Geochemical Exploration for Trenton-Black River Gas Reservoirs In New York and Ohio

Seneshen, David M., Viellenave, James H., and Fontana, John V.

Direct Geochemical, Golden, CO

The innovative application of both organic and inorganic surface geochemical tools facilitates Trenton-Black River gas exploration and structural mapping in the Appalachian Basin. Concentrations of tightly adsorbed hydrocarbons in the fine fraction of soils are determined by thermal desorption and Flame-Ionization Detector Gas Chromatography (FID-GC). Major and trace element concentrations in the same fine fraction of soils are estimated by aqua regia acid digestion and analysis of the supernatant for 26 elements by Inductively Coupled Emission Spectroscopy (ICP-ES).

The interrelationship of C1-C6 hydrocarbons in soils is used to discriminate between  “gas-prone” and “dry” areas. Discriminant analysis of C1-C6 hydrocarbon data reveals that the most important variables for distinguishing between these areas are, in order of importance, ethylene, isobutane, isopentane, methane and propane. Soils over the gas fields are characterized by anomalous C1/C2 ratios and light alkenes (i.e. ethylene and propylene), which is not surprising considering the dry gas composition of these hydrothermal dolomite reservoirs (i.e. >98% methane). A “Mississippi Valley Type” element association, which includes calcium, magnesium, strontium, zinc, and lead, is prevalent in soils over faults that crosscut or parallel gas reservoirs. Soils over the faults also show anomalous alkane/alkene ratios. The results of geochemical surveys over shallow reservoirs in Ohio (1,400-1,500 feet) and deep reservoirs in New York (9,000-10,000 feet) will be presented to emphasize the value of these geochemical tools for exploration risk reduction and structural mapping.