An Initial Assessment of the Point Pleasant and Utica Reservoirs in Eastern Ohio
Bowker, Kent A.
The Point Pleasant Formation and, secondarily, the Utica Shale have recently become major exploration targets on the northwestern limb of the Appalachian basin (eastern Ohio and western Pennsylvania). The Ordovician Point Pleasant is stratigraphically located above the Trenton Group and below the Utica. Both contacts are gradational in core examination but are rather sharp on wireline logs.
The Point Pleasant is a calcareous shale, much like the Eagle Ford Shale of south Texas. But unlike the Eagle Ford, the Point Pleasant contains scores of thin (about ¼ to 2 inches thick), white, porous and permeable limestone beds (mostly packstone). These thin beds are composed of broken shell material (brachiopods, trilobites, crinoids) that were washed down into the deeper depositional basin by storms or other events from the shallower shelf. These thin limestones, with a permeability of up to 20 md, act as horizontal "superhighways" within the reservoir and can connect the vertical hydraulic fractures created during completion to form a permeability lattice within the reservoir. Recently-reported very high production rates support this contention. The Utica contains relatively few of these thin limestone beds.
The organic-rich shale portions of the Point Pleasant also contain excellent porosity and permeability, on par with the Eagle Ford Shale. There is a quadruple porosity system in the shale sections of the Point Pleasant: porosity in the abundant organic matter, within grains, within particles of clay, and between the grains. Porosity ranges from 3 to 5% and water saturation ranges from 40 to 60% in the Utica. In the Point Pleasant, porosity ranges from 4 to 7% and water saturation from 15 to 30%. The low water saturation in the Point Pleasant is probably the cause of the shale's ultra-high resistivity (>1000 Ω ). Many operators in the play currently shut wells in immediately following fracture stimulation because it appears this increases hydrocarbon production. The low water saturation may help explain why this is a successful practice.
The organic matter within the Utica/Point Pleasant is lipid rich and very oil prone (HI >900 in immature samples). Given the age of the rocks, this is not unexpected. Point Pleasant oil does not fluoresce nor does it have an odor. The usual tools we use for measuring thermal maturity and how thermal maturity relates to hydrocarbon type present in the rock both need to be adjusted in this play.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013