Mechanistic Characterization and Synergistic Optimization of Residual-Oil Distribution in Low-Permeability...

Residual-oil characterization and recovery in low-permeability reservoirs during ultrahigh-water-cut stages remain challenging due to strong heterogeneity and complex bottom-water interactions. However, quantitative understanding of the coupled effects of microstructures and sedimentary rhythm on residual-oil distribution in edge-bottom-water systems remains limited. In this study, the H307-X46 block was investigated using integrated geological modeling and dynamic numerical simulation. A high-fidelity three-dimensional reservoir model was constructed by integrating geological, petrophysical, and production data, and validated through 10-year historical matching with a Root Mean Square Error (RMSE) of less than 5% for cumulative oil production. Results indicate that residual-oil distribution is governed by the coupled effects of sedimentary rhythm and microstructures. Three dominant controlling factors were identified and ranked by Gray Relational Analysis: well-network perfection (relational grade 0.82), sedimentary heterogeneity (0.75), and microstructural features (0.68). Based on these controlling mechanisms, a mechanism-oriented optimization strategy was implemented, resulting in recovery-factor improvements of 1.38 and 1.23% for reperforation and infill drilling, respectively. This study establishes a quantitative workflow linking residual-oil controlling mechanisms with integrated optimization in low-permeability marginal reservoirs.