Lawrence Berkeley National Laboratory

The concept of injecting supercritical CO2 (sCO2) into a geothermal reservoir was computationally investigated to assess its performance in terms of the benefit of using CO2 captured from fossil power plants for geothermal heat mining. A coupled wellbore-reservoir system was simulated considering the flow of pure sCO2 in an injection well, the interaction of sCO2 and water in a permeable reservoir, and the flow of the two-phase mixture of sCO2 and water in a production well. Results of simulations indicate that this CO2 application is capable of providing a good source of renewable energy. It was found that for a reservoir with a 0.08 km3 volume, about 8-9 MWth could be extracted in a steady state fashion for a 30-year lifetime operation. This is approximately equivalent to 100 MWth/km3. A sensitivity analysis provided information on the impact of certain parameters on the performance of the integrated system. The injection flowrate, the distance between the production and injection wellbores and the penetrating depth of the production wellbore into the reservoir have a first order impact on the pressure management of the reservoir. Additionally, CO2 injection temperature has a large effect on the thermosiphon characteristics of the system.