Origins of Oil and Gas Sector Methane Emissions: On-Site Investigations of Aerial Measured Sources

• Published in: Environmental science & technology Vol. 57; no. 6; pp. 2484 - 2494
• Main Authors: Johnson, Matthew R., Tyner, David R., Conrad, Bradley M.
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 14.02.2023
• Subjects: Aerial surveys; Air Pollutants - analysis; British Columbia; Combustion; Compressors; Emission measurements; Emissions; Energy and Climate; Flares; Leak detection; Methane; Methane - analysis; Mitigation; Natural Gas - analysis; Oil and gas industry; Onsite; Pneumatics; Regulations; Surveys; Surveys and Questionnaires; Tanks; Vehicle Emissions - analysis; British Columbia; controlled storage tanks; uncontrolled storage tanks; compressors; methane venting; unlit flares; occurrence rates; population emission factors; combustion slip
• DOI: 10.1021/acs.est.2c07318
• ISSN: 0013-936X

Success in reducing oil and gas sector methane emissions is contingent on understanding the sources driving emissions, associated options for mitigation, and the effectiveness of regulations in achieving intended outcomes. This study combines high-resolution, high-sensitivity aerial survey data with subsequent on-site investigations of detected sources to examine these points. Measurements were performed in British Columbia, Canada, an active oil- and gas-producing province with modern methane regulations featuring mandatory three times per year leak detection and repair (LDAR) surveys at most facilities. Derived emission factors enabled by source attribution show that significant methane emissions persist under this regulatory framework, dominated by (i) combustion slip (compressor exhaust and also catalytic heaters, which are not covered in current regulations), (ii) intentional venting (uncontrolled tanks, vent stacks or intentionally unlit flares, and uncontrolled compressors), and (iii) unintentional venting (controlled tanks, unintentionally unlit/blown out flares, and abnormally operating pneumatics). Although the detailed analysis shows mitigation options exist for all sources, the importance of combustion slip and the persistently large methane contributions from controlled tanks and unlit flares demonstrate the limits of current LDAR programs and the critical need for additional monitoring and verification if regulations are to have the intended impacts, and reduction targets of 75% and greater are to be met.