The Upper Devonian Rhinestreet Shale, Western New York State: From Seal to Fractured Reservoir
Gary G. Lash
SUNY-Fredonia, Fredonia, NY
The Upper Devonian Rhinestreet black shale of the Catskill Delta complex, western New York State, reflects a complex burial and overpressure history that resulted in the generation of multiple sets of vertical joints interpreted to be natural hydraulic fractures (NHFs). The EASY%Ro chemical kinetic model was used in this study to model an average vitrinite reflectance value of 0.76% measured on samples collected from along the Lake Erie shoreline. The earliest set of joints, a NS-trending set, is found almost exclusively at the contact of the Rhinestreet shale and underlying Cashaqua gray shale indicating that the former served as a hydraulic top seal at the modeled burial depth of ~2.1 km and prior to the onset of catagenesis (modeled Ro=0.50%). The pre-catagenic NHFs that propagated from the top of the Casahqua gray shale into the base of the Rhinestreet shale may have initiated during uplift of the basin caused by the Morrowan docking of the Goochland terrane in the southern Appalachians. A renewal of subsidence during the Atokan carried the Rhinestreet into the oil window by the Middle Permian (modeled Ro=0.60%) when bitumen-filled horizontal μm-scale microcracks propagated through these laminated, low-permeability deposits now pressurized by catagenesis. Soon after this, NW-trending vertical NHFs formed within the Rhinestreet, especially its organic-rich basal interval. Thus, those characteristics of the Rhinestreet that enabled it to serve as an efficient top seal favored its hydraulic fracturing during catagenesis. The final phase of NHF generation, an ENE-trending set, probably occurred near the end of the Permian in response to Alleghanian dextral tectonics and at the modeled maximum burial depth of ~ 3.2 km.