--> Abstract: Assessment of Undiscovered Natural Gas Resources in Devonian Black Shales, Appalachian Basin, Eastern U.S.A., by Robert C. Milici; #90039 (2005)

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Assessment of Undiscovered Natural Gas Resources in Devonian Black Shales, Appalachian Basin, Eastern U.S.A.

Robert C. Milici
U.S. Geological Survey, Reston, VA

The U.S. Geological Survey recently assessed the undiscovered continuous hydrocarbon resources of the Devonian shale as part of its Appalachian Basin assessment. The assessed Devonian shale constitutes the distal deposits of the Catskill delta from New York to West Virginia, Ohio, and eastern Kentucky. The Devonian shale was divided into four assessment units (AUs): the Northwestern Ohio Shale (NWOS), Greater Big Sandy (GBS), Devonian siltstone and shale (DSS), and the Marcellus Shale (MS). Together, they contain 12.2 TCFG and 159 MMBNGL at the statistical mean. The AUs were defined by the net thickness of radioactive black shale (RBS), thermal maturity, and stratigraphy.

The NWOS AU contains up to 400 ft of RBS and is thermally immature. The strata consist of fine-grained turbidites. Fracture porosity is related to regional geologic structures and to areas of glacial rebound.

In the GBS AU, the most productive, net thickness of RBS is up to 500 ft; the area is thermally mature. Fracture porosity is enhanced by geologic structure. Total organic carbon (TOC) in the black shale averages 2-3 percent.

The DSS AU contains siliciclastics that are coarser grained than those to the west. Net thickness of RBS ranges from 200 ft in West Virginia to 500 ft in New York. The AU is thermally mature.

The MS AU is the basal black shale unit of the Catskill delta. Net thickness of thermally mature RBS is about 100 ft in Pennsylvania and TOC values are as high as 11 percent. This AU is relatively untested.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005