New Study of the Upper Cretaceous Stratigraphy of the Powder River Basin

The Powder River Basin contains some of Wyoming’s most prolific oil and gas reservoirs as well as significant petroleum-generating source rocks. A new study from the Wyoming State Geological Survey (WSGS) aims to better understand the Upper Cretaceous stratigraphy of the basin’s unconventional tight oil and gas reservoirs, their source rocks, and intervening formations.

WSGS geologists examined more than 2,200 oil and gas wells throughout the Powder River Basin—chosen based on location and quality of available data—to identify and correlate key stratigraphic horizons from the Lower Cretaceous Muddy Sandstone through the Upper Cretaceous Fox Hills Sandstone. These formations were deposited about 100–70 million years ago in a shallow sea that covered much of central and western North America.

Interpretations of depth-to-formation in the su

“In 2019, more than 60 percent of Wyoming’s oil production was from reservoirs in the Powder River Basin,” says WSGS Director and State Geologist, Dr. Erin Campbell. “Understanding the thickness and distribution of these hydrocarbon reservoirs and source rocks—and especially making the data public—should help guide future exploration throughout the basin.”bsurface, or “formation tops,” were used to develop type logs and create contour maps of formation depth and thickness. The contour maps illustrate how each formation changes throughout the basin, and provide insight into the depositional, structural, and hydrocarbon development history of this important oil- and gas-producing region.

The formation tops and associated well data are the first dataset to populate a new, publicly available database of Wyoming’s subsurface geology. This enterprise relational database has been incorporated into the WSGS Interactive Oil and Gas Map of Wyoming, where users can view the formation tops and contour maps alongside other Powder River Basin wells, oil and gas fields, and infrastructure. The well data and formation tops are downloadable in tabular format directly from the interactive map. Any future corrections to the dataset will be entered into the WSGS database and automatically updated in the interactive map. A supplementary geodatabase, containing a snapshot of the contour maps, wells, and formation tops used at the time of this study, is also available for download (click the supplemental data button).

“The data behind the stratigraphic interpretations made in this study are freely available. It was our goal to provide the public, industry, and researchers with the sort of detailed, quality-controlled dataset crucial for further inquiry into the Upper Cretaceous geology of northeastern Wyoming,” says WSGS oil and gas geologist Derek Lichtner.

Open File Report 2020-9, Upper Cretaceous Strata in the Powder River Basin: Formation Tops Database, Structure and Thickness Contour Maps, and Associated Well Data, is available as a free download. The WSGS welcomes input and discussion, as its geologists hope to continually refine and expand the 

dataset..