WSGS Investigates Oil and Natural Gas Production in the Wall Creek and Turner Reservoirs in Southern Powder River Basin

Geology influences oil and natural gas production from the Wall Creek and Turner reservoirs in Wyoming’s Powder River Basin more than well completion techniques, according to a new study by the Wyoming State Geological Survey (WSGS).

The Upper Cretaceous Wall Creek Sandstone Member of the Frontier Formation and the Turner Sandy Member of the Carlile Shale (Wall Creek-Turner) is one of the most prolific unconventional plays in Wyoming. In the last two years, nearly one-fifth of the state’s approved permits to drill have been for wells targeting this reservoir system, with most permitting and drilling activity occurring in southern Campbell and northern Converse counties.

“It is important for the Survey, and the state as a whole, to understand the drivers of production from the Wall Creek-Turner reservoir because more than 23 percent of all oil produced in Wyoming in 2018 came from this reservoir,” says WSGS Director and State Geologist, Dr. Erin Campbell. “Many protested applications heard before the Wyoming Oil and Gas Conservation Commission involve these formations. This report can help the commission make decisions that best benefit Wyoming in terms of efficient and highly productive drilling.”

Report of Investigations 77—Influences on Oil and Natural Gas Production from the Wall Creek and Turner Sandstone Reservoirs, Powder River Basin, Wyoming—examines if and how the techniques used to drill and complete horizontal wells in the Wall Creek-Turner affect oil and natural gas production. Horizontal well attributes evaluated in this study include producing interval length, lateral orientation, hydraulic fracturing stage, slurry and proppant volume, and operator-specific trends over time.

Wall Creek-Turner production trends are spatially and statistically compared to reservoir geologic characteristics, including depth, thickness, pressure, temperature and regional structural features, as well as hydrocarbon composition such as crude oil gravity, gas-oil ratio, and natural gas carbon fraction.

“This study reinforces the complexity of the Wall Creek-Turner reservoir system,” says WSGS oil and gas geologist and author, Rachel Toner. “It appears that the location of a horizontal well in the Wall Creek-Turner, especially in regards to the reservoir depth and temperature, is a better predictor of production success than well design. Spatial interpolations between existing gas-oil ratio, oil gravity, and reservoir temperature datasets may also indicate where productive areas could be found in as-yet undeveloped portions of the reservoir.”

The 84-page publication is accompanied by an Excel spreadsheet of point data used in the investigation. Also available is a supplementary geodatabase and interactive online map that includes the study’s raster surfaces, associated contour lines, and wells used to create the surfaces.