Post on 17-Dec-2015
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Directional Drilling
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Directional Drilling
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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
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- 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
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- 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
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- 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
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- 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
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- 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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- 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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- 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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- Well Trajectory Local Coordinate System:
The values are :
Measured Depth
Inclination
Azimuth
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- 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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- Planning a 2D Directional Well Trajectory :
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- 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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- Planning a 2D Directional Well Trajectory :
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- 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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- 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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- Planning a 2D Directional Well Trajectory :
The target azimuth is the angle of the vertical plane and is given by:
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- 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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- 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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- 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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- 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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- 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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- 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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- 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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- 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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- Geometric Elements of 2D Well Trajectories:
The radius and the curvature are related by
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- Geometric Elements of 2D Well Trajectories:
The curvature can be expressed as:
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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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- Geometric Elements of 2D Well Trajectories:
The radius can be calculated by:
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for c in degrees per length
Common units of curvature are degrees per 100 ft, and
degrees per 30 m
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- 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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- 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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- Geometric Elements of 2D Well Trajectories:
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2D Trajectory Geometries
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- 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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- 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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- 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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- Classifying 2D Well Trajectories:
Build and Hold (Profile A):
Determine KOP given BUR and max (Max.Inclination)
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- Classifying 2D Well Trajectories:
Build and Hold (Profile A):
Determine KOP given BUR and Max. Inclination
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- Classifying 2D Well Trajectories:
Build and Hold (Profile A):
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- Classifying 2D Well Trajectories:
Build and Hold (Profile A):
Determine max given KOP and BUR
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- Classifying 2D Well Trajectories:
Build and Hold (Profile A):
Determine max given KOP BUR and
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- Classifying 2D Well Trajectories:
Build and Hold (Profile A):
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- Classifying 2D Well Trajectories:
Build and Hold (Profile A):
Determine BUR given KOP and max
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- Classifying 2D Well Trajectories:
Build and Hold (Profile A):
Determine BUR given KOP and max
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- Classifying 2D Well Trajectories:
Build and Hold (Profile A):
Determine BUR given KOP and max
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- Classifying 2D Well Trajectories:
Build and Hold (Profile A):
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- 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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- 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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- Classifying 2D Well Trajectories:
Build, Hold, and Drop (profile C):
Determine max given KOP, BUR (c1), DOR (c2), and EOD
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- Classifying 2D Well Trajectories:
Build, Hold, and Drop (profile C):
Determine max given KOP, BUR (c1), DOR (c2), and EOD
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- 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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- 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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- 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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- 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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- 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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- 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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- 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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- 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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- 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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- 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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