Time-dependent gas dissolution on kick migration during deepwater drilling

Gas dissolution–desolution dynamics during drilling operations induce complex kick migration patterns, posing significant challenges to early kick detection and wellbore pressure management. In this study, a theoretical model of gas solubility in drilling fluids is proposed, incorporating the complex interactions between gas, salts, polymers, and base oil under different temperature and pressure conditions. Experimental validation demonstrates mean errors of 3.487% and 6.751% for water-based (WBDFs) and oil-based (OBDFs) drilling fluids, respectively. Considering time-dependent gas dissolution, a wellbore multiphase flow model is developed to characterize dynamic kick migration in the wellbore. Simulations indicate that gas dissolution slows the rate of change in pit gain and bottomhole pressure (BHP), resulting in concealed gas influx in deepwater drilling. A comparative analysis revealed that OBDF exhibits a slower pit gain and BHP response, with gas kick detection time 1.57 times longer than that in WBDF. During well shut-in, the gas influx predominantly remains dissolved in OBDF, causing BHP to generally stabilize at formation pressure. To mitigate gas influx desolution and expansion effects, a minimum wellhead backpressure of 5 MPa is recommended.