Numerical study on thermal performance of enhanced geothermal system with CO2 using multistage hydraulic stimulation

A novel collaborative research project aimed at utilizing CO2 to create an artificial geothermal reservoir and extract heat by circulating CO2 was initiated in 2021. In this study, we demonstrated that CO2 may significantly enhance thermal power production in geothermal reservoirs over the long term without significant thermal breakdown. First, we compare our numerical results of production temperature with an analytical solution using a single fracture model to verify our results. Subsequently, we simulate thermal power production over a 40-year period under constant bottom hole pressure and mass flow rate conditions using a single fracture model to understand the thermal performance of water and CO2. Finally, we model an EGS reservoir created using a multistage stimulation strategy to evaluate the thermal power production at a field scale. By assuming an EGS reservoir comprising a set of horizontal injection and production wells as well as a reservoir temperature 200 °C, circulating CO2 is expected to output at least 8 MWth for 40 years. Additionally, CO2 yielded a higher thermal output than water in all the test cases. Through comprehensive numerical simulations, we demonstrate that a multistage stimulation strategy is one of the promising approaches for geothermal power generation utilizing CO2. Further studies are required to establish an optimal design, including the costs of the overall system for realistic social implementation of geothermal power generation utilizing CO2.