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Regional Stratigraphic and Reservoir Investigation of the Beekmantown Dolomite and Equivalent Units (Cambrian-Ordovician) in Ohio, Pennsylvania, and New York

R. A. Riley
Representing the Beekmantown Research Consortium and the Ohio Division of Geological Survey, Columbus, OH

The Beekmantown Research Consortium, partially funded by NYSERDA, conducted a regional investigation of the Beekmantown dolomite and equivalent units across eastern Ohio, western Pennsylvania, and western New York. The primary goal was to better understand the regional stratigraphy, lithology, depositional environment, and post-depositional processes controlling porosity development in the Beekmantown dolomite, and relate them to hydrocarbon production.

While Beekmantown production in the Appalachian basin has been confined to eastern Ohio, porosity development and hydrocarbon shows indicate oil and gas potential exists throughout the study area. Regional correlations from wireline logs, cores, and well cuttings indicate up to 3 distinct zones of porosity development in the Beekmantown dolomite (informally named the “A, B, and C porosity zones”) that are related to multiple episodes of subaerial exposure. These porosity zones can be correlated across much of eastern Ohio and more tenuously into western Pennsylvania and New York. An FMS image from a producing Beekmantown well in Guernsey County, Ohio indicated caves up to 3 feet in diameter in the “B porosity zone.” Regional core examination of the “A and B porosity zones” indicates vugs up to 4 inches across commonly filled with secondary dolomite. Many of these areas of porosity are associated with crackle, chaotic, and mosaic breccias. Local occurrences of anhydrite within the “A and B porosity zones” indicate that dissolution of evaporites, in part, controlled porosity development.

Beekmantown deposition occurred in a tidal flat to shallow marine environment along a broad continental shelf. Carbonates are dominant, and siliciclastics become more common to the northeast in Pennsylvania and New York. Locally, evaporite deposition occurred in areas of restricted circulation and elevated salinity. Multiple episodes of subaerial exposure of Beekmantown deposits created early diagenetic porosity.

AAPG Search and Discovery Article #90900©2001 AAPG Eastern Section Meeting, Kalamazoo, Michigan