Well Control – Initial Circulating Pressure on deepwater
On deepwater drilling, the subsea bop stack is installed at the well head (on sea bed). In kick condition, the BOP is closed and the flux is deviated to the choke at surface through the choke line. This line has a diameter normally of 3 inches and the frictional pressure losses will increase the pressure at shoe depth. This is a big problem on deepwater wells due to the formation pressure be fragile.
A method to compensate the choke line friction is to decrease the initial choke pressure of this value, monitoring the annulus pressure at the kill pressure gauge instead the choke pressure gauge when bringing the mud pump to slow circulation rate, like on a surface bop well control, and adjusting the choke to set the drill pipe pressure equal to the Initial Circulating Pressure (ICP) calculated by the formula ICP = SIDPP (Shut-in Drill Pipe Pressure) + Pump Pressure @ slow circulating rate when circulating through the drill string with return to the riser.
- Why to use the pump pressure with return to the riser if the circulation of the kick is with return to the choke?
- Why to set the choke fully open during the circulation to record the choke line friction?
The answers for these questions are in the calculations in the next slides.
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