[Image above] New research suggests that, despite fears to the contrary, the residual treatment water used in hydraulic fracturing poses no serious risk to surrounding supplies of water. But does that mean fracking is safe? Not so fast, says a team of environmental scientists. Credit: Daniel Foster; Flickr; CC BY-NC-SA 2.0
As scientists actively explore new solutions to an old problem (i.e., what to do with the groundwater produced by hydraulic fracturing), research out of Penn State University suggests that, despite fears to the contrary, the water poses no serious risk to surrounding supplies of water.
According to a PSU news release, the research team—comprised of Terry Engelder, professor of geosciences at Penn State, Lawrence Cathles, professor of earth and atmospheric sciences at Cornell University, and Taras Bryndzia, geologist at Shell International Exploration and Production Inc.—found that residual treatment water (RTW) injected into shale during fracking remains sequestered in the rock formation due to “multiphase capillary phenomena.” As a result, contamination of ground water is “not likely.”
“Capillary forces and coupled diffusion–osmosis processes are the reasons the brines and the RTW are not free to escape from gas shale,” says Engelder in the release. “The most direct evidence of these forces is the observation that more than half the treatment waters are not recovered. Introducing treatment water causes gas shale to act like a sponge based on the principles of imbibition.”
Thanks to high capillary suction, the shale wicks water in and pushes natural gas out, keeping the RTW in place in what Engelder calls a “permeability jail” for more than 200 million years.
“If one wants to dispose of fracking waters, one could probably not choose a safer way to do so than to inject them into a gas shale,” he says.
To test the imbibition and sequestration capabilities, the research team experimented on parts of Pennsylvania’s Marcellus gas shale and the Haynesville gas shale in northwest Louisiana.
“The hydraulic fracturing fluid consists mostly of very low-salinity surface water, while the shale contains high concentrations of water soluble inorganic cations and anions,” Engelder says. “During hydraulic fracturing, water is lost to the formation while inorganic cations and anions are transferred from the formation to the hydraulic fracture. Diffusion osmosis assists the rapid imbibition of water by the shale and diffusion of ions into the treatment water, causing the high salinities observed in flowback fluids. The point to be emphasized here is that this osmotic pressure pushes the hydraulic fracture fluids into the shale matrix, expelling gas and cations to make high-salinity flowback in the process.”
Recent work from Ohio State University assistant professor Thomas Darrah echoes the findings of the sequestration study, attributing contamination not to the actual act of fracking, but to leaky wells that bring gas to the surface. (Click here to read more, or here to access the paper appearing in PNAS.)
But a study published in the Annual Review of Environment and Resources finds that—whether from the fracking process or a drippy pipeline—though the waters rarely reach supplies of drinking water, fracking is not without environmental impacts.
The known-to-fail steel and cement casings—which have a failure rate between 1 percent and 10 percent—closer to the surface and the disposal of wastewater are the real problems, say the paper’s authors, seven environmentalists from Duke, MIT, Ohio State, Stanford, Newscastle University, Los Alamos National Lab, and the National Oceanic and Atmospheric Administration.
Injecting the wastewater deep below the earth’s surface, which has been known to cause seismic activity, could become a more attractive recycling solution “if energy companies follow basic guidelines and undertake careful monitoring.”
The authors have outlined policies and practices to “optimize” the environmental cost-benefit balance of fracking, but they say further research is needed.
“Almost no comprehensive research has been done on health effects, but decisions about drilling—both approvals and bans on fracking—are made all the time based on assumptions about health risks,” says Robert Jackson, environmental scientist at Stanford and one of the paper’s authors.
Meanwhile, fracking—and the debate that surrounds it—continues.
The RTW sequestration findings, supported by the Research Partnership to Secure Energy for America and Penn State’s Appalachian Basin Black Shale Energy Group, are titled “The fate of residual treatment water in gas shale” (DOI: 10.1016/j.juogr.2014.03.002) and published in the Journal of Unconventional Oil and Gas Resources.
The environmental impact paper is “The environmental costs and benefits of fracking” (DOI: 10.1146/annurev-environ-031113-144051).
For some additional reading, see the January 2014 ACerS Bulletin, which provided an in-depth look at fracking and opportunities for ceramic science to make a difference. (Access to the Bulletin archives are a members-only benefit. To join—for access to this and other exclusive membership benefits—click here.)