Assessing Methane in Shallow Groundwater in Unconventional Oil and Gas Play Areas, Eastern Kentucky

Authors: J. Zhu, T. Parris, C. Taylor, S. Webb, B. Davidson, R. Smath, S. Richardson, L. Molofsky, J. Kromann, A. Smith
Published: August 2017 in Ground Water.

Abstract

The expanding use of horizontal drilling and hydraulic fracturing technology to produce oil and gas from tight rock formations
has increased public concern about potential impacts on the environment, especially on shallow drinking water aquifers. In eastern
Kentucky, horizontal drilling and hydraulic fracturing have been used to develop the Berea Sandstone and the Rogersville Shale. To
assess baseline groundwater chemistry and evaluate methane detected in groundwater overlying the Berea and Rogersville plays,
we sampled 51 water wells and analyzed the samples for concentrations of major cations and anions, metals, dissolved methane,
and other light hydrocarbon gases. In addition, the stable carbon and hydrogen isotopic composition of methane (δ13C-CH4 and
δ2H-CH4) was analyzed for samples with methane concentration exceeding 1 mg/L. Our study indicates that methane is a relatively
common constituent in shallow groundwater in eastern Kentucky, where methane was detected in 78% of the sampled wells (40 of
51 wells) with 51% of wells (26 of 51 wells) exhibiting methane concentrations above 1 mg/L. The δ13C-CH4 and δ2H-CH4 ranged
from −84.0‰ to −58.3‰ and from −246.5‰ to −146.0‰, respectively. Isotopic analysis indicated that dissolved methane was
primarily microbial in origin formed through CO2 reduction pathway. Results from this study provide a first assessment of methane
in the shallow aquifers in the Berea and Rogersville play areas and can be used as a reference to evaluate potential impacts of future
horizontal drilling and hydraulic fracturing activities on groundwater quality in the region.