Numerical simulation of single-well enhanced geothermal power generation system based on discrete fracture model

Abstract

This study proposes a single-well enhanced geothermal system (SEGS) to mitigate the high-risk of traditional Enhanced Geothermal Systems (ESGs) with two or more wells and enhance the general applicability. A detailed thermodynamic model that couples the wellbore, reservoir, and organic Rankine cycle is built. For the reservoir, a three-dimensional flow and heat transfer model featuring a discrete fracture network is employed. The effects of injection flow rate, injection temperature, branch well length, and branch well spacing on net output work, pump power consumption, thermal efficiency, and exergy efficiency have been investigated. The results indicate that an increase in the injection flow rate improves the shaft power of the expander and the power consumption of the injection pump. An optimal flow rate of 30 kg/s is identified, which maximizes the annual net power output to 1221.2 kW. Additionally, an increase in the injection temperature is found to enhance the buoyancy effect, thereby improving both thermal and exergy efficiency, and reducing the power consumption of the injection pump. The maximum net output power is achieved at an injection temperature of 60 °C. The study also notes that the branch well length has a negligible effect on thermal and exergy efficiency and expander shaft work. However, a longer branch well length contributes to a decrease in the power consumption of the injection pump and an increase in the net power output. Finally, it is observed that increasing the lateral well spacing slows the rate decay of the production temperature. A spacing of 360 m is found to yield a maximum annual net output power of 1259.4 kW. In conclusion, this study offers significant insights and practical guidance for the development and utilization of SEGS, demonstrating its potential as an effective alternative to conventional EGS methodologies.