Numerical Simulation Study on Sequential Oil Production and Geothermal Conversion in Northern Songliao Basin

Under the global low-carbon energy transition, repurposing inefficient oil wells into geothermal wells for utilizing residual reservoir heat has become a critical strategy for sustainable oilfield development. This study focuses on the T Block of Toutai Oilfield. A three-dimensional (3D) geological model and a thermo-hydro-mechanical (THM) coupled numerical model were constructed using the CMG-STARS platform to explore the technical feasibility of converting inefficient wells into geothermal wells. The research quantitatively characterizes the influence of different production parameters on geothermal energy extraction efficiency, providing optimization strategies for the co-development of “oil-geothermal co-production” to achieve dual benefits of resource utilization and geothermal exploitation. Key findings include: (1) After sidetracking a horizontal well with a 342-m lateral section followed by fracturing and commissioning, the cumulative oil production reached 1,607 m3 in the first year. When daily oil production declined below the economic threshold of 1.3 t/d after four years, the well became suitable for geothermal conversion. (2) Under an injection rate of 300 m3/d and temperature of 20 °C, the average produced fluid temperature was maintained at 35.5 °C during the first year, with a 5% decline observed over 10 years. (3) At a fixed injection rate, higher injection temperatures resulted in smaller temperature differentials between produced and injected fluids. Specifically, at 300 m3/d, the heat extraction capacity with 5 °C injection temperature was 16% higher than that at 20 °C. (4) While increased injection rates enhanced heat production rates, they concurrently reduced produced fluid temperatures. Considering both thermal demand and economic viability, the optimal parameters were determined to be an injection temperature of 15 °C with a rate of 480 m3/d. These findings demonstrate the technical-economic feasibility of well repurposing for geothermal co-production. Parameter optimization not only enhances heat extraction performance but also extends system longevity, providing significant implications for facilitating oilfield green transition and advancing clean energy utilization.