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Dissolved Gases and a Carbon Dioxide Balance from the San Vicente Geothermal Field in El Salvador, Central America

Grimaldi, David Andres
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1615276127141058

Abstract Details

2021, Master of Science (MS), Ohio University, Geological Sciences (Arts and Sciences).
Past geological, geochemical and geophysical studies by LaGeo have shown the presence of a 12 km2 geothermal reservoir at San Vicente Geothermal Field (SVGF) . This reservoir has an estimated thickness of 600 to 1200 m underneath a 600 to 800 m thick capping rock. All this located under the northern flank of San Vicente volcano. Potential drilling targets for geothermal exploitation are determined through visual geographical correlation of geological, geochemical and geophysical variables. However there are statistical methods such as geographical weighted regression and cluster analysis that allow us to establish statistical correlation between the geochemical and geophysical variables that are related to fluid storage and flow. Carbon dioxide (CO2) diffuse degassing and other gases, and geophysical variables such as resistivity and gravity, are related to high permeability areas, such as faults, and underground fluid movement within a geothermal field. In order to establish more accurate drilling targets for geothermal exploitation, a better and more objective data interpretation can be achieved by establishing the statistical correlation of CO2 diffuse degassing to other geochemical or geophysical variables. We have used Geographically Weighted Regression (GWR) models via computer program GWR4 to determine the statistical correlation between the space dependent geophysical and geochemical variables. Data from San Vicente Geothermal Field in El Salvador was used to determine the spatial correlations between CO2 soil concentration and the concentrations of He, 222Rn, 220Rn, Hg, resistivity and gravity measurements. Bivariate GWR showed statistically significant correlations between CO2 diffuse degassing, He concentration, Hg concentration, 222Rn concentration, 220Rn concentration and Magneto-telluric measurements. He concentration had the greatest statistical weight (𝑅𝑝 2 = 0.55, F = 7.21, p < 0.001). Stepwise multivariate GWR was applied and the most statistically significant multivariate regression model for CO2 soil concentration included He concentration, Hg concentration, 222Rn concentration, 220Rn concentration and Magneto-telluric measurements (𝑅𝑝 2 = 0.69, F = 6.79, p < 0.001). Geophysical and geochemical variables appear to be strongly correlated. This behavior is the result of the influence of the geological properties and fluid storage and movement on the released gases from the reservoir and the variations in the geophysical properties. Data integration demonstrated that this type of statistical analysis can provide an additional layer of robustness in the decision making process in the search for potential drilling targets. There is a potential groundwater recharge of 26.37% of the total precipitation in the area to the shallow aquifer. This shallow aquifer has low productivity and has low porosity. Most of the carbon dioxide flowing through the fissured deeper aquifer and the shallow aquifer is degassed from a deeper magmatic chamber. The atmospheric carbon dioxide dissolved in rainfall contribution to the system is negligible compared to the amount of carbon dioxide contributed by the magma chamber.
Dina Lopez, Dr (Advisor)
Katherine Fornash, Dr (Committee Member)
Schenk Xizhen, Dr (Committee Member)
230 p.
Earth; Energy; Environmental Geology; Geochemistry; Geographic Information Science; Geology; Natural Resource Management; Statistics
Geothermal; Geochemistry; Statistical Analysis; Geographical Weighted Regression; Mass Balance; Carbon Dioxide Balance; Geothermal Field; San Vicente; El Salvador

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Citations

  • Grimaldi, D. A. (2021). Dissolved Gases and a Carbon Dioxide Balance from the San Vicente Geothermal Field in El Salvador, Central America [Master's thesis, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1615276127141058

    APA Style (7th edition)

  • Grimaldi, David. Dissolved Gases and a Carbon Dioxide Balance from the San Vicente Geothermal Field in El Salvador, Central America. 2021. Ohio University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1615276127141058.

    MLA Style (8th edition)

  • Grimaldi, David. "Dissolved Gases and a Carbon Dioxide Balance from the San Vicente Geothermal Field in El Salvador, Central America." Master's thesis, Ohio University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1615276127141058

    Chicago Manual of Style (17th edition)

ohiou1615276127141058
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This open access ETD is published by Ohio University and OhioLINK.
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