In deepwater dual-gradient wells, if gas comes into the riser, a rapid unloading event may occur if removal of the gas is not carried out properly. Oil-based muds (OBMs) present an even greater challenge when compared with water-based muds (WBMs) to avoid gas in riser events. A study using a dynamic multiphase-flow software simulated a rapid-unloading event and determined the gas fraction in the riser annulus and the effect on riser fluid levels.
Case Description and Model Verification
Several researchers have run field tests to study rapid unloading of gas in deepwater risers. These tests used WBMs; there are no comparable data from tests using OBMs.
Previous papers described the results from field tests of procedures for handling various well-control scenarios in a dual-gradient drilling application.
