The Basin and Range provides excellent opportunities for geothermal resource development. In addition to large fault-controlled geothermal exploration targets along basin margins, elevated heat flow and presence of porous and permeable sedimentary rocks within the sedimentary basins are candidates for sedimentary geothermal energy production. Using a sedimentary approach has the potential to dramatically expand geothermal production in both established and frontier basins. This study characterizes Mesozoic siliciclastic reservoirs through detailed outcrop characterization and laboratory analysis of reservoir quality to assess suitability for sedimentary geothermal exploration.

Based on porosity and permeability measurements from 164 samples and thin sections from key stratigraphic intervals, three siliciclastic units were identified as prospective reservoir targets. These units have median porosities of 15.7% (Springdale Member of the Kayenta Formation), 15.1% (Moenave Formation), and 11.4% (Shurtz Tongue of the Navajo Sandstone), with median permeabilities of 18.7, 10.2, and 6.4 md, respectively. Regression analysis of porosity/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. Porosity and permeability variability within each unit is substantial, and the Navajo Sandstone in particular ranges from submillidarcy to 379 md across three sampled localities. Petrographic description demonstrates that this high variability of porosity and permeability is caused by heterogeneity in textural and compositional maturity, diagenetic alteration, and cementation. This highlights the need for detailed petrographic characterization of potential sedimentary geothermal reservoirs to understand lithological factors impacting spatial distribution of porosity and permeability.