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ABSTRACT: Petrophysical Analysis of the Upper Copper Ridge Dolomite, Richland and Northern Ashland Counties, Ohio

DAUGSTRUP, ERIC K., University of Akron, Akron, OH

The reservoir quality, textural characteristics, and typical well log response of the Cambrian, Upper Copper Ridge Dolomite, in northern Ashland and Richland Counties, Ohio, was determined. It is composed of nonplanar dolomite with planar-e and planar-s void fill. Detrital 0.05 mm subangular quartz and feldspar is a major component in northern Richland and Ashland Counties, but is rare in southern Richland County. Intercrystalline and vuggy porosity are the most abundant porosity types in southern Richland County, while intercrystalline and intergranular porosity are most abundant in northern Richland and Ashland Counties. Porosity development increases with an increase in planar-e, and planar-s dolomite. In southern Richland County the reservoir quality is controlled by diagenetic ev nts. Authigenic illite and baroque dolomite occlude porosity. Illite infilling up to 95% of porosity, causes higher than normal porosity values in the neutron log. In northern Richland and Ashland Counties, reservoir quality is controlled by depositional factors: mainly detrital silt content, and shale distribution.

The geophysical log response for the Knox unconformity is characteristic. The gamma ray/neutron response is sharp in response to a sharp unconformity. Where a gradational unconformity is present, log response is also gradational on the gamma ray/neutron log. The top of the "B-zone" is defined as a thin, continuous shale bed within the study area, based on core and well log relationships. The silty dolomite characteristic of the Upper Copper Ridge in northern Richland and Ashland Counties is not "B-zone," as illustrated by geophysical log correlation.


AAPG Search and Discovery Article #91013©1992 AAPG Eastern Section Meeting, Champaign, Illinois, September 20-22, 1992 (2009)