SHURR, GEORGE W.
GeoShurr Resources, LLC, Ellsworth, MN

Abstract: Basin Margin Gas Plays

Shallow natural gas accumulations are found around the margins of at least eight mature basins in North America. Initial production was generally early in the history of basin exploration and wells usually had low delivery rates. However, shallow depth and wide distribution make basin margin gas plays important "rediscovery" opportunities for independents employing modern technology.

Basin margin gas is biogenic gas associated with immature source rocks. On the margins of the Michigan Basin, the Devonian Antrim Shale may have had methanogenesis during the Pleistocene (Martini et al., 1996) and similar suggestions have been made for gas in the New Albany Shale on the Illinois Basin margins. Additional examples of basin margin gas from Paleozoic rocks are found in the lake shore fields of the northwestern Appalachian Basin and in the Hugoton Embayment of the northern Anadarko Basin. Basin margin gas occurs in Cretaceous rocks in several Rocky Mountain basins including the Niobrara Chalk in the northeastern Denver Basin, the Muddy and Shannon Sandstone in the northeastern Powder River Basin, and the Medicine Hat and Milk River units in the southeastern Alberta Basin.

Characteristic attributes of basin margin gas are well illustrated in Cretaceous rocks in the Williston Basin of Montana, North Dakota, and South Dakota. The gas is found in a variety of reservoirs ranging from conventional reservoirs in fluvial and coastal sandstones to low contrast, low resistivity reservoirs in marine clastic shelf facies. Structural control is important at the scale of regional arches down to fracture patterns within fields. Gas compositions show patterns of nitrogen variation that may be related to ground water transport.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas