Southeastern Section - 67th Annual Meeting - 2018

Paper No. 3-5
Presentation Time: 9:30 AM


ZHU, Junfeng1, PARRIS, T. Marty1, TAYLOR, Charles J.1, WEBB, Steven E.1, DAVIDSON, Bart1, SMATH, Richard A.1, RICHARDSON, Stephen D.2, MOLOFSKY, Lisa J.3, SMITH, Ann P.2 and KROMANN, Jenna S.2, (1)Kentucky Geological Survey, University of Kentucky, 228 Mining and Mineral Resources Building, Lexington, KY 40506, (2)GSI Environmental Inc, 9600 Great Hills Trail, Suite 350E, Austin, TX 78759, (3)GSI Environmental Inc., 2211 Norfolk St. Suite 1000, Houston, TX 77098

In eastern Kentucky, horizontal drilling and hydraulic fracturing are being used to develop and evaluate unconventional reservoirs in the Devonian Berea Sandstone and the Cambrian Rogersville Shale in recent years. With more than 100 wells drilled, the Berea play is being developed at a small scale with shallow fracturing depths of less than 600 m. The Rogersville play is in its early stages, but has the potential to become a major shale gas play with large-scale hydraulic fracturing at depths of 2,000 m to more than 4,000 m. Development of these unconventional reservoirs has prompted concerns about potential impacts to groundwater resources in the region.

In 2016, we sampled 51 water wells to provide a first assessment of dissolved methane in groundwater overlying the Berea and Rogersville plays. Our data showed that methane was detected in 78 percent of the sampled wells (40 of 51 wells) and about half of the wells (26 of 51 wells) had methane concentrations above 1 mg/L. The highest methane concentration was 78 mg/L. Higher methane concentrations were found associated with sodium-rich water and reducing redox conditions. No correlation was found between methane concentrations and distances between sampled wells and nearest vertical oil and gas wells. The 26 wells with methane concentrations greater than 1 mg/L were also analyzed for stable carbon and hydrogen isotopic composition of methane (δ13C-CH4 and δ2H- CH4). The isotopic composition of δ13C-CH4 (-84.0‰ to -58.3‰) and δ2H-CH4 (-246.5‰ to -146.0‰), along with a dominance of dry gas in most wells (21 of 26 wells), indicated that dissolved methane was primarily formed with microbial origin through CO2 reduction pathway. However, two wells with a biogenic signature based on isotope data also showed a possible thermogenic influence, as indicated from the occurrence of ethane and propane.