Optimizing Gas Flooding with Fractal Theory for Water Coning Suppression and Oil Recovery Enhancement

This study addresses high water cut and low recovery in bottom-water sandstone reservoirs by optimizing CO2 and N2 foam flooding parameters. The key innovation is the pioneering application of fractal dimension to quantitatively characterize water coning morphology during composite gas flooding. A numerical simulation assessed composite gas type, injection gas ratio, sequence, speed, volume, and injection–production ratio. Fractal dimension quantified water coning. Optimal conditions were: 2:1 injection gas ratio (CO2 then N2 foam), 140 t/d injection speed, 0.31 PV volume, and 1:3.2 injection–production ratio. This achieved 39.52% recovery over 15 years—a 4.89% increase, adding 3.17 × 104 t of oil. Fractal dimension fell to 1.672. Sensitivity analysis showed the injection gas ratio most affects oil output. The injection volume best suppresses water coning. The injection speed has low sensitivity. Key interactions exist between volume, gas type, and injection–production ratio. Injection gas ratio, volume, and injection–production ratio are crucial for development control. The proposed methodology presents a viable strategy for enhancing oil recovery in similar reservoirs, with broader implications for advancing CO2 utilization and supporting carbon management objectives in the petroleum industry.