Types of Directional Patterns
The advent of steerable systems has resulted in wells that are planned and
drilled with complex paths involving 3-dimensional turns. This is
particularly true in the case of re-drills, where old wells are sidetracked and
drilled to new targets.
These complex well paths are harder to drill and the old adage that “the
simplest method is usually the best” holds true. Therefore, most directional
wells are still planned using traditional patterns which have been in use for
many years. Common patterns for vertical projections are shown on the following pages:
Features:·
Shallow kick-off point (KOP)
Build-up section (which may have more than one build up rate)
Tangent section
Applications:
Deep wells with large horizontal displacements
Moderately deep wells with moderate horizontal displacement, where intermediate casing
is not required
Features: There are several variations:
Shallow KOP - Build, hold & drop back to vertical
Build-up section - Build, hold, drop & hold (illustrated above)
Tangent section - Build, hold & continuous drop through reservoir
Drop-off section
Applications: Disadvantages:
Multiple pay zones - Increased torque & drag
Reduces final angle in reservoir - Risk of keyseating
Lease or target limitations - Logging problems due to inclination
Well spacing requirements
Deep wells with small horizontal displacements
Features:
Deep KOP
Build-up section
Short tangent section (optional)
Applications:
Appraisal wells to assess the extent of a newly discovered reservoir
Repositioning of the bottom part of the hole or re-drilling
Salt dome drilling
Disadvantages:
Formations are harder so the initial deflection may be more difficult to achieve
Harder to achieve desired tool face orientation with downhole motor deflection assemblies
(more reactive torque)
Longer trip time for any BHA changes required
On multi-well platforms, only a few wells are given deep kick-off points,
because of the small slot separation and the difficulty of keeping wells
vertical in firmer formation. Most wells are given shallow kick-off points
to reduce congestion below the platform and to minimize the risk of
collisions.
The advent of steerable systems has resulted in wells that are planned and
drilled with complex paths involving 3-dimensional turns. This is
particularly true in the case of re-drills, where old wells are sidetracked and
drilled to new targets.
These complex well paths are harder to drill and the old adage that “the
simplest method is usually the best” holds true. Therefore, most directional
wells are still planned using traditional patterns which have been in use for
many years. Common patterns for vertical projections are shown on the following pages:
Features:·
Shallow kick-off point (KOP)
Build-up section (which may have more than one build up rate)
Tangent section
Applications:
Deep wells with large horizontal displacements
Moderately deep wells with moderate horizontal displacement, where intermediate casing
is not required
Features: There are several variations:
Shallow KOP - Build, hold & drop back to vertical
Build-up section - Build, hold, drop & hold (illustrated above)
Tangent section - Build, hold & continuous drop through reservoir
Drop-off section
Applications: Disadvantages:
Multiple pay zones - Increased torque & drag
Reduces final angle in reservoir - Risk of keyseating
Lease or target limitations - Logging problems due to inclination
Well spacing requirements
Deep wells with small horizontal displacements
Features:
Deep KOP
Build-up section
Short tangent section (optional)
Applications:
Appraisal wells to assess the extent of a newly discovered reservoir
Repositioning of the bottom part of the hole or re-drilling
Salt dome drilling
Disadvantages:
Formations are harder so the initial deflection may be more difficult to achieve
Harder to achieve desired tool face orientation with downhole motor deflection assemblies
(more reactive torque)
Longer trip time for any BHA changes required
On multi-well platforms, only a few wells are given deep kick-off points,
because of the small slot separation and the difficulty of keeping wells
vertical in firmer formation. Most wells are given shallow kick-off points
to reduce congestion below the platform and to minimize the risk of
collisions.
