Simulation of CO2-EGS in a Fractured Reservoir with Salt Precipitation

AbstractThe use of CO2 as a working fluid in place of formation brines in Enhanced Geothermal Systems (EGS) could allow, in addition to CO2 sequestration, a more efficient recovery of reservoir heat for any given pressure gradient between injection and production wells. We simulate an idealized low-salinity brine-filled reservoir in which we inject CO2. We produce heat from the extracted fluid that is at first just brine, later brine + CO2, and finally CO2 only. As the CO2 plume develops the aquifer dries out, precipitating salt and inducing clogging of the fractures in proximity to the production well. To mitigate this effect, we have simulated combined brine and CO2 injection that, at specific mass fractions, doubles the life of the well but limits the rate of heat extraction. The total heat extracted over the life of the well is 40% larger than in the dry CO2 case. Simulation of more realistic geologic settings with involvement of chemical reactions would be necessary to evaluate the feasibility of CO2-EGS in any particular geothermal system