Unexpectedly High Methane Concentrations over Shale Gas Fields

by Emil Morhardt

Methane, the main constituent of natural gas (both that from gas wells and from farm operations) is a powerful greenhouse gas, around 30 times more potent than CO2 over the hundred years after it is emitted. It is on the rise, and the culprit might be shale gas development, which utilizes hydraulic fracturing (fracking). Caulton et al. (2014) used an airplane to sample the air above a 2,800-square-kilometer area of the Marcellus shale formation gas fields in Pennsylvania. It was rich in methane, with between 2 and 15 grams heading skyward over each square kilometer every second, the upper limit of which is quite a lot higher than the 5 grams estimated from what was previously known about wellhead methane emissions; the authors suspected that the transient nature of gas leakage might be the reason, making very difficult to come up with an average over time from ground-level measurements. Since they were in an airplane, however, they could circle around areas of high concentrations and pinpoint the source. It turns out that…

 sure enough, the sources were well pads and, in one case, a coal mine, but the interesting thing is that these wells were in an early state of development, hadn’t reached their full depth, and hadn’t yet been fracked (hydraulically fractured). The large releases at this stage of development were completely unexpected, but the culprit pads were visibly missing commonly used approaches that might have prevented the releases (shale shakers, mud pits), so it may have been carelessness on the part of the drillers causing the releases.

Similarly high measurements have been obtained from flights over well fields in Texas, Oklahoma, and Kansas, suggesting a widespread national problem. At this stage it doesn’t look like the problem is fracking, so much as failure to employ standard techniques to capture the methane and save it or flare it, but clearly something needs to be done.

Caulton, D.R., Shepson, P.B., Santoro, R.L., Sparks, J.P., Howarth, R.W., Ingraffea, A.R., Cambaliza, M.O., Sweeney, C., Karion, A., Davis, K.J., 2014. Toward a better understanding and quantification of methane emissions from shale gas development. Proceedings of the National Academy of Sciences 111, 6237-6242. http://bit.ly/1qOe8Yx

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