Geology

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The Pennsylvanian Black Shale 

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The younger of two subperiods of the Carboniferous Period (or the upper of two subsystems of the Carboniferous System). It lasted from roughly 323.4 million years ago to 298.9 million years ago. The Pennsylvanian is named after the U.S. state of Pennsylvania, where the coal beds of this age are widespread.

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The division btween Pennsylvanian and Mississippian comes from North American stratigraphy. In North America, where the early Carboniferous beds are primarily marine limestones, the Pennsylvanian was in the past treated as a full-fledged geologic period between the Mississippian and the Permian. In parts of Europe, the Mississippian and Pennsylvanian are one more-or-less continuous sequence of lowland continental deposits and are grouped together as the Carboniferous Period. The current internationally used geologic timescale of the ICS gives the Mississippian and Pennsylvanian the rank of subperiods, subdivisions of the Carboniferous Period.

 

As of 2013 the Cline Shale, also referred to as the "Wolfcamp/Cline Shale", the "Lower Wolfcamp Shale", or the "Spraberry-Wolfcamp shale", or even the "Wolfberry" is a promising Pennsylvanian oil play east of Midland, Texas which underlies ten counties: Fisher, Nolan, Sterling, Coke, Glasscock, Green, Howard, Mitchell, Borden and Scurry counties. Exploitation will rely on hydraulic fracturing.

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Wolfcamp formation deposited during late Pennsylvanian through late Wolfcampian time is distributed across the entire Permian Basin. The Wolfcamp formation is a complex unit consisting mostly of organic-rich shale and argillaceous carbonates intervals near the basin edges. Depth, thickness, and lithology vary significantly across the basin extent. Depositional and diagenetic processes control this formation heterogeneity.

 

Stratigraphically, the Wolfcamp is a stacked play with four intervals, designated top-down as the A, B, C, and D (Cline Shale) benches (Gaswirth, 2017). Porosity of the Wolfcamp Formation varies.