Combining geothermal energy capture with geologic carbon dioxide sequestration

Geothermal energy offers clean, renewable, reliable electric power with no need for grid-scale energy storage, yet its use has been constrained to the few locations worldwide with naturally high geothermal heat resources and groundwater availability. We present a novel approach with the potential to permit expansion of geothermal energy utilization: heat extraction from naturally porous, permeable formations with CO(2) as the injected subsurface working fluid. Fluid-mechanical simulations reveal that the significantly higher mobility of CO(2), compared to water, at the temperature/pressure conditions of interest makes CO(2) an attractive heat exchange fluid. We show numerically that, compared to conventional water-based and engineered geothermal systems, the proposed approach provides up to factors of 2.9 and 5.0, respectively, higher geothermal heat energy extraction rates. Consequently, more regions worldwide could be economically used for geothermal electricity production. Furthermore, as the injected CO(2) is eventually geologically sequestered, such power plants would have negative carbon footprints. Citation: Randolph, J. B., and M. O. Saar (2011), Combining geothermal energy capture with geologic carbon dioxide sequestration, Geophys. Res. Lett., 38, L10401, doi:10.1029/2011GL047265.