SUMMARY
With the increase of global deepwater drilling, the scale of the deepwater drilling contract market continues to expand, and the depth of the drilling operations constantly refresh the record. At the same time, the drilling environment and related geological conditions become more and more complex, which leads to the increase of the risk in the operation of deepwater drilling. After the happening of “Deepwater Horizon ” in the Gulf of Mexico, the prevention and control of blowout has become an urgent problem to be solved in the development of offshore oil and gas. Dealing with the problem of overflow and blowout in deepwater drilling, the most effective technical measures are early detection and identification of gas influx. The research on the degree of gas invasion is the basis of the formulation and implementation of well control measures. In this paper, a simulation model of gas-liquid twophase flow after the happening of gas influx is established to calculate the cross section gas content, mud tank overflow and bottom-hole pressure. Through the calculation, the real-time quantitative relationship between the characterization of the gas content and the bottomhole pressure and the increment of the mud pool was established and then the realtime quantitative degree of gas invasion is analyzed.