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Basinward Trends in Fluvial Architecture, Connectivity, and Reservoir Characterization of the Trail Member, Ericson Sandstone, Mesaverde Group in Wyoming, Utah, and Colorado, U.S.A.

Abstract

The Late Cretaceous Trail Member of the Ericson Sandstone represents a regionally extensive fluvial system that transported sediments from the Sevier fold and thrust belt to the Western Interior Seaway. The Trail Member is exposed along hundreds of square kilometers in Wyoming, Utah, and Colorado due to post-depositional Laramide uplift structures. Additionally, the Trail Member is a petroleum reservoir target that has unpredictable production rates due to the unknown behavior and connectivity of channel sandstones. The abundant outcrop, well and core data available allows for a comprehensive analysis of how the fluvial architecture, connectivity, and reservoir characteristics change along 75 kilometers of depositional dip. Detailed stratigraphic columns from three locations from Clay Basin along the Utah/Wyoming border moving more basinward into Northwestern Colorado allow for the analysis of facies distribution, hand sample collection for reservoir characterization, and scintillometer data collection to tie outcrops to the subsurface. Additionally, photogrammetric analysis of the three locations allow for the identification of broad trends throughout the strata. Core and thin sections from producing fields just north of the NW Colorado sections also allow for small scale analysis of types of porosity, the distribution of grain size and type, and how subsurface facies distribution differ to outcrops. Moving basinward, Trail strata show little variability in the thickness and net-to-gross, contrary to what might be expected. However, important changes are observed at the basinward outcrops in NW Colorado. Though lenticular, fluvial-dominated sands are still common, preserved woody material, mud cracks, and burrows are observed only in this area. Channels appear to be less erosive, and the width-to-depth ratio increases in this distal setting as well. This suggests periodic deltaic processes were at work here, showing that we are close to the margin of the Cretaceous Interior Seaway. This helps to constrain the spatial extent of the system, confirming that it has prograded far into the basin and is a much longer distributary system than what is typically seen in the Sevier foreland basin during the Cretaceous. This suggests that reservoir character as described at the outcrop is applicable to nearby exploration and development targets, and outcrops along the margin of the basin are valid analogs for the subsurface system.