Abstract
Gas influx detection is one of the most important ways to improve well control safety. The responses of annular pressure while drilling (APWD) measurements have been used to provide a rapid and early warning of the development of gas influx. Considering the water hammer effect at the initial stage of gas influx, a new model has been established to describe the APWD pressure variation accurately. The accuracy of the mathematical model and the method for solution have been verified by a full-scale experiment. Combined with case analysis, the APWD pressure variations during gas influx under different conditions were simulated. Moreover, the probabilities of different APWD response patterns are presented. Calculation results show that the gas influx can be identified when the invaded gas volume is 0.5–0.8 m3.
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