Experimental study on the dissolution characteristics of ethane into oil-based mud in complex oil and gas wellbore environments

Abstract Accurate determination of ethane solubility in oil-based mud is significant to identify the gas kick severity and implementing proper well control procedures. The main factors affecting the ethane gas solubility in oil-based drilling fluid are base oil content, pressure, temperature, and the drilling fluid viscosity. This work tests the complete series of solubility of high-purity ethane in oil-based mud simulating downhole conditions on a 5000m deep well relative to temperature, pressure, viscosity and base oil content with temperature range 40 ℃ to 140 ℃ and partial pressure range 0.17MPa to 5.92MPa by using PVT autoclave, then the effects of temperature, pressure, base oil content and drilling fluid viscosity on the test target are analyzed by using multiple experimental data processing methods. It is found that the variation of ethane solubility with pressure and temperature are almost linearly under interested ranges, the effects of pressure (1.24 ~ 2.78%/MPa) are almost 50 times higher than that of temperature (-0.013 ~ -0.049%/℃) in oil-based drilling mud, the solubility of ethane decreases as viscosity increases, the ethane solubility in 80% and 90% of oil-based muds are about 1.6 times and 2.0 times higher than that in 70% of oil-based mud under the same test conditions. Models for predicting ethane solubility have been developed using screening procedures and statistics regression, which can be integrated into gas-liquid flow models so as to investigate flow behavior while gas kicking.