The Environmental Protection Agency (EPA) has significantly revised downward its estimate for the past two decades of methane emissions from U.S. natural gas systems from the wellhead to the burnertip.

In a report released last week, the agency revised downward its estimates for methane emissions from natural gas systems for every year from 1990 through 2010. The largest revision was in the EPA’s estimate of methane emissions from gas systems in 2010. In its 2012 report, the EPA calculated that methane emissions from gas systems were 215.4 million metric tons of carbon dioxide (CO2) equivalent in 2010, but it cut the 2010 number by 33% to 143.6 million metric tons of CO2e in the report released last week.

“EPA’s 2012 report attempted to argue that methane emissions [from gas systems] had increased every single year from 1990 through 2009, with a slight decline in 2010. But revised data issued in 2013 demonstrate precisely the opposite: in fact, there has been a significant and consistent decline in total methane emissions since 1990. Last year’s report suggested an increase in methane emissions of 14% since 1990. EPA’s new data show a decline of 11%,” said the Indepdent Petroleum Association of America’s Energy In Depth.

The Natural Gas Council (NGC) commended EPA for the improvement in its data collection.

“Through coordination with the natural gas industry, EPA incorporated more accurate data in its 2013 inventory, using data that was more recent and represented more wells. As a result, the agency revised its estimated methane emissions rate for the natural gas value chain downward…Further reductions are expected when additional data becomes available as a result of EPA’s Subpart W greenhouse gas reporting requirement,” said Ron Jibson, chairman of NGC and the American Gas Association, and chairman of Questar Corp.

“The Natural Gas Council is pleased that EPA is getting closer to reality regarding emissions rates as opposed to continuing to use the unsupported numbers included in last year’s Inventory.

“There are efforts underway in every segment of the industry to continue to reduce emissions and improve the overall impact of natural gas on the environment, including ‘green’ well completions and upgrading transmission and delivery infrastructure. But we must have accurate and fact-based data that reflects those improvements so that we can truly understand the impact of our energy usage and make smart decisions about our nation’s energy future,” he said.

EPA said the lower methane emissions were due to a decline in emissions from transmission and storage, and a fall-off in distribution emissions due to the trend away from using cast iron and unprotected steel to build pipelines. The emissions from field production fell 12% from 1990 through 2011, the EPA reported.

In a report issued last June, the American Petroleum Institute (API) and America’s Natural Gas Alliance (ANGA) locked horns with the EPA over its calculations for methane emissions from unconventional wells using hydraulic fracturing. Based on a survey of 91,000 gas wells operated by more than 20 companies, compared to the EPA’s survey of 8,880 wells in 2010, the report by ANGA and the API estimated that methane emissions in the field from gas wells were 4.42 million metric tons, significantly below the 8.79 million metric tons that the EPA had calculated (see NGI, June 11, 2012). The API-ANGA report focused on only one segment of the industry — hydraulic fracturing — whereas the EPA’s latest emission numbers apply to all gas systems.

Overall greenhouse gas (GHG) emissions, which include methane emissions, have decreased slightly in the United States, thanks primarily to natural gas, according to the EPA report. The agency said GHG emissions in the nation fell 1.6% from 2010 to 2011. The decrease was mainly driven by power plants switching from coal to natural gas. Overall, GHG emissions in 2011 declined 6.9% since 2005. But longer term emissions in the United States have risen by 8.4% since 1990.

Power plants still are the single biggest source of GHG emissions, emitting 33%. Electricity emissions have risen by about 18% since 1990. Transportation accounted for 28% of the emissions in 2011; industry accounted for 20%; commercial and residential, 11%; and agriculture, 8%, the EPA said.

Total emissions of the six main greenhouse gases in 2011 were equivalent to 6,702 million metric tons of CO2. The gases include CO2, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride.

President Obama has pledged to reduce U.S. GHG emissions 17% below 2005 levels by 2020, The Hill newspaper said. Despite the general decline in GHG emissions, many experts contend that the administration will have to take further steps to meet the 2020 goal.

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