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This study, a stratigraphic subsurface analysis of the Ravencliff sandstone, attempted to determine the depositional environments, depositional history, and paleogeography of the interval. Gas production was compared to thickness, position on sand trends, shale content, porosity, and structural position to determine the effect that these have on the Ravencliff gas production.
The study area includes 1,037 mi2 (2,686 km2) from the subsurface of southern West Virginia counties of McDowell, Wyoming, and Mercer.
The interval studied is a member of the Hinton Formation of the Mauch Chunk Group. This Ravencliff interval is bounded below by the Avis Limestone, a marine unit, and bounded above by a black, carbonaceous shale. Thickness of the interval ranges from 150 ft (45 m) in northwestern Wyoming County to 450 ft (137 m) in southeastern Mercer County.
Petrographically, the Ravencliff sandstone is a clean white sandstone showing well-rounded grains and pebbles and commonly containing more than 90% quartz. Examination of three cores from the area reveals an orthoquartzitic sandstone with conglomeratic and pebbly zones throughout. Unidirectional, high-angle cross-bedding was prevalent throughout all of the cores.
Twenty-three cross sections were constructed and show multiple stacked sandstones up to 150 ft (45 m) thick. Lithofacies, isopach, and isolith maps of the interval and individual sandstones reveal a series of northeast-southwest sandstone trends.
The Ravencliff interval is interpreted to represent a regressive phase of deposition from the marine Avis Limestone to the fluvial-deltaic environment of the Ravencliff sandstones. Source areas for the Ravencliff system are believed to be northeast of the study area.
The first phase of the Ravencliff fluvial-deltaic system was the erosion and subsequent filling of a major northeast-trending valley. Tributary systems perpendicular to this valley became incised in the underlying Avis Limestone and provided feeder systems into this major upper deltaic-plain valley.
Subsequent to the filling of the major valley, the Ravencliff system went through periodic avulsions in an aggradational lower deltaic-plain environment. These fluvial-deltaic systems, in some areas, accumulated over 120 ft (37 m) of recognizable channel sandstone.
Gas production appears to be controlled by a variety of factors, including sandstone thickness, shale content, and diagenetic loss of primary porosity.
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