The linked reference indicates that there are more abandoned well than previously believe that may (or are) leak methane gas; while the following linked article indicates that most likely Donald J. Trump will likely gut Obama's tighter regulations to control such methane leaks from wells:
Mary Kang, et. al. (2016), "Identification and characterization of high methane-emitting abandoned oil and gas wells", PNAS, doi: 10.1073/pnas.1605913113http://www.pnas.org/content/early/2016/11/08/1605913113
Significance: "Millions of abandoned oil and gas wells exist across the United States and around the world. Our study analyzes historical and new field datasets to quantify the number of abandoned wells in Pennsylvania, individual and cumulative methane emissions, and the attributes that help explain these emissions. We show that (i) methane emissions from abandoned wells persist over multiple years and likely decades, (ii) high emitters appear to be unplugged gas wells and plugged/vented gas wells, as required in coal areas, and (iii) the number of abandoned wells may be as high as 750,000 in Pennsylvania alone. Knowing the attributes of high emitters will lead to cost-effective mitigation strategies that target high methane-emitting wells."
Abstract: "Recent measurements of methane emissions from abandoned oil/gas wells show that these wells can be a substantial source of methane to the atmosphere, particularly from a small proportion of high-emitting wells. However, identifying high emitters remains a challenge. We couple 163 well measurements of methane flow rates; ethane, propane, and n-butane concentrations; isotopes of methane; and noble gas concentrations from 88 wells in Pennsylvania with synthesized data from historical documents, field investigations, and state databases. Using our databases, we (i) improve estimates of the number of abandoned wells in Pennsylvania; (ii) characterize key attributes that accompany high emitters, including depth, type, plugging status, and coal area designation; and (iii) estimate attribute-specific and overall methane emissions from abandoned wells. High emitters are best predicted as unplugged gas wells and plugged/vented gas wells in coal areas and appear to be unrelated to the presence of underground natural gas storage areas or unconventional oil/gas production. Repeat measurements over 2 years show that flow rates of high emitters are sustained through time. Our attribute-based methane emission data and our comprehensive estimate of 470,000–750,000 abandoned wells in Pennsylvania result in estimated state-wide emissions of 0.04–0.07 Mt (1012 g) CH4 per year. This estimate represents 5–8% of annual anthropogenic methane emissions in Pennsylvania. Our methodology combining new field measurements with data mining of previously unavailable well attributes and numbers of wells can be used to improve methane emission estimates and prioritize cost-effective mitigation strategies for Pennsylvania and beyond."
See the relevant article on Trump likely walking-back Obama's tighter methane emission regulations:https://www.washingtonpost.com/news/energy-environment/wp/2016/11/11/this-is-the-other-way-that-trump-could-worsen-global-warming/?utm_term=.668fcd59cef1
Extract: "… Trump is also expected to seek to reverse or undermine another set of Obama policies meant to curb climate change that focus not on carbon dioxide, the most notorious greenhouse gas, but rather methane …
… Obama’s 45 percent reduction target for methane emissions by 2025 now appears unlikely to happen, says Stanford’s Jackson …"