Horizontal well-assisted depressurization method for geothermal exploitation from fractured granite reservoir at Yangbajing geothermal field

Utilizing the geological information obtained from the ZK4001 borehole of Yangbajing geothermal field, a horizontal well system with depressurization method was proposed to achieve heat production from fractured granite reservoir. Numerical simulations under the assumed geological and operational conditions were conducted to investigate the geothermal exploitation performance, the power generation potential and its dependent factors. Assessment indicates that within a reservoir spanning depths of 950-1350 m and maintaining an average temperature of 248 °C, at a production pressure of 2.5 MPa, the production temperature remains stable at 230 °C with a steam saturation of 0.28 for 12.5 years, subsequently experiencing a decline. Over a lifespan of 20.6 years, the fundamental horizontal well system achieves an electric power of 32.28-23.12 MW, exhibits a reservoir impedance of 0.072-0.096 MPa/(kg/s), requires a pump power of 1.14-1.83 MW, and demonstrates an energy efficiency of 28.87-12.65, suggesting favorable geothermal exploitation performance under the modeled conditions. The estimated reduction in greenhouse gas emissions amounts to 1.63-5.63 Mt. Sensitivity analysis indicates that, for the geothermal exploitation by the depressurization method, the production pressure has a significant impact on geothermal exploitation performance. Enhancing the permeability of the reservoir can effectively decrease flow impedance, minimize internal energy consumption, and result in improved energy efficiency. Moreover, adjusting the injection flow rate within a specific range can enhance the system's energy efficiency.