Techno-Economic Optimization of Hot-Water Flooding and Injection Conversion Strategies for a Heavy Oil Reservoir: A Case Study of the A66 Block

Heavy oil reservoirs typically suffer from low recovery efficiency and high development costs during thermal production. This study investigates the A66 heavy oil reservoir and proposes an integrated hot-water flooding and hot-to-cold injection strategy. Laboratory experiments, numerical simulations, and techno-economic analysis are combined to optimize injection temperature, conversion timing, and injection parameters. Results show that injection temperature strongly affects oil recovery. Increasing temperature from 40 °C to 60 °C significantly improves recovery by reducing oil viscosity and enhancing mobility. However, further increases to 80 °C and 100 °C provide only marginal additional improvement, indicating a clear diminishing return effect. Considering both recovery performance and energy consumption, 60 °C is identified as the optimal injection temperature. Simulation results indicate that the timing of hot-to-cold conversion has a limited impact on final recovery, while significantly affecting development cost. A conversion window at a water cut of 10–20% achieves a balanced performance between displacement efficiency and thermal cost reduction. In addition, unstable injection improves sweep efficiency by dynamically adjusting flow paths and enhancing both areal and vertical displacement. A coupled hot-to-cold injection strategy is therefore proposed. It integrates temperature optimization, injection mode design, and conversion timing to improve both recovery and economic performance. Compared with conventional constant-temperature flooding, the proposed strategy better accounts for the time-dependent evolution of reservoir thermal conditions and fluid properties. Techno-economic evaluation confirms that the optimized scheme achieves higher economic efficiency while maintaining stable recovery improvement, demonstrating strong potential for field application in similar heavy oil reservoirs.