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Assessment of Methane Emissions from Oil and Gas Production Pads using Mobile Measurements
Citation:
Brantley, H., E. Thoma, B. Squier, B. Guven, AND D. Lyon. Assessment of Methane Emissions from Oil and Gas Production Pads using Mobile Measurements. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 48(24):14508-14515, (2014).
Impact/Purpose:
This paper summarized EPA mobile measurements of methane emissions from oil and gas production pads from 2010-2013 using draft inspectio method OTM 33A. Results are compared to other studies. This paper is a collaboration output under the MOU with EDF signed 7/13/13 (attached). This paper will be part of a synthesis study being compiled by EDF. Paper Summary: "In summary, the OTM 33A mobile inspection method was successfully applied to quantify CH4 emissions at 218 oil and gas well pads with an accuracy of ± 60 % determined by tracer release tests. Well pad emissions were log-normally distributed and differed significantly by basin with geometric means ranging from 0.14 g/s in the Denver-Julesburg to 0.57 g/s in the Pinedale basin. Repeat measurements at 11 sites indicated consistent low emission rates at eight sites but highly variable emissions at three sites. The production rates accounted for approximately 9 % of the variation in emission rate in a multivariate linear regression. While emission rates in g/s were comparable with published on-site direct measurement studies, emissions as a percentage of production were higher by a factor of 7 or more, indicating that sites with lower production levels often emit a much greater percentage of production. Infrared camera videos indicate that emission rates may be strongly affected by stochastic variables. In particular, equipment malfunctions or operator error may cause emission rates to increase substantially compared to normal operating conditions. Accurately estimating site emissions on a regional scale likely will require determining the average frequency of these stochastic events.
Description:
Journal Article Abstract --- "A mobile source inspection approach called OTM 33A was used to quantify short-term methane emission rates from 218 oil and gas production pads in Texas, Colorado, and Wyoming from 2010 to 2013. The emission rates were log-normally distributed with geometric means of 0.32, 0.14, and 0.57 g/s in the Barnett, Denver-Julesburg, and Pinedale basins, respectively. Although the current study focused on sites with emision rates above 0.01 g/s, overall distributions were similar to those observed in recent onsite direct measurement studies. Repeat OTM 33A measurements in the Pinedale basin found eight sites with consistently low emissions and three sites with larger, variable emission rates. One source was identified by infrared camera as an open thief hatch of a condensate tank. Considering data across all basins, a multivariate linear regression was used to assess the relationship of methane emissions to well age, gas production, and oil or condensate production. Methane emissions were correlated with gas production but only approximately 9 % of the variation in emission rates was explained by variation in production levels. OTM 33A emissions as a percent of gas production were approximately an order of magnitude higher than other recent direct measurement studies. This observation is explained by the site selection criteria for the OTM 33A inspection studies (no low emitting sites studied) coupled with measurement of elevated short-term emissions (i.e., condensate tank flashing) and maintenance-related emissions not fully reflected in previous on-site studies. Sites with low production were found to emit disproportionately higher methane as a percentage of production, indicating that maintenance-related stochastic variables and production/control equipment design level are factors determining emissions."
