The Proceedings of the National Academy of Sciences recently published a study of direct measurements of methane emissions from sources at 190 onshore natural gas production sites using operational practices. The estimate of total emissions from this study is similar to the Environmental Protection Agency’s (EPA) recent National Emissions Inventory of methane emissions from natural gas production.

However, the results of this study also demonstrated that methane emissions from new wells being made ready for continuous production captured 99% of methane emissions for the wells using methane capture or control measures. This is a substantial decrease in the EPA’s national inventory estimates from 2011. As reported by the study, the emissions measured from completion flowbacks during the study are about 600 Gg lower than the completion flowback emissions in the current EPA National Emissions Inventory.

The process of completion, which is the process of preparing a well for continuous production, is thought to be a major source of methane leaks at hydraulic fracturing sites. However, the results of the study regarding completion indicate that practices of combusting or capturing emissions from completion flowbacks lead to a reduction of methane emissions. These practices will be required by EPA regulations starting in January 2015, although some companies are already capturing escaping gases during the completion process.

Previous analyses of greenhouse gas emissions have been based on engineering estimates of emissions or measurements made downwind of well sites. This is the first comprehensive study of direct measurements of methane emissions at natural gas production sites throughout the United States.

The study was conducted by the University of Texas and was funded by the Environmental Defense Fund and nine petroleum companies. 

Co-authored by Michael N. Mills and Rebecca C. Guiao.