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

Abstract

Using CO2 as a working fluid in enhanced geothermal systems may allow larger heat extraction for a given pressure gradient. We simulate an idealized initially low-salinity brine-filled reservoir. We inject CO2 and extract heat from the produced fluid that is at first brine and later CO2. As the aquifer dries out, salt precipitate in the reservoir inducing, after less than 5 years, clogging of the fractures next to the production well. To reduce this effect, we have also simulated combined brine and CO2 injection. This strategy more than doubles the life of the well at the expenses of a smaller rate of heat extraction, with a total heat extracted that is 40% larger than in the dry CO2 case. Simulation of more realistic geologic settings and other fracture plugging models would be necessary to evaluate the feasibility of CO2-EGS in any particular reservoir.