Experimental Investigation on the Effect of Methane Solubility in Oil-Based Mud Under Downhole Conditions

Accurate prediction of CH4 solubility in oil-based mud is significant for evaluating gas kick severity and implementing proper well control. The main factors affecting gas solubility in oil-based drilling fluid are base oil content, pressure, temperature, drilling fluid viscosity, and the components in natural gas. This work tests the complete series of solubility of high-purity CH4 in oil-based mud simulating downhole conditions on a 5,000-m-deep well relative to temperature, pressure, viscosity, and base oil content with temperature ranging from 40°C to 140°C and pressure ranging from 2 to 56 MPa using a PVT autoclave. Then, the effects of temperature, pressure, base oil content, and drilling fluid viscosity on the test target are analyzed using multiple experimental data processing methods. It is found that the variation of methane solubility with pressure and temperature are almost linearly under interested ranges. The effects of pressure (0.205 to ~0.294%/MPa) are much higher than that of temperature (–0.008 to –0.011%/°C) in oil-based drilling mud; the solubility of methane decreases as viscosity increases. Models for predicting methane solubility have been developed using screening procedures and statistics regression, which can be integrated into gas-liquid flow models to investigate flow behavior while gas kicking.