Study on gas-liquid two-phase flow law considering gas dissolution during gas invasion in gas field drilling

Abstract

During the drilling and development of sour natural gas (including CO2 and H2S) fields, due to the high solubility of sour natural gas in drilling fluid, the concealment after gas invasion increases, resulting in well control accidents. Therefore, it is of great significance for gas field development to deeply study and understand the solubility of acid gas and the flow law of annular air and liquid after the gas invasion. In this paper, a multiphase flow equation considering gas dissolution is established. Based on the existing solubility experimental data, the equation of state for predicting the solubility of sour natural gas is optimized. It is found that the fugacity activity method using Peng and Robinson equation of state has the highest accuracy. The analysis of gas-liquid two-phase law through a specific example shows that considering the influence of gas dissolution, the increment of mud pit changes slowly and the concealment of gas invasion is strong. When the content of acid gas in drilling fluid is higher, the time for the pit gain change monitored on the ground increases and the concealment further increases, which is more harmful to the safety control of wellbore pressure.