A study was conducted to assess the feasibility of using supercritical carbon dioxide (sCO_2) injection for heat mining from geothermal reservoirs in Mexico. Mexico is aiming at expanding the role of geothermal energy, and renewable energy in general, in the country's power generation matrix. Four high-enthalpy sites are currently under commercial ownership and production by the Federal Commission of Electricity (CFE) in Mexico, totaling 958 MW_e. Traditional water-based geothermal systems require significant amounts of water, a high permeability and porous formation and sufficiently high subsurface temperatures. Supercritical CO_2 is recognized to have good mobility and flow properties that make it an excellent alternative to water for heat recovery from geothermal reservoirs, thus expanding the range of usable natural geothermal formations. CO_2 is expected to be available in the future from carbon capture systems added to fossil-fired power plants for greenhouse gases abatement. CO_2 as a geothermal heat mining fluid also provides the added benefit of carbon storage within the geothermal formation. Estimations of heat mining potential using sCO_2 were performed using the TOUGH_2 computer software. Simulations for three representative reservoirs in Mexico (Hard Dry Rock, HDR - Acoculco (260°C, 160 bar), Deep Saline Aquifer, DSA - Puruandiro (165°C, 100 bar), and Low Enthalpy Reservoir, LER - Agua Caliente Comondu (95°C, 75 bar) indicate that CO_2-based systems have better heat mining potential than H_20-based systems, corresponding to enhanced heat extraction rates as high as 160 percent with respect to the H_20-based systems, with the heat mining benefit by sCO_2 increasing in inverse proportion to the site subsurface temperature. Additional simulations for twenty-one characterized geothermal sites in Mexico estimate a total power generation potential with sCO_2 of 1,161 MW_e. This represents 51.4 percent additional power generation that can be mined by the use of sCO_2, in comparison to water. Additionally, a sCO_2-based geothermal system would be able to sequester in these twenty-one geothermal reservoirs, over an expected 30-year life of the reservoir, approximately 72 million tons of CO_2, or about 10 percent of the current total CO_2 emissions inventory for the country.
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