173-9 SEDIMENTATION AND SUBSURFACE CHARACTERIZATION OF THE LOWER CRETACEOUS MUDDY SANDSTONE AND THE UPPER CRETACEOUS SHELL CREEK & MOWRY SHALES, POWDER RIVER BASIN, WYOMING

Session: Geologic Energy Resources and Storage for Now and the Future

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Abstract:

Foreland basins comprise some of the most prolific hydrocarbon producing reservoirs and source rocks in the North American Rocky Mountain region. One of these major producing basins is the Powder River Basin (PRB). Located in northeastern Wyoming and extending into southeastern Montana, the PRB is one of Wyoming’s largest and most active hydrocarbon producing basins. The basin comprises various Mesozoic and Paleozoic strata with productive conventional and unconventional plays. Various studies have been done on both Mesozoic and Paleozoic stratigraphy within the basin. Historically, Cretaceous stratigraphy has been well studied and documented within the basin. However, continual industry innovations in the collection and processing of subsurface geological data are making possible more refined understanding of Cretaceous stratigraphy in the basin.

This study focuses on the upper Lower Cretaceous Muddy Sandstone Formation and lower Upper Cretaceous Mowry Shale intervals at basin scale, and the implications for tectonic and eustatic evolution prior to the development of the PRB. There is a general agreement that the Mowry can be divided into upper, middle, and lower sections. The middle section has been found to contain the highest TOC percentages based on prior work done with geochemical analysis. This study will update these findings with newly collected digital well data and produce higher-density regional basin coverage with type wells, while also utilizing petrophysical calculation methods to determine TOC percentages.

The Muddy being an older conventional reservoir and the Mowry a more recent unconventional play, the collection and utilization of digitized well log data from Enverus Prism with Petrel Software, in conjunction with analysis of in-house core, provides an effective approach for producing refined structure, isochore, net sand, and TOC maps for the basin. This information can then be used in generating interpretations of sedimentation history, basin infilling, and TOC distribution. In addition, published type wells with correlated Paleozoic stratigraphy from the USGS are used to generate PRB subsidence curves for multiple well locations across the basin. To further enhance sedimentation interpretations, U-Pb detrital zircon analysis is conducted on Muddy sandstone facies collected from core. This data will be compared with published detrital zircon and subsidence work done in both the western neighboring Big Horn Basin as well as the eastern neighboring Black Hills and their equivalent Muddy Formation intervals.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9324

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