Fault-induced fluid migration and mineralization along major faults; Mohawk Valley, NYS as an outcrop analog for the Trenton/Black River gas plays in the Finger Lakes region, NYS
Agle, Paul A.
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The recent success of the Trenton/Black River (T/BR) natural gas plays has renewed industry interest in the Appalachian Basin of New York State. These natural gas plays are hosted within narrow dolomitized fairways in the Upper Ordovician carbonate platform. These "sweet spots" are structurally controlled by the presence of faults that have acted as conduits for migration of dolomitizing fluids through the section. This study addresses the issues of which orientation(s), offset type(s), and timing(s) promoted the fluid migration associated with the creation of secondary porosity within the otherwise non-porous limestones. For purposes of this study, the Cambro-Ordovician carbonates exposed in the Mohawk Valley near Little Falls, NY, are used as an analog for the reservoir rocks at depth elsewhere in the state. The study also analyzes features in an 11.28m (37ft) long oriented, horizontal core taken from a producing gas well in the region of active exploration and production. The field research uses fracture orientations, abutting relationships, and lithologic mapping to determine the relative timing of the fracturing and faulting in the Mohawk Valley region. The study also examines the relationship between faulting and mineralization features (e.g., vugs, veins, and dolomitization) in the field area. The research involving the horizontal core evaluates many of these same features at depth in the producing region. A suite of geochemical analyses performed on veins of various orientations and stratigraphic horizons determines how the chemistry of the mineralizing fluid is related to those two variables. This integration of readily available surface outcrop data and core data allows the development of a model of fluid migration and porosity development to aid in the exploration of New York State's untapped hydrocarbon reservoirs.