Abstract

The transition zone between the Colorado Plateau and Basin and Range provinces of southwestern Utah provides excellent opportunities for future geothermal resource development. A combination of large fault-controlled extensional basins with outcrop analogs along basin margins, an elevated heat flow and thermal regime and the presence of porous and permeable sedimentary formations within extensional sedimentary basins allow for sedimentary geothermal exploration and development. Utilizing a reservoir-centered approach has the potential to dramatically expand the economic limits of geothermal plays in both established and frontier basins. This study characterizes a sedimentary geothermal system in Iron County Utah, centered on the Escalante Basin, through detailed reservoir characterization of Mesozoic siliciclastic reservoirs and basin modeling of subsurface strata to determine thermal suitability of prospective reservoirs. Based on porosity and permeability measurement of 89 outcrop samples and thin-section investigation of key intervals and facies, the study identifies three units of Mesozoic siliciclastic strata as prospective reservoir targets in the primary sample location in Cedar Canyon, just east of Cedar City, UT. These units have median porosities of 15.7% (Springdale Sandstone Member of the Kayenta Formation), 15.1% (Upper Dinosaur Canyon Member of the Moenave Fm), and 11.4% (Navajo Sandstone), with median permeabilities of 18.7 mD, 10.2 mD, and 6.4 mD, respectively. At other sample locations near Parowan and Kanarraville, UT we identified significant reservoir potential in the Main Body of the Navajo Sandstone with median porosity and permeability ranging from 15.6% to 21.4% and 19.5 to 237 mD, respectively. Regression analysis of porosity and permeability data from outcrops shows a strong correlation, suggesting that permeability values can be predicted using log or core-based porosity values from nearby geothermal and oil wells. Spatial and stratigraphic variability within each unit is substantial, however -- the Navajo Sandstone in particular ranges from 1 to 379 mD across three sampled localities, and the Springdale Sandstone Member exhibits permeability ranging from 9.2 to 129.0 mD in a 25 m interval. Petrographic description of reservoir units demonstrates that this high variability of porosity and permeability is due to heterogeneity in textural and compositional maturity, diagenetic alteration, and cementation and is related to lithofacies and environments of deposition. This highlights the need for detailed petrographic characterization of potential sedimentary geothermal reservoirs to understand lithological factors impacting spatial distribution of porosity and permeability. In the study area and stratigraphic interval of interest, the study identifies prospective flow units within the Moenave Formation, Kayenta Formation, and Navajo Sandstone. Basin modeling indicates that these reservoirs lie within a sufficiently high-temperature window (125-200°C) along a structural trend from Table Butte to Newcastle, suggesting the potential for stacked geothermal resource development across multiple reservoirs. Basin modeling also suggest that porosity and permeability are preserved at these depths. The methods and findings presented in this paper provide a foundation for future reservoir characterization and subsurface modeling workflows for basin-centered geothermal projects in the Basin and Range. These approaches can help identify and characterize prospective reservoir units from proximal outcrop analogs, improving the efficiency of geothermal exploration and development in this region.

Degree

MS

College and Department

Computational, Mathematical, and Physical Sciences; Geological Sciences

Rights

https://lib.byu.edu/about/copyright/

Date Submitted

2025-04-15

Document Type

Thesis

Handle

http://hdl.lib.byu.edu/1877/etd13573

Keywords

sedimentary geothermal, Navajo Sandstone, reservoir characterization, basin modeling, porosity-permeability, Basin and Range

Language

english

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