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Building a Predictive Model for Stratigraphic Transitions and Lateral Facies Changes in the Cretaceous Almond Formation, Wyoming

Abstract

Building a Predictive Model for Stratigraphic Transitions and Lateral Facies Changes in the Cretaceous Almond Formation, Wyoming

The Cretaceous Almond Formation, located in the Greater Green River Basin, records deposition of coastal plain fluvial sandstones and shallow marginal-marine sandstones in a net-transgressive sequence along the western margin of the Cretaceous Interior Seaway (CIS) in the early Maestrichtian. The Almond Formation is an important hydrocarbon reservoir, with development along the Wamsutter arch and the margins of the Washakie basin. Further development of the Almond petroleum system away from current production requires extending our understanding of lateral facies changes and sequence stratigraphic architecture away from areas that have been previously studied. The aim of this research is to build a predictive model of the facies transitions and reservoir character along the Cherokee arch, along the southern margin of the Washakie Basin. Almond strata are exposed at either end of this structural feature, which is oriented roughly perpendicular to the shoreline of the CIS, along the margin of the Rock Springs Uplift and along the flank of the Rawlins uplift to the east. Initial examination shows that the lower Almond strata transition from fluviodeltaics in the west to shoreface strata in the east, while the upper Almond strata shows marine influence consistently across the ~125 km separating the two outcrop localities. The preservation of shoreface strata and related near-shore fluviodeltaics across large distances in the dip direction shows the large magnitude of the transgression with which it is associated, suggests that the system gradient was likely very gentle leading to wide facies belts, and that reservoir continuity could be favorable over significant distances. Further work to characterize the outcrops and integrate well data along the Cherokee Arch will add to initial outcrop observations and provide further detail to our understanding of this shoreface system, leading to better exploration decisions within the basin as well as a better understanding of transgressive systems along passive margins elsewhere in the geologic record.