Oriskany Sandstone lithofacies, paleoenvironment, and fracture porosity in Somerset County, Pennsylvania
The Lower Devonian Oriskany (Ridgeley) Sandstone is an important deep exploration target in the Appalachian basin. Petrographic examination of two drill cores of the Oriskany-Needmore Shale interval from south-central Somerset County indicates that identifiable lithofacies of the upper Oriskany Sandstone exist in the subsurface. Oriskany lithofacies are defined as silica-cemented quartzarenite, sandy biosparite, calcareous-cemented quartz wacke, and coquinoid calcareous-cemented quartzarenite. These lithofacies are interpreted as depositional features of a shallow marine sand-bar complex, corresponding to central-bar, bar-margin, interbar, and storm-generated sheet-sand (tempestite) depositional units. Paleoenvironmental interpretations are supported by diagnostic trace-fossil assemblages and coarsening-upward grain size trends indicative of vertically stacked marine bars. Correlation of ..gamma..-ray logs from Oriskany wells across Somerset County suggests that these marine bars are laterally discontinuous and may change abruptly in thickness over relatively short distances. Fracture porosity occurs primarily in the silica-cemented quartzarenite lithofacies, or central-bar paleoenvironmental unit. The quartzarenite lithofacies is recognizable on ..gamma..-ray logs by its blocky, low API unit signature at the top of sequences that exhibit a downward increase in shale content. As the presence of fracture porosity is important in Oriskany natural gas production in this region, central-bar units are primary targets for exploration.
- Research Organization:
- Univ. of Pittsburgh, PA
- OSTI ID:
- 5741529
- Report Number(s):
- CONF-8410269-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Vol. 68:12; ISSN AAPGB
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
030200* -- Natural Gas-- Reserves
Geology
& Exploration
DEVONIAN PERIOD
EXPLORATION
FEDERAL REGION III
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
LITHOLOGY
MINERAL RESOURCES
NATURAL GAS DEPOSITS
NORTH AMERICA
PALEOZOIC ERA
PENNSYLVANIA
POROSITY
RESERVOIR ROCK
RESOURCES
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
USA