Study on Rising Velocity of Methane Bubble in Deepwater Wellbore During the Shut-In Period

Abstract

Abstract The formation of hydrate membrane on the methane bubble surface could occur in the high pressure & low temperature wellbore during the shut-in period. Using an empirical drag coefficient model to investigate the laws of methane bubble with hydrate membrane rising in drilling mud is important for calculating the well control safety operation cycle time in avoiding typhoon. The drag coefficient for methane bubble with hydrate membrane rising in mud within a wellbore was experimentally investigated using a vertical, cylindrical wellbore with high pressure & low temperature. A high-speed camera was used to obtain the process of methane bubble with Methane hydrate membrane (MHM) rising under 6 MPa & 4 °C. The velocities of bubbles were measured by image processing software. The drag coefficients of different bubbles were calculated and the variation law of drag coefficient with Reynolds number was obtained. A new correlation of drag coefficient for the bubbles covered with hydrate membrane is established. The result of experiment indicated that the rising velocity of methane bubble with hydrate membrane would increase along with the increase of equivalent diameter, while drag coefficient would decrease before increase along with the increase of equivalent diameter. Due to the influence of hydrate membrane, the rising process of methane bubble covered with hydrate membrane would be significantly different from that of pure gas bubble; compared with pure gas bubble, the methane bubble of same diameter would have lower rising velocity. Through the comparison with known correlation of drag coefficient, it is believed that the existing drag coefficient correlations are not applicable to the prediction of drag coefficient of methane bubble covered with hydrate membrane. A new correlation of drag coefficient of rising methane bubble covered with hydrate is established, such correlation has scope of prediction error within ±25%. Considering the influence of hydrate membrane, a new rising velocity model for methane bubble covered with hydrate membrane is established to calculate the drag coefficient.