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The AAPG/Datapages Combined Publications Database

Williston Basin Symposium

Abstract

MTGS-AAPG

Seventh International Williston Basin Symposium, July 23, 1995 (SP12)

Pages 115 - 128

A Preliminary Comparison of Waulsortian Mound Facies in the Williston and Illinois Basins

Randolph B. Burke, North Dakota Geological Survey
Zakaria Lasemi, Illinois State Geological Survey

ABSTRACT

Mississippian age Wauisortian-like mounds have been identified in the lower Lodgepole Formation in the Williston Basin and in the Fort Payne and Ullin ("Warsaw") Formations in the Illinois Basin. The location of the Williston mounds is associated with fault zones believed to have been active at various times during the Phanerozoic. A similar tectonic control for the development of the Illinois mounds has not been established.

Mounds in Illinois apparently developed on a ramp setting, but the only known petroleum productive mound in the Williston is interpreted to be on the basin floor at the toe of the shelf slope, or ramp. Williston mounds are Kinderhookian in age, older than the lower Meramecian-upper Osagean Illinois mounds. The mounds in both basins are lithologically similar with crinoids and bryozoans as the dominant skeletal components. Although stromatactis are common in the mounds in both basins, those in Illinois are cemented with silica rather than the calcite cement common in the Williston.

Oil production in the Williston Basin comes from the mound core facies. In contrast, oil production in the Illinois Basin comes from bryozoan-dominated bioherms and grainstone shoals overlying the mound complexes. Basinal mounds in the Williston have average estimated primary reserves of 2.5 MMBO per well and mid-ramp buildups in Illinois have average estimated reserves of 90,000 BO per well.

The differences indicate potential new play opportunities for each basin. In the Williston Basin, shallow shelf-slope or ramp buildups are probable, and, in the Illinois Basin, deep basin or lower ramp mounds are likely. Discovery of more hydrocarbon reserves in the Waulsortian facies in both basins will depend on increased understanding of the variability of Waulsortian-like buildups and their oil production characteristics.

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