REPORT Gas well integrity and methane migration: evaluation of published evidence during shale-gas development in the USA Patrick A. Hammond 1 & Tao Wen 2 & Susan L. Brantley 2 & Terry Engelder 3 Received: 14 August 2019 /Accepted: 11 January 2020 # The Author(s) 2020 Abstract More than 1 million wells may have been completed using hydraulic fracturing techniques in the USA alone; however, there have been few case studies exploring the impacts on water resources due to methane migration. This study evaluated the results of three investigations initiated by the US Environmental Protection Agency, that were subsequently described in published studies at Dimock in Pennsylvania, Parker-Hood County in Texas, and Pavillion in Wyoming, as well as another study completed at Sugar Run in northeast Pennsylvania. In addition, earlier investigations at Shaws Corner in Pennsylvania, Jackson County in West Virginia, Garfield County in Colorado, and Bainbridge in Ohio are summarized. The most common cause of incidents was the presence of uncemented sections of production casings in wells that allowed gas migration from intermediate depths to shallow freshwater aquifers. In three cases, an inadequate depth of the primary top of cement (TOC) also contributed to impacts. Sources of methane were best identified through analyses of isotopes on samples from production casings, annular spaces, and water wells. In Dimock, some isotope signatures changed with time, after the completion of remedial actions. In Parker-Hood County, where impacts were not related to gas well activity, noble gas analyses were also needed to determine the source of gas. At Pavillion, where maximum methane concentrations in water wells were <1 mg/L, no significant impacts were documented. For all the sites, most or all of the fugitive gas incidents may have been prevented by fully cementing production casings to the land surface. Keywords Stable isotopes . USA . Hydraulic fracturing . Methane migration . Well integrity Introduction Migration of stray methane gas has been at the center of the debate on the impacts caused by shale gas drilling and hydrau- lic fracturing activities on the quality of shallow drinking wa- ter resources. While not a regulated contaminant, methane can accumulate to explosive levels and cause asphyxiation in con- fined spaces, as well as initiate adverse chemical reactions such as the reduction of iron and manganese compounds in well water (Gorody 2012; Woda et al. 2018). In the late 1940’s, hydraulic fracturing was developed to increase pro- duction from conventional oil and gas wells. By 2002 in the Barnett Shale in Texas, USA, wells in unconventional reser- voirs such as low-permeability shale were being developed using horizontal drilling and high volume hydraulic fracturing (HVHF). HVHF procedures are also used for production of hydrocarbons from other “tight” formations (sandstones, silt- stones, and carbonates) and coalbeds. The US Environmental Protection Agency (US EPA 2016) reports that more than 300,000 wells may have been completed using HVHF tech- niques since 2000, about half in the state of Texas. The primary way to protect drinking water resources from gas migration during development of gas wells is to effective- ly cement the well casings. A typical gas well consists of conductor, surface and, sometimes, intermediate casings. After cementing each casing, a production casing is extended Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10040-020-02116-y) contains supplementary material, which is available to authorized users. * Patrick A. Hammond patrick.hammond@maryland.gov; phammond@broadstripe.net 1 Maryland Department of the Environment, 1800 Washington Blvd, Baltimore, MD 21230, USA 2 Earth and Environmental Systems Institute, Pennsylvania State University, 2217 EES Building, University Park, PA 16802, USA 3 Pennsylvania State University, 443 Deike Building, University Park, PA 16802, USA Hydrogeology Journal https://doi.org/10.1007/s10040-020-02116-y