ABSTRACT

Recent technological advances in horizontal drilling and high-volume hydraulic fracturing have made the Marcellus Shale the newest gas-development target or play in the northern Appalachian basin. Protection of freshwater aquifers from contamination by saltwater and gas during the development of the Marcellus Shale play is an issue of concern. Chemung, Tioga, and Broome Counties are in the southwestern part of the Marcellus Shale play in New York and likely will be the focus of drilling early in development of the play in the State. As a preliminary step in understanding and protecting the groundwater resource in the three-county area, logs of water wells in the U.S. Geological Survey National Water Information System and gas wells in the New York State Museum Empire State Oil and Gas Information System were evaluated for the determination of the presence of freshwater, saltwater, and gas above the Marcellus Shale.

Results of the evaluation of the water- and gas-well logs indicate that freshwater aquifer zones are log normally distributed with depth in the three-county study area and that freshwater circulates to a greater depth in the uplands than in the valleys. The base of the freshwater aquifer appears to be about 800 feet below land surface in upland settings but only about 200 feet below land surface in valley settings. At depths greater than 200 feet in valley settings, groundwater in the Upper Devonian bedrock, and in a few areas in the glacial drift, is salty. Gas is present locally in the glacial drift, Upper Devonian bedrock, Tully Limestone, and Hamilton Group above the Marcellus Shale. The highest rates of gas flow above the Marcellus Shale may be associated with the Tully Limestone. The frequency of gas zones generally increases with depth in the Upper Devonian bedrock with pockets of gas locally present above the base of the freshwater aquifer.

Consistent and complete reporting of freshwater, saltwater, and gas during the drilling of future Marcellus shale-gas wells would greatly improve existing information. Field measurement of specific conductance of water produced during drilling and specific-conductance and temperature wireline geophysical logging of open boreholes prior to surface-casing installation would enhance the value of the gas-well logs. Compilation and integration of information from water wells that are inventoried and sampled for water quality during gas development with data from ongoing county-wide and regional programs would provide an important database for understanding and protecting the freshwater aquifers.

First posted February 4, 2011