Exogenous and Endogenous Displacements in 3D Porous Media

Gas displacement is ubiquitous in engineering applications and natural phenomena. Compared to exogenous displacement, studies on endogenous displacement within 3D porous media remain scarce. This study investigates gas invasion and gas exsolution by depressurizing CO 2 ‐saturated solution in specimens with distinct wettability. Gas‐brine distribution, bubble nucleation and growth processes were visualized via micro‐CT. The results show that endogenous displacement efficiency is almost always higher than that of exogenous displacement, by up to 63% in the same specimen. Hydrophobic sands provide more nucleation sites and stimulate bubble exsolution in the saturated solution, leading to the highest endogenous displacement efficiency. Pore‐scale observations show that each individual bubble must displace the brine in the pore before invading into an adjacent pore and once one cluster breaks through and reaches the outlet, it does not replace more water. Therefore, more nucleation sites are confirmed as the key to improving displacement efficiency or energy recovery.