Borehole Characterization of Deep Groundwater in Selected Hydrogeologic Settings of the Marcellus Shale Play

Deep groundwaters in selected hydrogeologic settings of the Marcellus shale play were characterized through borehole logging and sampling. The characterized boreholes and their hydrogeologic setting were: 1) three stratigraphic test holes on upland ridges underlain by lower Pennsylvanian, Mississippian, and upper Devonian bedrock; 2) a frac-water supply test well in an upland headwater valley underlain by lower Pennsylvanian, Mississippian, and upper Devonian bedrock; 3) a domestic water-supply well in a tributary stream valley underlain by till and upper Devonian bedrock; and 3) a geothermal wellfield in a major river valley underlain by stratified drift and upper Devonian bedrock The methods used to characterize the deep- groundwater zones penetrated by the boreholes included core and cuttings analysis; petrophysical logging; televiewer and video imaging; fluid-property and flow logging; and open-hole and discrete-zone hydraulic testing and water-quality sampling.

Sparse fractures below depths of 250 meters on the upland ridges and 100 meters in the upland headwater valley produced very small flows of saline water. In the river valley, a laterally extensive fractured zone at a depth of 80 meters produced large flows of saline water. The saline waters in the upland and valley settings were characterized as diluted brines and contained elevated methane of early thermogenic origin. Fractured zones at depths of 200 meters on the upland ridges, 85 meters in the upland headwater valley, and 50 meters in the tributary valley had transitional water quality and lower hydraulic head than the freshwater zones above and saline-water zones below. In the river valley, the fractured top of bedrock at a depth of 45 meters produced freshwater and had lower hydraulic head than the saline-water zones below.