Experimental and pore-scale simulation study on CO2 diffusion in porous media saturated by brine and oil

Abstract

CO₂ diffusion in porous media saturated by brine and oil plays an important role in both enhanced oil recovery (EOR) and carbon capture, utilization and storage (CCUS). However, it is challenging to thoroughly investigate the diffusion of CO₂ in porous media with varied water saturations using numerous experiments. In this study, we develop a pore-scale numerical simulation method to predict CO₂ effective diffusion coefficient (D_eff) in cores with different water saturations. First, a new method for determining the CO₂ effective diffusion coefficient in cores with different water saturations is developed by coupling axial constant-volume diffusion (ACVD) experiments with mathematical models. Using this method, we determine D_eff in cores with water saturations ranging from 0 % to 100 %. In the numerical simulations, a model is developed to investigate CO₂ diffusion in porous media. Subsequently, history matching of the CO₂ diffusion amount in porous media is conducted to determine the D_eff in these media with different water saturations. We validate the accuracy of the pore-scale numerical model developed in this study by comparing the D_eff calculated using this model with those determined from experimental results. The pore-scale numerical simulations indicate that non-uniform CO₂ diffusion is prevalent in formations with various water saturations, as CO₂ preferentially diffuses into pore spaces occupied by oil. Finally, we develop a generalized D_eff prediction model using the Alternating Conditional Expectation (ACE) algorithm. This study may provide some new insights into CO₂ diffusion in porous media saturated by brine and oil.