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  U.S. Lab Suggests Shale Fractures Unlikely to Threaten Water Supply      


June 18, 2012
"Reprinted with permission. Copyright 2012 E&E Publishing, LLC."
Hydraulic fracturing is unlikely to pose a threat to drinking water aquifers, according to preliminary results from a government-led study in the Marcellus Shale natural gas formation in Pennsylvania.
The study adds to the back-and-forth on a fundamental question that plagues residents: Does the process of hydraulic fracturing lead to the formation of large cracks through which fracking fluid and methane can migrate into groundwater aquifers?
Most research has suggested not. The geology of the Earth varies so much, from shale, to sandstone, to other types of rock that each new layer acts like a natural barrier, one study found (EnergyWire, April 27).
Another recent study acknowledged the improbability of the event, then placed a time scale on the unlikely migration of about a century (EnergyWire, May 4).
Initial results of the latest work, from the National Energy Technology Laboratory (NETL), confirm that cracks formed by fracking are typically not long enough to connect the Marcellus to aquifers. The longest fractures scientists have found so far extend only 1,500 feet above the shale, well below any potential water aquifers. This matches with industry results.
NETL scientists took an extra step to confirm there had been no contamination. They injected separate chemicals with the fracking fluid so that, if there is any upward migration of the fluids or gas, the additional chemicals will end up closer to the surface. NETL scientists will spend a year keeping an eye out for signs that those chemicals migrated.
"Chances are, if there is communication, we might be able to see that very quickly, but if there's no communication, which we kind of expect, we are going to have to monitor for a fairly long length of time to ensure that is indeed the case," said Richard Hammack, geologist at NETL.
The research is ongoing, and final results will be published next year.
NETL is working at a site in Greene County, Pa., in collaboration with a company that is fracking 8,000 feet into the Marcellus Shale basin. There is a second natural-gas-rich formation 4,000 feet above the site called the Upper Devonian, where a company is extracting gas. There is no water aquifer at the site, which is ideal for the scientists' work. The Upper Devonian gas wells act like a proxy for aquifers, and the research can be conducted without any worries about contaminating water supplies.
The scientists will watch for the appearance of the chemical tracers in the gas and produced water of the Upper Devonian wells.
"It is an ideal underground real-world lab to investigate hydraulic fracturing, the propagations of these induced fractures, and also the possible migration, or not, of gases and liquids between two deep zones," Hammack said.
The larger goal of the study is to get a better technical understanding of what happens during the hydraulic fracturing event. This can help form models of the migration of fluids underground that can be used at other sites where companies are fracking.
"What we are trying to do is build confidence by collecting data on baseline signals in the environment, by documenting what happens during fracture propagation, using a variety of methods to be able to document where fluids go and don't go during the process," said George Guthrie, head of geological and environmental systems at NETL.
NETL scientists said previous research and industry data suggest it's unlikely contamination will be found.
"We have good reason to believe things like fracturing can be done in a way that is normally contained within the zone, and that is based on modeling, based on phases that can serve as barriers to propagation of fractures. It is based on industry information that has come out," Guthrie said.
"Reprinted with permission. Copyright 2012 E&E Publishing, LLC."
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