The National Science Foundation (NSF) said Monday that scientists have developed new geochemical tracers that can identify hydraulic fracturing (fracking) flowback fluids that have been spilled or released into the environment.
The tracers have been field-tested at a spill site in West Virginia and downstream from an oil and gas brine wastewater treatment plant in Pennsylvania.
"By characterizing the isotopic and geochemical fingerprints of enriched boron and lithium in flowback water from hydraulic fracturing, we can now track the presence of 'frack' fluids in the environment and distinguish them from wastewater coming from other sources, including conventional oil and gas wells," said Duke University geochemist Avner Vengosh, who co-led the research.
"This gives us new forensic tools to detect if frack fluids are escaping into our water supply and what risks, if any, they might pose."
The researchers published their findings Monday in the journal Environmental Science & Technology. The study, which was funded by NSF, is the first to report on the development of the boron and lithium tracers.
"With increasing exploitation of unconventional oil and gas reservoirs through the use of hydraulic fracturing, it's important that we are able to assess the extent of hydraulic fracturing fluids entering the environment," said Alex Isern, section head in NSF's division of earth sciences.
"This work is critical as it demonstrates that geochemical fingerprinting provides a powerful tool to differentiate potential sources of contamination and therefore guide efforts to mitigate environmental impacts."
Adds Nathaniel Warner of Dartmouth College, lead author of the paper, "This new technology can be combined with other methods to identify specific instances of accidental releases to surface waters in areas of unconventional drilling.
"It could benefit industry as well as federal and state agencies charged with monitoring water quality and protecting the environment."
It is possible to identify the presence of frack fluid in spilled or discharged flowback by tracing synthetic organic compounds that are added to the fluid before it's injected down a well, Vengosh said, but the proprietary nature of these chemicals, combined with their instability in the environment, limits the usefulness of such tracers. By contrast, the new boron and lithium tracers remain stable in the environment. "The difference is that we are using tracers based on elements that occur naturally in shale formations," Vengosh said.
When drillers inject frack fluids into a shale formation, they not only release hydrocarbon, but also boron and lithium that are attached to clay minerals in the formation. As the fluids react and mix at depth, they become enriched in boron and lithium. As they're brought back to the surface, they have distinctive fingerprints that are different from other types of wastewater, including wastewater from a conventional gas or oil well, and from naturally occurring background water, the researchers said.