The Upper Devonian Rhinestreet Shale: An Unconventional Fractured Reservoir in Western New York State*
Gary G. Lash1
Search and Discovery Article #10108 (2006)
Posted August 10, 2006
*Oral presentation at AAPG Annual Convention, Houston, Texas, April 9-12, 2006
1SUNY-Fredonia, Fredonia, NY (Lash@fredonia.edu)
The Upper Devonian Rhinestreet Shale of western New York State comprises a sequence of finely laminated, low-permeability, organic-rich shale and thin intervals of gray shale and concretionary limestone. The Rhinestreet thickens from ~54 m in exposure along the Lake Erie shoreline to >100 m near the Pennsylvania-New York border where its burial depth >1100 m. Total organic carbon content of the Rhinestreet along the lake shore attains a maximum of 8% and appears to remain high to the south in the subsurface, based on the analysis of gamma-ray and bulk-density logs. To the east, however, the thickness of the organic-rich interval decreases as siltstone and organic-lean gray shale become more abundant. Measured vitrinite reflectance (0.76%) and Rock-Eval Tmax (443o C) values place the exposed Rhinestreet shale squarely within the oil window. The Rhinestreet carries several sets of vertical joints interpreted to have formed as gas-driven natural hydraulic fractures during Paleozoic catagenesis. The joints, open in outcrop, are likely closed at depth under progressively higher confining pressure. Exceptions to this may be those joints oriented subparallel to the contemporary maximum horizontal stress field (ENE). Some organic-rich clay layers carry horizontal µm-scale microcracks, most of which are filled with bitumen, thereby contributing to the low permeability of these rocks. However, in those areas of the basin where the Rhinestreet may have entered the gas window, cracking of the bitumen to gas would have led to enhanced storage of free gas. The great unknown, then, remains the level of thermal maturity of the Rhinestreet Shale in the subsurface to the south and east of Lake Erie.