Page 289 - Well Control for Completions and Interventions

282 Well Control for Completions and Interventions

formation fracture pressure minus the HP of the reservoir fluids in the
tubing. A safety margin is normally applied.
The maximum surface pump pressure at the beginning of the kill for-
mation fracture limit is

Initial pump pressure ðfracture limitÞ 5 formation fracture pressure
hydrostatic pressure to top reservoir safety margin
The safety margin varies, depending on location and company policy,
but is normally between 100 and 500 psi. A common error when calcu-
lating the maximum pressure at the start of the kill is to include wellhead
closed-in pressure with the hydrostatic calculation. This is a mistake and
unnecessary, since no kill fluid can enter the well until pump discharge
pressure is equal to or more than wellhead closed-in pressure.

4 Calculate the maximum surface pump pressure (formation fracture
limit) at the end of the kill
At the end of a bullhead kill, the pressure acting on the formation is the
HP of the kill fluid in the tubing (from the surface to the top reservoir)
plus any applied surface pressure (pump pressure). The maximum (pump
discharge) pressure that can be applied at the surface is formation fracture
pressure minus the HP of kill fluid in the tubing. A safety margin is
normally applied.
The maximum surface pump pressure at the end of the kill formation
fracture limit is:

Final pump pressure ðfracture limitÞ 5 formation fracture pressure
kill weight fluid hydrostatic pressure at top reservoir safety margin

5 Tubing burst limit
Use 80% of the API burst limit.

6 Calculate maximum pump pressure (tubing burst mechanical limit)
at the start of the kill
At the start of the kill, the highest pump pressure than can be applied at
surface is tubing burst limit, minus the HP of the hydrocarbon fluids in
the tubing at packer depth. This is a worst-case assumption, and makes
no allowance for the HP in the annulus.