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Devonian and Mississippian Hydrocarbon Generation and Migration in Southern West Virginia, Appalachian Basin

McCallum, Scott *1; Willan, Chris 1
(1) EQT Production, Pittsburgh, PA.

The primary objective of this study was to gain an understanding of the fluid network and connectivity of the Devonian and Mississippian system (DMS) in southern West Virginia. This analysis led to a conceptual model describing hydrocarbon generation and migration as well as the present day pressure regime within this system.

The primary data include fluid inclusion, pressure, aquifer, and chemical tracer data sets. Many of the data sets are seemingly unrelated to one another, but taken as a whole are informative for understanding the mechanisms of hydrocarbon generation and migration. The data was interpreted using both statistical analyses and geologic mapping.

Possible hydrocarbon sources include the Rhinestreet, Dunkirk and Sunbury intervals. Based on TOC, maturity and thickness data the Dunkirk is the primary source, although some degree of mixing from the Rhinestreet and Sunbury is likely. The high degree of statistical similarity between the fluid inclusions of the Greenbrier and Onondaga, which are separated by 3000 feet, imply that both intervals were charged by the same or very similar fluids. Unique pressure compartments are not evident based on the pressure data. Review of USGS aquifer mapping supplemented by water saturation calculations indicates that the overlying aquifer is regionally extensive and coincidental with the top of the modern gasifer. The chemical tracer data was characterized by rapid vertical and lateral communication with the offset monitoring wells, which is indicative of present day connectivity.

The conceptual model derived from the data indicates that the DMS in southern West Virginia has likely gone through several phases of development. Prior to the Mississippian the system was normally pressured and water saturated. At the onset of liquid hydrocarbon generation during the Pennsylvanian, water was flushed or partially flushed from the system and the pressures were normal to over-pressure. Maximum burial after the Alleghenian orogeny led to thermal cracking from liquid hydrocarbon to gas during Permian time. This resulted in the DMS becoming over-pressured, thereby further flushing a bulk of the remaining water. Subsequent hydrocarbon leakages resulted in the present day system defined by an under-pressured gasifer overlain by a normally pressured aquifer.


AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California