Abstract: Overview of Shallow Gas Production from Eagle-equivalent Rocks South and East of Cedar Creek Anticline

George W. Shurr

Shallow gas has been produced for more than fifty years from Eagle-equivalent Cretaceous sandstones on Cedar Creek Anticline in eastern Montana. In the last two decades four fields have been developed off the south: and east flanks of the anticline: 1) West Short Pine Hills and 2) Cady Creek in Harding County, SD; 3) Gaslight; in Fallon County, MT; and 4) Little Missouri in Bowman County, ND.

Paleogeographic reconstructions indicate that the reservoir rocks in all four fields were deposited near an outer shelf margin more than 200 mi (322 km) east of the strandline. West Short Pine Hills and Cady Creek Fields are located within a sandstone sheet up to 15 ft (4.6 m) thick. Gaslight Field is near the margin of the sheet and has thinner sandstones. In Little Missouri Field the reservoir is primarily interbedded siltstone and shale.

Regional lineament zones mapped on satellite images influenced Cretaceous deposition and were also the sites of post-depositional deformation. The South Dakota gas fields are located within a tectonic block well away from bounding lineament zones. Gaslight is within a northeast-trending lineament zone and Little Missouri is at the intersection of lineament zones trending northeast and northwest.

Production in Little Missouri Field is clearly influenced by structure. Values of initial production and marker-bed elevation show a strong correlation. Wells with large IP values are found along the crest of a small anticline and show steeper decline curves than wells with small IP values at the margins of the structure. In contrast, IP values show little correlation with structural altitude in the gas fields of South Dakota and Montana.

AAPG Search and Discovery Article #90952©1996 AAPG Rocky Mountain Section Meeting, Billings, Montana