CARBONSAFE PHASE 2: EVALUATING THE CO2 STORAGE POTENTIAL OF DEEP JURASSIC AND PERMIAN SANDSTONE RESERVOIRS, EASTERN UINTA BASIN, UTAH

The Utah Geological Survey is evaluating the carbon dioxide (CO₂) storage potential of subsurface geologic reservoirs in the eastern Uinta Basin as part of a U.S. Department of Energy-funded CarbonSAFE Phase 2 project. The reservoirs under consideration include eolianites in the Jurassic Entrada and Nugget Sandstones and the Permian Weber Sandstone that are buried at depths of 9,500 feet and greater along the north side of the Douglas Creek Arch. Just two historical exploration wells penetrate these strata in the study area and provide limited petrographic and well log data. With these limitations, we applied a simple methodology to quantify rock properties using digitized geophysical logs and preserved rock material in the form of well cuttings and core chips from the target intervals. We conducted X-ray fluorescence (XRF) analysis of each well’s preserved rock material to refine the subsurface stratigraphy and identify the depth and thickness of potential reservoir and seal units. This led to our confirming the presence of the Nugget Sandstone in this area, which was initially in question and not specifically identified in the well logs. Thin sections were made from cuttings and core chips, impregnated with blue epoxy to highlight free pore space, and stained with alizarin red to identify the presence of calcite cement. These thin sections were used to determine composition, cementation, and porosity, key reservoir characteristics that influence CO2 storage. Photomicrographs were taken of the thin sections, uploaded into a digital point counting software, and analyzed for inherent rock properties. This program identifies blue pixels (epoxy filling pore space) from the image and calculates the percentage of pore space. The deeply buried (11,000+ ft) Weber Sandstone consists of tightly packed quartz grains with significant calcite and clay cement, with an average porosity of 0.74%. In the same well, core chips from the Entrada Sandstone averaged 6.77% porosity with multiple zones between 10% and 16%. Patchy calcite and clay cement were observed. Continued analysis of thin sections from hand samples collected in the field will help refine the range of possible porosities for each reservoir interval and determine whether differences in porosity may be due to depositional environments or diagenetic histories.