Regional Fluvial Architecture and Reservoir Modeling of the Trail Member of the Ericson Sandstone, Mesaverde Group in Wyoming, Utah, and Colorado

Abstract

The Trail Member of the Cretaceous Ericson Sandstone is exposed along hundreds of square kilometers through Wyoming, Utah and Colorado along the flanks of several Laramide structural uplifts. This presents a unique opportunity to study the detailed architecture and better assess the reservoir potential of these strata in outcrop exposure, and relate these observations to producing fields nearby. The fluvial-dominated Trail Member formed as sediments traveled from the active Sevier thrust belt to the Cretaceous interior seaway, forming a basinward progradational clastic wedge along a relatively high gradient. Though there is an abundance of sand-rich strata in the Trail Member, production from this interval has been unpredictable in current and past fields such as the Trail Unit of SW Wyoming. Well-exposed outcrops allow for collection of many detailed stratigraphic columns that show facies heterogeneity, allow for collection of samples for reservoir characterization and scintillometer data acquisition along sections for correlation with nearby subsurface data. In addition to outcrop observations, photogrammetric analysis will provide high-resolution imagery to determine broad trends and fluvial architectural patterns to be used for static reservoir modeling.

Regional observations thus far suggest that spatial variability in the net-to-gross of the Trail Member, as well as temporal variability in the amount and character of reservoir sands, play an important role in the unpredictability of this reservoir. In the direction of depositional strike along the flanks of the Rock Springs Uplift, significant thickness variations can be seen in the Trail Member, as well as different relationships with the underlying Rock Springs Formation. Moving basinwards, the nature and stacking patterns of Trail sands change across more than 200 kilometers from the Clay Basin of Utah into Colorado. It is significant that although the character of the Trail strata changes appreciably along both strike and dip, this interval is consistently very rich in sand, and grain size does not change drastically along the length of observed outcrops. As part of this regional study, fine and broad observations from multiple localities will show the details of sediment delivery patterns and identify potential sediment fairways. This will lead to better predictability in exploration efforts, as well as a better understanding of both the fine-scale and regional paleogeography of the region.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018