--> Reservoir Architecture and Economic Implications of the Trail Member Fluvial Sandstones, Ericson Sandstone, Mesaverde Group

AAPG ACE 2018

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Reservoir Architecture and Economic Implications of the Trail Member Fluvial Sandstones, Ericson Sandstone, Mesaverde Group

Abstract

The Trail Member of the Cretaceous Ericson Sandstone, exposed near Dry Canyon on the southeast flank of the Rock Springs Uplift, represents a low-accommodation fluvial system, with a high net-to-gross relative to both underlying and overlying strata. It is dominated by trough-cross stratified sandstone with frequent, but often discontinuous, mud and silt interlayers. Individual beds are laterally discontinuous and pinch out regularly, but both lateral and vertical amalgamation of sandy fluvial channel elements is common. Though this strata is overwhelmingly sand-rich in the study area, measured sections and photogrammetric modeling of this fluvial system show both spatial and temporal variations in the character and connectivity of these sands that have important implications in this and analogous systems in the subsurface. The studied outcrops are only 15 miles from the Trail Unit, which produces from this and other intervals of Cretaceous strata, and the high resolution variability seen in outcrops can better inform models of the subsurface in this and other fields.

Near the top of the Trail Member in the field area, sands are more laterally accreting and less vertically stacked, suggesting that accommodation was lowest at this time, leading to frequent avulsion and lateral migration of channels. In contrast, the majority of the stratigraphic section is composed of multi-story channel complexes sands that are vertically thick but generally less laterally extensive. Both of these configurations have very different reservoir implications, and ongoing work shows that these trends extend more regionally throughout the Rock Springs Uplift. In addition, within the exposed potential reservoir sands of the field area, key facies identified in outcrop show variability in both porosity and permeability. Through both large-scale observation of architectural elements and much finer-scale investigation of rock properties and facies relationships, it is shown that effective reservoir connectivity and drainage patterns can be much more complex than anticipated, even in a sandy high net-to-gross systems such as this.