A new two-phase model to simulate sour gas kicks in MPD operations with Water Based Mud

Abstract

This study presented a new two-phase model for sour gas kicks in vertical well, which could be used to improve the bottomhole pressure estimation during a managed pressure drilling (MPD) operation. The model considered sour gas solubility in water based mud (WBM), by using Peng Robingson equation of state (EOS) to predict the PVT behavior of the WBM with dissolved gas. A test loop and full-scale experimental data from the published literature were both used to validate the model. The objective of the study was to develop a model to predict the annular pressure, and outlet flow rate during an MPD well control, to help deciding whether to shut the well in.The simulated results showed that in vertical wells with sour gas and WBM, as the percentage of H2S in total gas increased, the maximum pit gain/casing pressure both decreased while the maximum casing shoe pressure remained almost the same. The peak value of casing pressure appeared later than the moment that gas front migrated to the wellhead. Moreover, the effects of degrees of choke opening on the annular pressure during the MPD well control operations were analysed. The quantitative research has certain guiding significance to improve safety operation of MPD for sour gas reservoir development with lower non-productive time (NPT).