UTICA SHALE DEPOSITION IN THE TACONIC FORELAND BASIN: EVOLUTION AND THE POTENTIAL FOR NATURAL GAS PRODUCTION

One of the oldest and most widespread black shales is the Utica Shale. It was deposited very broadly across the Appalachian Basin and covers thousands of square miles. In New York, depth varies from outcrop to depths over 9,000 feet in the southern portion of the state. Thickness varies from tens of feet in the west to over 1,000 feet in the east.

The Utica is a massive, fossiliferous, organic-rich, thermally-mature black to gray-black shale, and is considered to be the source rock for Lower Devonian through Cambrian hydrocarbon production and shows. The shale was deposited in a deep marine basin with a subsiding trough that generally trended north-south. It interfingers with the basal Dolgeville Formation, which is composed of alternating beds of limestone and shale. Source rock for the organic-rich black shale was supplied from the eroding Taconic highlands to the east. As the deep marine trough was filled in, the deposition of the upper formations of the group spread westward. The westward migration was periodic which is reflected in the presence of a number of facies intervals, which are bounded by unconformities or condensed intervals. Each unit represents a pulse of subsidence and subsequent sedimentation in the basin. Each interval onlaps argillaceous limestone, and has shifted westward with respect to the underlying unit. Each depositional interval records a deepening event. Stratigraphic work to date indicates that each overlying black shale unit is thinner than the previous one.

Units of the Utica have significant fracturing and abundant pyrite indicating deposition in anoxic conditions. The shale is sub-bituminous and “fresh samples can be ignited.” If a fresh sample is submerged in water, “an oily sheen rises to the water's surface.” Though data is sparse, TOC’s has been measured at over 3% by weight in New York, Ontario and Quebec. Analysis of cores show that the Utica thermally-mature with some mobile oil. Gas shows have been encountered in wells in eastern and central New York.

Current shale plays such as the Barnett and Antrim show that every shale play is somewhat unique, each with its own characteristics and problems. It is clear that the fractured Utica Group Shale offers the potential to be an economic natural gas play. More research is needed that addresses the geologic and reservoir properties of the shale.