Study monitors a hydraulic fracturing operation in Greene County, Pa.
The U.S. Department of Energy’s National Energy Technology Laboratory (NETL) has released a technical report on the results of a limited field study that monitored a hydraulic fracturing operation in Greene County, Pa., for upward fracture growth out of the target zone and upward gas and fluid migration. Results indicate that under the conditions of this study, for this specific location, fracture growth ceased more than 5,000 ft below drinking water aquifers and there was no detectable upward migration of gas or fluids from the hydraulically fractured Marcellus Shale.
Hydraulic fracturing is a method used to improve gas and oil production from low permeability formations (shale and tight sand reservoirs). During this process, large volumes of sand and water, with small volumes of chemical additives, are injected into low-permeability subsurface formations. The injection pressure of the fluid creates fractures that increase oil and gas flow, while the sand holds the fractures open.
The research study, led by NETL’s Office of Research and Development, used natural and manmade tracers to look for evidence that fluid and gas in this area from the hydraulically fractured Marcellus Shale had migrated at least 3,800 ft upward to a gas-producing zone of Upper Devonian/Lower Mississippian-age shale, midway between the Marcellus Shale and the surface. Microseismic monitoring from geophone arrays placed in two vertical Marcellus Shale gas wells were used to determine the upper extent of induced fractures.
During hydraulic fracturing at the Greene County site, researchers detected microseismic signals using downhole geophones. All signals recorded were at least 2,000 ft beneath the Upper Devonian/Lower Mississippian gas field, and more than 5,000 ft below drinking water aquifers. Gas samples from the Upper Devonian/Lower Mississippian gas field were collected two months prior to hydraulic fracturing, and up to eight months afterward, and no evidence of gas migration was detected. Monitoring of the Upper Devonian gas field up to five months following fracturing produced no evidence of fluid migration.
This research was funded through oil and gas royalties from drilling on federal lands legislatively directed to the Department of Energy under provisions of the Energy Policy Act of 2005, Complementary Program. The work was conducted via collaboration between government, industry and academia, in order to provide an unbiased, science-based source of information with which future decisions about shale gas development may be guided.