Sedimentological controls on reservoir heterogeneity in the eolian Entrada Sandstone: implications for geologic carbon storage

ABSTRACT Eolian successions are promising targets for geologic carbon storage, often comprising thick, laterally extensive sandstone bodies with high porosity and permeability. However, their effective use as subsurface reservoirs requires a thorough understanding of their stratigraphic complexity and the controls it exerts on reservoir heterogeneity. This study presents a detailed evaluation of the sedimentology, stratigraphy, and reservoir character of the wet eolian Jurassic Entrada Sandstone. Seven stratigraphic sections were measured and correlated in the vicinity of Dinosaur National Monument in northeastern Utah, USA, including 6 sections across a 3.4 km transect. A drone-based photogrammetric model near the seventh section enabled high-resolution visualization and quantification of architectural elements over a horizontal distance of roughly 160 meters. Although the study area does not encompass the full spatial extent of a typical CO2 storage reservoir, the stratigraphic relationships documented here provide insight into how wet eolian heterogeneity may influence subsurface flow. Four sandstone architectural elements were identified: large compound dunes (4–13 m thick), small compound dunes (0.6–4 m), simple dunes (0.3–1.4 m), and damp sand flats (0.2–5.5 m). These elements are organized into alternating dune and interdune–flat packages that are laterally continuous, vary in thickness, and show more complex facies distributions than previously recognized. Porosity and permeability data were collected for each element using thin sections, minipermeametry, and core-plug analyses. Despite significant variability according to methodology, porosity and permeability values suggest higher values for dunes compared to damp sand-flat deposits. Should these trends hold across scales, dune elements may represent primary flow pathways, while interdune sand flats are likely to serve as baffles to flow, resulting in a horizontally layered reservoir architecture with restricted vertical connectivity. Reservoir layering is further enhanced by lower-permeability bounding surfaces in cross-bed sets and grain-size variability at the bed and lamina scale. These sources of heterogeneity may promote reservoir compartmentalization and have important implications for subsurface modeling in wet eolian systems. This study highlights the sedimentological controls on reservoir heterogeneity in the Entrada Sandstone and provides an analogue for evaluating eolian reservoirs for carbon storage applications.