Evaluation of CO2-Fluid-Rock Interaction in Enhanced Geothermal Systems: Field-Scale Geochemical Simulations. (18th October 2017)

• Record Type: Journal Article
• Authors: Pan, Feng; McPherson, Brian J.; Kaszuba, John
• Other Names: Xu Tianfu Academic Editor.
• Is Part Of: Geofluids. Volume 2017(2017)
• Publication Date: 2017-10-18
• Subjects: Hydrogeology -- Periodicals; Sedimentary basins -- Periodicals; Fluids -- Migration -- Periodicals; Groundwater flow -- Periodicals; Geothermal resources -- Periodicals; Fluid dynamics -- Periodicals; Earth -- Crust -- Periodicals; 551.49
• DOI: 10.1155/2017/5675370
• Languages: English
• ISSNs: 1468-8115

Abstract

Abstract : Recent studies suggest that using supercritical CO2 (scCO2 ) instead of water as a heat transmission fluid in Enhanced Geothermal Systems (EGS) may improve energy extraction. While CO2 -fluid-rock interactions at "typical" temperatures and pressures of subsurface reservoirs are fairly well known, such understanding for the elevated conditions of EGS is relatively unresolved. Geochemical impacts of CO2 as a working fluid ("CO2 -EGS") compared to those for water as a working fluid (H2 O-EGS) are needed. The primary objectives of this study are (1) constraining geochemical processes associated with CO2 -fluid-rock interactions under the high pressures and temperatures of a typical CO2 -EGS site and (2) comparing geochemical impacts of CO2 -EGS to geochemical impacts of H2 O-EGS. The St. John's Dome CO2 -EGS research site in Arizona was adopted as a case study. A 3D model of the site was developed. Net heat extraction and mass flow production rates for CO2 -EGS were larger compared to H2 O-EGS, suggesting that using scCO2 as a working fluid may enhance EGS heat extraction. More aqueous CO2 accumulates within upper- and lower-lying layers than in the injection/production layers, reducing pH values and leading to increased dissolution and precipitation of minerals in those upper and lower layers. Dissolution of oligoclase for water as a working fluid shows smaller magnitude in rates and different distributions in profile than those for scCO2 as a working fluid. It indicates that geochemical processes of scCO2 -rock interaction have significant effects on mineral dissolution and precipitation in magnitudes and distributions.