Mineralogy, microfabric and pore evolution in late-middle Ordovician mudstone of the Utica/Point Pleasant sub-basin of Ohio, West Virginia, and Pennsylvania

The Utica/Point Pleasant Formations comprise a major unconventional gas resource in the Appalachian Basin. Core samples from several boreholes Ohio, West Virginia and Pennsylvania were studied to determine mineralogy, microtexture/microfabric, accessible pore surface area, porosity size distribution as function of maturity sub-basin. This effort compares shallower, generally more phyllosilicate-rich Utica intervals with deeper, carbonate-rich Point intervals, latter representative horizons currently targeted for recovery. Formation contains mostly calcite (in form fossil tests, grains, cements), distributed within alternating carbonate- matrix laminae, well coarse-grained fossil-rich laminae. In both core samples, greatest mercury-accessible connected measurements are associated highest an observation that is particularly pronounced Pleasant. More detailed vertical sampling analysis Harrison County, Ohio (a region has experienced copious shale production) shows volume connectivity increase locally target identified Observations suggest optimal mixtures arrangements minerals organic matter, increasing maturity, contribute forming this productive resource. particular, early diagenetic quartz cement quantities silt-sized particles higher measured porosities, while later-stage dolomitization recrystallization laminae tend occlude network.