Summary

Advances in engineering techniques have re-stimulated interest in some of North America's great hydrocarbon producing basins. Whilst the basins have been extensively mapped, drilled and discussed, the success of future drilling campaigns lies in the detail of these complex systems. The Powder River Basin (PRB) contains a number of stacked plays, each varying in their capacity and complexity. Intra-play heterogeneities only serve to compound this complexity, with micron scale observations impacting regional scale completion programs.

The strata of the Early to Mid-Cretaceous of the PRB reflect the periodic high- and lowstand episodes of the Cretaceous Western Interior Seaway. During this time, varying volumes of water and sediment infiltrated the basin and admixed with the seaway resulting in a series of interbedded marine and terrestrial-dominated silts, muds and sands. Typically these sediments are well preserved as thick successions of stacked plays. The connectivity of these units has delivered the conventionally prosperous Frontier and Muddy sandstone reservoirs, fed by the adjacent Belle Fourche and Mowry shale source rocks.

As the primary source rock in the Mid-Cretaceous section of the PRB, the Mowry shale has recently been targeted as an unconventional reservoir unit. Supported by advancing technologies, a number of recent drilling campaigns targeting the Mowry have delivered significant encouragement for continued investment in the Mowry as a target formation.

Here, we analyze the evolution of the PRB during the Early to Mid-Cretaceous, focusing on the Mowry, and its representation in a variety of media accessible in the present day – outcrop, core, wireline log and seismic data. Through combining these observations and interpretations, we qualify and quantify key stratigraphic members within the Mowry, their distribution, and the residual impression syn- and post-depositional events have had on their constituents.

With this knowledge in place, we grade areas of greatest prospectivity across the basin and support this ranking with evidence from the various datasets.

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