Optimal Selection of Gas–Water Separation Agents and Experimental Characterization of Tapping Potential Water-Sealed Gas

Exploiting water-sealed gas in fully water-involved sandstone reservoirs is key to sustaining and increasing production for such gas reservoirs. Based on this, this study proposes a technology that combines formation energy replenishment with gas-water separation agent injection to disrupt gas-water interface equilibrium, thereby enabling water-sealed gas exploitation. Through static performance evaluation and microfluidic visualization experiments, high-efficiency gas-water separation agents were selected, and their mechanisms for tapping potential different types of water-sealed gases were characterized. Results show that selected agents exhibit universal applicability under experimental conditions, reducing the gas-water interfacial tension by ∼50% under reservoir conditions. Agent No. 10 achieves 63% reduction at 0.3 wt % concentration. The agents primarily exploit water-blocked gas (58.1%) and trapped gas (59.2%) in high-sweep-efficiency zones through: gas-water separation agents contacting the gas-water interface → gas-water interfacial tension progressively decreasing → internal forces exceeding external forces, inducing bubble expansion → bubble fragmentation and migration → bubble deformation and coalescence → bubble fragmentation and migration. For gases in low-sweep-efficiency zones, exploitation ratios are lower: edge water-blocked gas: 15.8%, blind-end residual gas: 2%, and edge band gas: 11.2%. This study provides crucial technical support for developing water-sealed gas in water-injected gas reservoirs.