In the NETL study a hydraulically fractured shale gas well was injected with four different man-made tracers at different stages of the fracking process. The preliminary results did not find any of the tracers above the 5,000 foot depth. This study is important because it adds to our knowledge of the impact of fracturing on geology, but geology varies across the Marcellus shale formation and from shale formation to formation so these results may apply only to this section of the Marcellus shale formation. In addition, the wells at the research site are likely to have been completed “by the book.”
How a well is completed may be one of the most important determinates if there will be any shallow impact from hydraulic fracturing, or fracking as it is more commonly known. When a well is fracked fluids made up of mostly water and chemical additives are injected at high pressure into a geologic formation. The pressure used exceeds the rock strength and the fluid opens or enlarges fractures in the rock. As the formation is fractured, a “propping agent,” such as sand or ceramic beads, is pumped into the fractures to keep them from closing as the pumping pressure is released. The fracturing fluids (water and chemical additives) are partially recovered and returned to the surface or deep well injected in some geologies. Natural gas will flow from pores and fractures in the rock into the wells allowing for enhanced access to the methane reserve. The NETL study is also performing seismic monitoring to understand the fracturing process and how naturally occurring fractures are impacted by fracking.
As has been shown by research performed at other locations and by Duke University and other researchers, how carefully a well is completed and the surrounding geology determines the potential for fracking to impact groundwater. In the study in Northeast Pennsylvania the Duke scientists found that natural gas, derived both naturally and at least in part from the shale gas was present in some of the shallow groundwater wells less than a mile away from natural gas wells. Dr. Rob Jackson the lead author pointed out that the two simplest explanations for the higher dissolved gas concentrations measured in the drinking water were faulty or inadequate steel casings and/or imperfections in the cement sealing (also known as the grouting) between casings and rock that keep fluids from moving up the outside of the well. In 2010, the Pennsylvania Department of Environmental Protection (DEP) issued 90 violations for faulty casing and cementing on 64 Marcellus shale gas wells; 119 violations were issued in 2011.
In another study by Duke University and the US Geological Survey no evidence of drinking water contamination from methane from shale gas was found in a part of the Fayetteville Shale in Arkansas (2). That shale has a less fractured geology than the Marcellus and good confining layers above and below the drinking water aquifers.
In Wyoming where the water table is deep and the shale gas shallow the drinking water has been impacted, but the cause of the impact is still under investigation. The Environmental Protection Agency, EPA, reported in 2011 that they found glycols, alcohols, methane and benzene in a well drilled to the water aquifer in Wyoming within the Pavillion field. Initially EPA reported that the contaminants found were consistent with gas production and hydraulic fracturing fluids and likely due to fracking, but has since backed off that conclusion stating “the source of those contaminants has not been determined.” EPA now states that their efforts to evaluate potential migration pathways from deeper gas production zones to shallower domestic water wells in the Pavillion gas field are inconclusive. EPA has turned the investigation over to the Wyoming Department of Environmental Quality and the Wyoming Oil and Gas Conservation Commission who will assess the need for any further action to protect drinking water resources.
EPA does not plan to finalize or seek peer review of its draft Pavillion groundwater report released in December, 2011. Nor does the agency plan to rely upon the conclusions in the draft report and is backing away from a report that initially claimed to show fracking contaminated groundwater. EPA is moving forward on a major research program on the relationship between hydraulic fracturing and drinking water in different areas of the country and will release a draft report in late 2014. EPA will look to the results of that national program as the basis for its scientific conclusions and recommendations on hydraulic fracturing.
Meanwhile the NETL preliminary results are all over the news as the final word instead of simply another piece of knowledge in a recent slew of studies. Ultimately, we need to understand why, in some cases, shale gas extraction appears to contaminate groundwater and how to ensure that contamination does not happen with a high level of certainty in susceptible geology. Well construction and maintenance needs to be studied, optimized and carefully regulated before further expansion of shale gas development.
1. Jackson, RB, Vengosh, A, Darrah, TH, Warner, NR, Down, A, Poreda, RJ, Osborn, SG, Zhao, K, Karr, JD (2013) Increased stray gas abundance in a subset of drinking water wells near Marcellus shale gas extraction PNAS 2013 ; published ahead of print June 24, 2013, doi:10.1073/pnas.1221635110
2. Kresse TM, et al. (2012) Shallow Groundwater Quality and Geochemistry in the Fayetteville Shale Gas-Production Area, North-Central Arkansas, 2011 (USGS), US Geological Survey Scientific Report 2012–5273 (Lafayette Publishing Service Center, Lafayette, LA).
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