Guest Blogger: New Study Indicates Gas from Cows is the Largest Contributor to Methane Emissions (Not Shale/Unconventional Natural Gas Production)

US EPA Assumptions vs. Actual Data:

Collection and analysis of actual activity data by API (as opposed to US EPA’s assumptions) related to liquids unloading and venting and refracture rates for unconventional wells dramatically reduced the overall methane emissions from Natural Gas Systems.  For example applying emission factors based on recent API data reduced the methane emissions from liquids unload and venting by 86% (from 4.5 million metric tons to 637,766 metric tons.   These reductions were largely due to lower percentages of: wells having plunger lifts, wells venting to the atmosphere and well vent times.  Similarly, data collected by API regarding refracture rates associated with unconventional wells ranged 0.7% to 2.3%, significantly lower than US EPA’s 10% refracture rate assumption.  Using the revised refracture rate reduced the methane emission estimate for this source by 72% (from 712,605 metric tons to 197,311 metric tons).

Emission Estimation Complexity, Public Confidence, and the Industry’s Future:

API’s study demonstrates the complexity associated with estimating emissions from natural gas production because of diversity of operations (due to geologic and other factors), the lack of a single coordinated source of well completions, well counts, and associated data as well as lack of emissions data (including small sample size) for various pieces of equipment associated with gas production including centrifugal compressors and pneumatic controls.  That said, the API, points out that with respect to the sector’s emissions, the industry is currently taking steps to enhance the emissions estimation, transparency, and public confidence.  These steps include the following:

The Industry will be reporting its emissions for the first time in the fall of 2012 pursuant to the requirements under 40 CFR Part 98 Subpart W Mandatory Greenhouse Gas Report for Petroleum and Natural Gas Systems that went into effect on January 1, 2011.  API believes that over time, the data will be more complete and accurate and will allow for better estimates of key emission source categories;

The industry is committed to continuous improvement for upgrading equipment and/or altering its practices to reduce emissions and other environmental impacts.  With respect to emissions, the industry knows that “things that get measured can be used to enhance performance” particularly when it is in the industry’s self-interest to reduce the tension between environmental, economic, and operational considerations;

Last but not least, these steps, with continued industry efforts to work with the US EPA and other stakeholders will promote the accurate and defensible use of emission data by all.