Evolution of gas kick and overflow in wellbore during deepwater drilling and advantage analysis of early gas kick detection in riser

Key words:  deepwater drilling  gas kick and overflow  mud pit gain  early gas kick detection  riser

Abstract:

For oil and gas well-drilling in deepwater and ultra deepwater, the idea of making use of the advantage of the long length of the riser to monitor gas kicks at the bottom of the riser has become one of the hot spots for research. In this study, the flow and migration gas in wellbore were analyzed, considering the effects of water depth, drilling depth below the mud line, bottom hole pressure difference, formation permeability, and a two-phase flow model of gas-liquid in wellbore was established. The simulation results indicate that monitoring of the gas kicks at the bottom of the riser is more effective than that using the conventional mud level method in deepwater drilling under the conditions of water depth greater than 800 m, the drilling depth less than 2800 m below the mud line, and the formation permeability less than 50×10-3 μm². Moreover, the deeper the water depth, the less of the drilling depth below the mud line and the smaller of the formation-bottom hole pressure difference, the more effective of the riser monitoring technique.