Deposystem Analysis and Reservoir Geometry of the Pennsylvanian Pottsville Group Near Ironton, Ohio

Hamrick, Terry¹ and Ronald Martino^2
1 Natural Resource Partners, LP, Huntington, WV
² Marshall University, Huntington, WV

Lithofacies analysis and fossil assemblages in the vicinity of Ironton, Ohio and Greenup, Kentucky indicate deposition in marginal marine environments dominated by estuarine and tidal flat processes. Clastic lithofacies can be placed into five groups that define reservoir geometry and genesis. Facies groups are based on genetic units found within the estuarine depositional system. Estuarine sediments of the Pottsville Group can be described as 1) fluvio-estuarine transitional channel sandstones, 2) upper estuary alluvial plain sandstones, 3) tidal sand flats, 4) mud and mixed flats, 5) marine and brackish - water silty shale.

Each subsystem of the estuarine environment exhibits a unique geometry and lithology, or range of lithologies, that is easily studied in the Ironton area. Fluvio-estuarine sandstones 1.5 – 5.0 meters thick exhibit channel-form geometry within bedrock-confined valleys. Upper estuarine deposition is represented by large-scale meandering channel sandstones 5.0-12.0 meters thick occupying the head of the embayment. Tidal sand flats are typically ripple and flaser bedded sandstones up to 4 meters thick. Distribution is limited to belts between the subtidal channel and low energy intertidal mud flat environments.

This outcrop investigation will aid in understanding local depositional systems and genetic units of the Pottsville Group. Knowing the characteristics and genesis of each unit will help facilitate nearby exploration where oil and gas production occurs from relatively shallow reservoirs. Despite active production, there have been few studies that help define the overall character and distribution of producing Pottsville reservoirs.

AAPG Search and Discovery Article #90031©2004 AAPG Eastern Section Meeting, Columbus, Ohio, October 3-5, 2004