A modified methodology to substitute U-shape well using a single well with fracture network: Design and performance

The increasing demand for low-carbon energy has led to the exploration of renewable energy sources, including geothermal energy. One potential method for accessing this energy is through the retrofitting of abandoned oil wells into geothermal wells. While there have been some previous efforts in this area, many of these methods suffer from low efficiency or high cost. In this study, we have proposed a novel retrofitting pattern for a single well embedded with an enhanced fracture system (EFS). Using COMSOL Multiphysics, a numerical model was established to investigate the effects of different reservoir and fracture properties on the performance of EFS. Our analysis showed that it is possible to replace a U-shaped well with a single well using EFS, and that the thermal power was more than four times greater than that of conventional borehole heat exchangers over a 50-year heat extraction period. We found that fracture permeability and aperture were the two most critical parameters for achieving high heat extraction performance in EFS. EFS exhibits significantly better performance compared to the traditional open-loop geothermal system (OLGS). Based on our findings, we recommend controlling the flow rate within the range of 10-20 kg/s and pumping proppant for optimal EFS design.