For economic and technical reasons, the industry has used directional, extended-reach, horizontal, and multilateral wells. Although technologies are well developed for these wells, and there are numerous successes in the last decade, these wells still have high level of risk in drilling and completion. Well control is one of the relatively unanswered, but important, operations because improper well control, followed by a blowout is one of the most expensive and feared operational hazards.
To maintain a specified bottomhole pressure (BHP), surface choke pressures highly depend on kick vertical height in the well and well trajectory. As the final hold angle of the well increases from vertical, shut-in casing pressure (SICP) reduces to shut-in drillpipe pressure (SIDPP) and remains the same as long as the kick stays in the horizontal section. For equal vertical depths, the maximum choke pressure is insensitive to hold angles or hold lengths, aslong as the initial pit-volume gain is the same. However, for directional andextended-reach wells, choke pressure can increase, even without kick expansion, because of the gain of kick vertical height in the build section. This may maskchoke-pressure reduction because of larger annular capacity when the kick passes the casing shoe, especially if the kickoff point (KOP) and casing-shoe depth are close.
In multilateral wells with more than one kicking wellbore, SIDPP is affected by both formation over pressure and kick size in each wellbore. The maximum value among them will appear at the surface. Therefore, we should be careful in the interpretation of the shut-in pressures. For safe kick circulation, we must consider additional pressure to compensate for hydrostatic-pressure reduction resulting from kick migration and expansion in branch wellbores.