for pay zones not
too far from the rig position, a reversed double
build type is used
In this kind of trajectory, the first curved segment
is
built in a direction opposite to the target, so to
increase the departure of the target
Then a second build segment starts, dropping
back
to vertical and continuing building angle, now in the
direction of the target
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