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Geothermal energy is being explored as a supplement to traditional fossil fuel resources to meet growing energy demand and reduce carbon emissions. Geothermal energy plants harvest heat stored in the Earth’s subsurface by bringing high temperature fluids to the surface and generating steam to produce electricity. Development of geothermal resources is often inhibited by large upfront risk and expense. Successful mitigation of those costs and risks begins with efficient characterization of the resource before development. A typically successful geothermal reservoir consists of a fractured reservoir that conducts hydrothermal fluids and a cap rock seal to limit convective heat loss through fluid leakage. The controls on the system include the density and orientation of fractures, mechanical rock properties, and the local stress field acting on those rocks. The research presented in this dissertation utilizes diverse data sets to characterize core, wireline borehole logs, and laboratory data to describe the distribution of fractures, rock properties, and the orientation and magnitude of stresses acting on the borehole. The research demonstrates there is a potential resource in the region and describes the controls on the vertical extent of the hydrothermal fluids. The distribution of fractures is controlled by the distribution of elastic rock properties and rock strength. A cap rock seal is present that limits hydrothermal fluid loss from a fractured artesian reservoir at 1,745 m (5,726 ft). In addition to characterization of the resource, this research demonstrates that an equivalent characterization can be used in future exploration wells without the expense and risk of collecting core. It also demonstrates that multiple methods of analysis can be utilized simultaneously when some data are not available. Data collection from deep wellbores involves risk and data loss or tool failure is a possibility. In these cases, our methods show that successful characterization is still possible, saving time and money, and minimizing the financial risk of exploration

The Mountain Home (MH) geothermal system of the western Snake River Plain (SRP) magmatic province was discovered in 2012 by the Snake River Geothermal Drilling Project. Artesian flowing water with a temperature of 150°C was encountered at a depth of 1745 m below ground surface (mbgs) and extensive mineralized fracture networks of pectolite-prehnite, calcite, and laumontite were discovered in the recovered core. The objectives of this study are to: 1) describe the thermal and compositional history of past geothermal fluids, and 2) compare these fluids to modern fluids in order to characterize the evolution of the MH geothermal system and the geothermal potential of the western SRP. Core observations, thin section petrography, X-ray diffraction, and Electron Microprobe analyses were performed in order to describe mineral parageneses of various alteration zones. Carbon and oxygen stable isotope ratios along with temperatures of homogenization from fluid inclusions in hydrothermally precipitated calcite were measured along ~100 m of basalt core from 1709-1809 mbgs. The d13CPDB values in calcite range from -7.2 to -0.43 ‰ and d18OPDB values range between -20.5 and -15.9 ‰. An anomalous zone from 1722-1725 m depth displays a range in d13CPDB and d18OPDB of -1.9 to +0.88 ‰ and -17.1 to -8.1 ‰, respectively, suggesting non-equilibrium fractionation due to boiling. Carbon isotopic ratios suggest a mixture of deep-seated mantle derived and meteoric fluids. Fluid inclusion microthermometry has identified primary inclusions with trapping temperatures ranging from 168-368°C. A calcite-water geothermometer used to calculate paleo-fluid oxygen isotopic composition (-0.43 to +7.2 ‰ SMOW) and a comparison with present-day fluid oxygen isotopic composition (-3.2 ‰ SMOW) reveals a cooling trend with potential mixing of meteoric waters and deeply derived fluid. The MH geothermal system has cooled over time and reflects potentially less, if any magmatic fluid input presently into the system as there was in the past.

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1995 map of East Tennessee State University's VA Campus. Created 5/30/1995 by Johnson City GIS. Buildings can be identified using the building index on the left side of map. Parking info and the parking lot legend can be found on the bottom half. Some buildings are shaded using a colored pencil at an indeterminate time post publication. Physical copy resides with Johnson City, Geographic Information Systems Division. No scale is included. / https://dc.etsu.edu/rare-maps/1051/thumbnail.jpg

2005 map of East Tennessee State University's VA Campus. Created 12/9/2005 by Johnson City GIS. Buildings can be identified using the building index on the left side of map. Different types of buildings are denoted using a color scheme. Parking info and the parking lot legend can be found in the top left quadrant. Hydrants and related items are also included. The map is dated by a handwritten date in black ink in the bottom left corner. Physical copy resides with Johnson City, Geographic Information Systems Division. No scale is included. / https://dc.etsu.edu/rare-maps/1052/thumbnail.jpg

2013 map of East Tennessee State University's VA Campus. Created 12/4/2013 by Johnson City GIS. Buildings can be identified using the building index on the left side of map. Parking info and the parking lot legend can be found on the bottom right corner. Fire suppression system info is also included. Physical copy resides with Johnson City, Geographic Information Systems Division. No scale is included. / https://dc.etsu.edu/rare-maps/1053/thumbnail.jpg