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High Matrix Porosity in a Dolomitized Black River Reservoir, Clinton County, Kentucky

David C. Harris1, John B. Hickman1, and Jesse Kincheloe2

1Kentucky Geological Survey, University of Kentucky, Lexington, KY 40506

2Consultant, Campbellsville, KY 42718

Ordovician oil reservoirs in the Black River (High Bridge) Group (Stones River, Murfreesboro of drillers) in south-central Kentucky commonly occur in fractured limestone. High-volume oil producers like the 1990 Syndicated Options No. 9372 Ferguson Brothers well in Clinton County are rare, and predicting these fractured reservoirs remains difficult.

Little reservoir data were obtained when the 9372 well was drilled. Oil production declined rapidly, and the well was later deepened. Subsequent logging revealed two fractured limestone zones. Surprisingly, wells drilled near the 9372 discovery penetrated an unusual zone of high matrix porosity in the lower Black River and Wells Creek. This narrow, linear oil reservoir, penetrated by 12 wells to date, occurs immediately above the Knox unconformity and is oriented northeast-southwest. It is at least 2,400 ft long, 150-200 ft wide and up to 250 ft thick. The zone is characterized by log-derived porosity of up to 30 percent. Neither well samples nor core are available from this interval, but log data indicate the porous interval is dolomitized.

Interpretation of seismic reflection data over the trend indicates it lies above a deep-seated fault zone, suggesting the porosity may be fault-controlled. The zone cuts across a larger structural low mapped at the Knox, Black River, and Devonian Chattanooga Shale levels. The origin of the dolomite and associated porosity may be related to Mississippi Valley-type hydrothermal mineral deposits in south-central Kentucky. The Ferguson trend, which has produced at least 650,000 barrels of oil, indicates the Black River dolomite play extends into south-central Kentucky.

AAPG Search and Discovery Article #90059©2006 AAPG Eastern Section Meeting, Buffalo, New York