Identification and characterization of high methane-emitting abandoned oil and gas wells

Mary Kang; Shanna Christian; Michael A. Celia; Denise L. Mauzerall; Markus Bill; Alana R. Miller; Yuheng Chen; Mark E. Conrad; Thomas H. Darrah; Robert B. Jackson

doi:10.1073/pnas.1605913113

New Research In

Edited by Steve W. Pacala, Princeton University, Princeton, NJ, and approved September 23, 2016 (received for review April 19, 2016)

This article has a Correction. Please see:

Correction for Kang et al., Identification and characterization of high methane-emitting abandoned oil and gas wells - July 10, 2017

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isotopes of methane; and noble gas concentrations from 88 wells in Pennsylvania with synthesized data from historical documents, field investigations, and state databases.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.

Footnotes

↵¹To whom correspondence should be addressed. Email: cm1kang{at}gmail.com.

Author contributions: M.K. designed research; M.K., S.C., M.A.C., D.L.M., M.B., A.R.M., Y.C., M.E.C., T.H.D., and R.B.J. performed research; M.K., S.C., M.B., and T.H.D. contributed new reagents/analytic tools; M.K., S.C., M.B., A.R.M., Y.C., and T.H.D. analyzed data; and M.K., S.C., M.A.C., D.L.M., M.B., Y.C., M.E.C., T.H.D., and R.B.J. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1605913113/-/DCSupplemental.

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