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The AAPG/Datapages Combined Publications Database

Ohio Geological Society

Abstract

OGS-AAPG

Ohio Geological Society: Major Natural Gas Plays of the Appalachian Basin of Ohio and Surrounding Areas: Second Annual Technical Symposium, October 19, 1994

Pages 98- 120

CAMBRIAN-ORDOVICIAN KNOX UNCONFORMITY GAS RESERVOIRS IN THE APPALACHIAN BASIN. *

Ronald A. Riley, Ohio Division of Geological Survey
Mark T. Baranoski, Ohio Division of Geological Survey
Mark E. Wolfe, Ohio Division of Oil and Gas, Columbus, Ohio

Abstract

Productive gas pools and fields in the Cambrian-Ordovician Knox Group unconformity play occur in linear to broad trends from northern Tennessee to south- central Kentucky, through central and northern Ohio, and extend in very localized areas of northwestern Pennsylvania and western New York. In northern Tennessee and south- central Kentucky production is from the Beekmantown dolomite. Copper Ridge dolomite production is also present in eastern Kentucky. In Ohio Knox production occurs in the following units in descending stratigraphic order: Beekmantown dolomite, Rose Run sandstone, Copper Ridge dolomite (Trempealeau of drillers), stray sandstones in the upper Copper Ridge Dolomite, and the B zone and Krysik sandstone of the lower Copper Ridge Dolomite. Hydrocarbon production also occurs in the upper sandy member of the Gatesburg (Rose Run equivalent) in northwest Pennsylvania and in a sandstone unit of the Theresa Formation (partial Rose Run equivalent) in New York.

Primary trapping mechanisms for Knox units include paleotopographic highs (erosional remnants), vuggy porosity zones, faults and associated fractures, stratigraphic updip truncations against the Knox unconformity, and basement-related structures. In Ohio paleotopographic highs dominate the producing trends. In south-central Kentucky and northern Tennessee, paleotopography is important, but fracturing seems to play a more dominant role in production. Gas production in the upper sandy member of the Gatesburg Formation in northwest Pennsylvania is influenced by a combination of structural fault control and stratigraphy.

Production decline curves for Ohio wells exhibit three reservoir variations: Beekmantown dolomite, Rose Run sandstone, and Copper Ridge dolomite. The Beekmantown dolomite of the Bakersville field shows the greatest average cumulative gas well production at 680 million cubic feet (MMcf) after ten years. Average cumulative gas well production after 10 years in the Rose Run sandstone is 400 MMcf. The Copper Ridge Dolomite average cumulative gas well production after 10 years is estimated at 170 MMcf.

The Knox play continues to have great potential, particularly in the western part of the Appalachian basin. Large areas of the basin remain untested for Beekmantown dolomite within and downdip from the Rose Run subcrop trend. The Rose Run sandstone reservoirs (and equivalent upper sandy member of the Gatesburg Formation and Theresa Formation) are attractive targets along the entire subcrop trend from south- central Ohio to northwestern Pennsylvania and into western New York. High-risk and high-potential also exists in the upper sandy member of the Gatesburg Formation in the Rome trough in Pennsylvania and West Previous HitVirginiaTop. The sparsely drilled B zone and Krysik sandstone of the Copper Ridge dolomite holds much potential, especially where this unit is a well-developed thick reservoir in central and north-central Ohio. Knox potential also exists within fracture zones along major fault trends such as the Akron-Suffield and Highlandtown fault systems. Production from paleotopographic highs and fractured Knox reservoirs of southern Kentucky and northern Tennessee continues to hold potential.

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