Studying the Sources of Methane Migration Into Groundwater

Abstract

Methane Gas The rapid development of shale formations over the past decade has led the United States to become the world’s undisputed leader in natural gas production. This success, though, has come with increased scrutiny over the environmental impact of high-density drilling activities required to maintain unconventional gas production. One of the issues that industry and environmental experts are working to understand involves the risk of stray gas migration into groundwater sources, which a recent university study linked to cementing and casing failures. In their paper, researchers from Ohio State University, Duke University, Stanford University, and several other academic institutions, said the industry can do more to prevent this type of problem, ensuring that future onshore development poses as little risk as possible to people who live near oil and natural gas fields. However, there is scientific debate on such findings and whether natural sources of methane found in water sources are far more common. The early research by various organizations hopes to provide answers to questions such as the best way to sample residential water wells, how to distinguish naturally occurring methane from stray production gas, and what can be done to prevent well failures that might contaminate water. The Ohio State University-led study, produced by a team of Earth scientists, is one of the most comprehensive works on methane contamination to date and its findings were published in September by the Proceedings of the National Academy of Sciences, a 100-year-old, peer-reviewed scientific journal based in Washington, D.C. The study identified several potential ways methane can migrate into groundwater, and used noble gas analysis, which measures the isotopes of the gases that often accompany methane, to determine the most likely source. Although it has been used for other scientific purposes for decades, previous research has not used this method to link methane contamination to gas well failures. The report read, “In general, our data suggest that where fugitive gas contamination occurs, well integrity problems are most likely associated with casing or cementing issues.” The study involved taking samples from 113 water wells overlying the Marcellus Shale and 20 overlying the Barnett Shale during 2012 and 2013. One of its authors, Robert Jackson, a professor of Earth sciences at Stanford University, said higher-than-normal levels of methane were found in eight “clusters” of the sampled water wells, all located within 1 km of producing natural gas wells in Pennsylvania and Texas. “In the minority of cases where we found contamination, some of them were alarmingly high— well above saturation,” Jackson said. “They bubble like champagne when you pull the water out of the ground.” In the cases that were attributed to natural gas wells, Jackson said methane is either leaking out of the casing, or is coming from a shallower gas-bearing formation with insufficient cement isolation or an uncemented well section, thus allowing methane to flow up the annulus and into a shallow water-bearing layer.