Experiments and modeling of CO2 solubility in water-based and oil-based drilling fluids

An experimental apparatus has been developed to measure the CO2 solubility in water, brines, polymer solutions, white oil and drilling fluids using the sample analysis method. The experimental results show that the electrolytes can significantly reduce the solubility of CO2 in water and the salting-out effect can be enhanced by increasing the molar concentration of salt ions. The influences of different polymers are similar, which can reduce the gas solubility to a certain extent. Furthermore, CO2 solubility in the oil-based drilling fluid is significantly larger than that in the water-based drilling fluid. Considering the complicated interactions between gas, electrolytes, polymers and base oil in the drilling fluid, a simple and reliable model for predicting the CO2 solubility is developed. Validation of the model calculations against the experimental measurements indicates that the simulation errors of CO2 solubility in the water-based and oil-based drilling fluids are 3.47% and 6.75%, respectively.