Wettability effects on supercritical CO2-brine immiscible displacement during drainage: Pore-scale observation and 3D simulation

Wettability is an important factor controlling the displacement of immiscible fluids in porous media and therefore affects the flow and transport of supercritical (sc) CO2 in geologic carbon sequestration. Because few studies have focused on the wettability effect in scCO2-brine flow systems, we experimentally and numerically tested influences of wettability on drainage at the pore network scale. Using a high-pressure micromodel-microscopy system, we performed experiments of scCO2 invasion into brine-saturated water-wet and intermediate-wet micromodels, and recorded the scCO2 invasion morphology under reservoir relevant conditions. We also performed pore-scale numerical simulations to infer 3D details of fluid-fluid displacement processes. During drainage under intermediate-wet conditions, we found higher scCO2 saturation, wider scCO2 fingering, and more compact displacement patterns. The simulation results are qualitatively consistent with the experiments. Through quantitative analyses of the experiments, we found that the reduced wettability decreases the displacement front velocity, promotes non-wetting phase pore-filling events in the longitudinal direction, delays the breakthrough time of invading fluid, and increases the displacement efficiency. Simulated results also show that the fluid-fluid interface area follows a unified power-law relation with scCO2 saturation, and show smaller interface area in intermediate-wet case which suppresses the mass transfer between the phases. These pore-scale results provide insights for the wettability effects on CO2-brine immiscible displacement in geologic carbon sequestration.