Page 286 - Well Control for Completions and Interventions

Well Kill, Kick Detection, and Well Shut-In 279

with mud in the hole, a bullhead will almost always result in the fractur-
ing of the formation.

7.4.1 Before a bullhead kill
In planning to kill the well by bullhead, there are several important con-
siderations that can only be properly assessed if some essential information
has been obtained. This will include, but need not be limited to:
• Formation fracture pressure. If the kill is prior to final abandonment
of the well, the fracture pressure of the cap rock may be used.
• Reservoir pressure.
• SITP.
• Tubing fluid density, including oil water contact and GOC if known.
• Annulus fluid density and fluid level.
• Reservoir injection potential. Estimate or establish the maximum
injection rate (bbls/min) that is achievable at below formation fracture
pressure:
• Theoretical values based on completion architecture, reservoir
geometry, reservoir permeability, and fluid characteristics using
inflow performance models such as “Prosper.” Hand calculations
can also be used.
• Empirical data: in some fields, chemical treatments (scale and cor-
rosion inhibitors) are routinely “squeezed” into the reservoir by
bullheading down the completion.
• Injection test: if no empirical data is available, and there are con-
cerns about the validity of theoretical assumptions, an injection test
should be performed, preferably in advance of the planned
intervention.
• LCM: since a bullhead kill requires the formation to have good per-
meability, losses will occur when the well is filled with a clear, solids-
free fluid that overbalances the formation. LCM will be needed to
control losses after killing the well and can be pumped ahead of the
kill fluid. LCM must be non-damaging, and compatible with the for-
mation, reservoir fluids, and the completion equipment. In wells fitted
with sand control screens, the LCM should be sized to bridge off
across the inside of the screens and not the formation.
• Completion design limitations:
• If the completion tubing is anchored to a packer, axial tension will
increase during the bullhead due to a combination of thermal