Gas kick simulation in oil-based drilling fluids with the gas solubility effect during high-temperature and high-pressure well drilling

The high solubility of the invaded gas in oil-based drilling fluids and the heat transfer between annulus fluids and the surrounding formation make the accurate prediction and effective control of the bottomhole pressure (BHP) difficult during deep well drilling. In this study, a transient gas-liquid two-phase flow model considering the gas solubility and heat transfer effects is developed to simulate multiphase flow behaviors after gas kick in oil-based drilling fluids. Finite difference method is adopted to solve the governing equations. Predicted wellbore temperature and pressure distributions are in good agreement with field data, which indicates the accuracy of this model. Based on the proposed model, the flowing and thermal behaviors of gas and liquid phases in the annulus are compared when the gas solubility effect and the heat transfer effect are incorporated and not incorporated into the model. In the case of this study, without considering the gas solubility effect, the bottomhole pressure could be underestimated by 4.2% (2.92 MPa), while the bottomhole temperature is overestimated by 3.2% (3.74 degrees C). Without considering the heat transfer effect, the bottomhole pressure could be overestimated by 11.4% (7.94 MPa) under steady flow conditions. Besides, the effects of the reservoir pressure difference, choke pressure, geothermal gradient, and well depth on the wellbore pressure and temperature distributions are investigated. The results of this study may help field operators to accurately predict and effectively control the bottomhole pressure after gas kick in oil-based drilling fluids during deep well drilling.