Studies: ‘Not Physically Plausible’ for HF to Pollute Water
2:02pm EST August 8, 2013
by Dana Bohandana@energyindepth.org, Washington, D.C.
Last year, Dr. Tom Myers released a report suggesting it was theoretically possible for hydraulic fracturing fluids to migrate vertically through thousands of feet of solid rock to contaminate water aquifers — within as little as three years’ time. As you might remember, the study, which was funded by the anti-fracking group Catskill Mountainkeeper, received a strong rebuke from the scientific community. As Energy In Depth has highlighted before, a report released in May from the Pennsylvania Geological Survey (PGS) and Pennsylvania Council of Professional Geologists (PCPG) found Dr. Myers’ assumptions were “unsupported by any empirical data,” among other problems. That same month, the research firm Gradient released a report analyzing potential exposure pathways for hydraulic fracturing fluids, including upward migration from the shale formation itself. According their report:
“[T]here is no scientific basis for significant upward migration of HF fluid or brine from tight target formations in sedimentary basins.”
Gradient recently published another paper, this one featured in the National Ground Water Association’s periodical Groundwater, which reiterates that Myers’ theory is basically impossible:
“Our review of the literature indicates that HF affects a very limited portion of the entire thickness of the overlying bedrock and therefore, is unable to create direct hydraulic communication between black shales and shallow aquifers via induced fractures. As a result, upward migration of HF fluid and brine is controlled by preexisting hydraulic gradients and bedrock permeability. We show that in cases where there is an upward gradient, permeability is low, upward flow rates are low, and mean travel times are long [often >1,000,000 years]. Consequently, the recently proposed rapid upward migration of brine and HF fluid, predicted to occur as a result of increased HF activity, does not appear to be physically plausible. Unrealistically high estimates of upward flow are the result of invalid assumptions about HF and the hydrogeology of sedimentary basins.” (p. 1)
“Our analysis and literature review indicate that where upward flow occurs, both permeability and flow rates are low, and therefore, timescales for transport are long. Overall, the rapid upward migration scenarios that have been recently suggested (Rozell and Reaven 2012; Myers 2012; Warner et al. 2012) are not physically plausible.” (p. 9)
As the authors point out, the geological characteristics of basins in which shale formations exist are not conducive to the upward migration of hydraulic fracturing fluids. For starters, the formations above these shales are typically of low permeability — including siltstones, mudstones, and shales. Secondly, hydraulic fracturing not only impacts a small portion of the rock, but the pressures associated with the process are “short lived and localized to the fracture network.”
A second peer-reviewed paper from Gradient, featured in the journal Geophysical Research Letters, echoed these findings. The study concluded:
“It is not physically plausible for induced fractures to create a hydraulic connection between deep black shale and other tight formations to overlying potable aquifers, based on the limited amount of height growth at depth and the rotation of the least principal stress to the vertical direction at shallow depths. Therefore, direct hydraulic communication between tight formations and shallow groundwater via induced fractures and faults (e.g., as suggested by Myers [2012], Rozell and Reaven [2012], and Warner et al. [2012]) is not a realistic expectation based on the limitations on fracture height growth and potential fault slip.” (p. 4)
These reports, completed with funding from Halliburton, are two more in a growing library of scientific literature that shows hydraulic fracturing does not pose a credible threat to groundwater resources. That fact has been reiterated by state and federal regulators, scientific experts, and industry engineers time and time again. So, while groups opposed to shale development hang on to the talking point that hydraulic fracturing is a threat to subsurface water supplies, the facts – and the studies — continue to prove them wrong.