A study of rapid increasing choke pressure method for sour gas kicks during managed pressure drilling

The numerical simulation of rapid increasing choke pressure method for complete sour gas kick circulations is achieved, by using a transient, multiphase flow model, which has been verified with full-scale kick experimental date. The results indicate that the bottomhole pressure change rules can be classified into four cases based on the behaviour of the key parameter, which is choke pressure increment (ΔPc). Each case follows the identical four phases. Perfect well control procedure can be achieved by accurately adjusting ΔPc. A new method is proposed that could determine more precisely whether the formation flow ultimately stops by comparing the values between two points from bottomhole pressure or from standpipe pressure. The appropriate ΔPc interval can be also ascertained by combining with safe mud density window. The rapid increasing choke pressure method could effectively inhibits the dissolved H2S from releasing and greatly reduce the gas expansion and resulting pressure fluctuation near the wellhead, thus it is quite suitable for sour gas development with low-high H2S content. [Received: May 20, 2014; Accepted: December 13, 2014]