Movement features of gas in different types of drilling fluid during kicking in deepwater wells

The drilling fluids for deepwater drilling can break down the formations easily during well killing for its density window is generally less than 0.06 g/cm3. In order to perform well control accurately in time, it is necessary to study the movement features of gas in different types of drilling fluid. After multiphase flow was theoretically analyzed and calculated, the results were checked by using the Drillbench Software based on drilling fluid and actual drilling data of two wells. In this way, the movement features of gas in different types of drilling fluid were identified. The gas in water-base drilling fluid is presented in the form of slippage and expansion, and it can break the upper casing shoe after long-term well shut in. In oil-base or synthetic-base drilling fluids, the gas is dissolved and then migrates out when the bubble point pressure is reached. It is easier to detect the kick in water-base drilling fluid than in oil-base drilling fluid, for the gas is dissolved into the latter one. This paper strengthens the understanding on the deepwater well control and provides the theoretical basis for deepwater well design and safe well control operation.