Mechanisms of Enhanced Oil Recovery and Reservoir Adaptability of Hot Water-Chemical Composite Flooding

For offshore ordinary heavy oil reservoirs developed by conventional water flooding, challenges such as significant mobility differences between oil and water, rapid water cut rise, and low recovery rates persist. To address these issues, this study explores the utilization of platform waste heat and geothermal energy to implement low-cost hot water-chemical composite flooding for enhanced oil recovery (EOR). The primary objective is to clarify the oil enhancement mechanisms and reservoir adaptability of this technology. Through one-dimensional and two-dimensional physical simulation experiments, the mechanisms and incremental oil recovery effects of hot water combined with different gases and chemical agents were investigated, and the optimal injection medium combination for hot water-chemical composite flooding was identified. Numerical simulation methods were employed to establish technical thresholds for reservoir screening in hot water-chemical composite flooding. Physical simulation results revealed that carbon dioxide exhibited the best performance among gases in improving displacement efficiency, while chemical agents further enhanced displacement efficiency by 2.7% compared to CO₂. In terms of sweep volume expansion, the energy-enhancing and production-assisting effects of gases, as well as the plugging and profile control effects of chemical agents, both contributed to expanding the sweep range of hot water. Notably, the latter increased sweep volume by 15% compared to the former. Using the optimal injection medium combination, hot water-chemical composite flooding achieved an 11.6% higher recovery rate than conventional hot water flooding. Numerical simulation results indicated that the key geological factors influencing the effectiveness of hot water-chemical composite flooding, ranked by impact, were crude oil viscosity, reservoir permeability, and permeability contrast. Integrating technical effectiveness and economic feasibility, technical thresholds were established, incorporating geological parameters and inter-well flow characteristics. Based on these findings, target oilfields for hot water-chemical composite flooding implementation were identified, guiding the design of development plans and yielding favorable production outcomes. This research provides a novel direction and technical support for low-carbon, efficient development of similar reservoirs, demonstrating significant practical value.