Conducted as part of the National Energy Technology Laboratory research for the Department of Energy, a new study has encouraging findings regarding the impact of hydraulic fracturing. The study, conducted during hydraulic fracturing of wells in southwestern Pennsylvania, found no detectable migration of gas or aqueous fluids, and that the impact of hydraulic fracturing on the rock mass did not extend to the Upper Devonian/Lower Mississippian gas field during or after hydraulic fracturing.
Titled “An Evaluation of Fracture Growth and Gas/Fluid Migration as Horizontal Marcellus Shale Gas Wells are Hydraulically Fractured in Greene County, Pennsylvania” the study was funded from oil and gas royalties directed to the Department of Energy under provisions of the Energy Policy Act. Teams with members from industry, government, and academia performed the work. The teams included members from the National Energy Technology Laboratory, West Virginia University, and the University of Pittsburgh. The work was completed as part of research for the Department of Energy’s Complementary Research Program.
The study found no detectable migration of gas or aqueous fluids.
Fluid and Gas Migration
Sampling to detect possible migration of fluid and gas from the underlying hydraulically fractured wells began two months before the hydraulic fracturing to establish background levels. Gas samples were collected and analyzed up to 8 months after the fracturing, and produced water samples were collected and analyzed up to 5 months after the activity. Production/pressure histories and tracer analysis were used to monitor for potential gas or fluid migration. The study reported that no detectable migration of gas or fluids occurred during the monitoring period.
Using microseismic monitoring, the study also set out to determine the maximum height of fractures created by the hydraulic fracturing activity. The impact of hydraulic fracturing on the rock mass did not extend to the Upper Devonian/Lower Mississippian gas field: Although microseismic events were observed higher than would be expected based on the assumption that the Tully Limestone is an upper frac barrier, the uppermost microseismic events were at least 1,800 ft below the lowermost producing zone in the Upper Devonian/Lower Mississippian gas field.
Numerous microseismic events were observed above the Tully Limestone layer, thought to be an upper barrier to fracture growth from hydraulic fracturing in the Marcellus Shale. According to the researchers, those microseismic event clusters suggested that energy from hydraulic fracturing was focused along pre-existing joints, low-offset faults, and bedding planes.
The study can be found here.
The suggested citation for the study is: Hammack, R.; Harbert, W.; Sharma, S.; Stewart, B.; Capo, R.; Wall, A.; Wells, A.; Diehl, R.; Blaushild, D.; Sams, J.; Veloski, G. An Evaluation of Fracture Growth and Gas/Fluid Migration as Horizontal Marcellus Shale Gas Wells are Hydraulically Fractured in Greene County, Pennsylvania; NETL-TRS-3-2014; EPAct Technical Report Series; U.S. Department of Energy, National Energy Technology Laboratory: Pittsburgh, PA, 2014; p 76.