Credit: Avner Vengosh
“Deep-well injection is the preferable disposal method, but injecting large volumes of wastewater into deep wells can cause earthquakes in sensitive areas and is not geologically available in some states.
“In Pennsylvania, much of the flowback is now recycled and reused, but a significant amount of it is still discharged into local streams or rivers.”
It’s 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.
“This type of forensic research allows us to clearly identify possible sources of wastewater contamination,” Vengosh said.
Thomas Darrah of The Ohio State University, Robert Jackson of Duke and Stanford Universities and Romain Millot and Wolfram Kloppmann of the French Geological Survey also co-authored the paper, which was partly funded by the Park Foundation.
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