Natural gas makes up about a quarter of the energy used in the United States.<ref>Ritter, K., Shires, T.M., Lev-On, M. 2015. Methane Emissions From Natural-Gas Systems: A Comparative Assessment for Select Industry Segments. SPE Economics & Management '''7'''(01): 22 - 28. SPE-168379-PA. http://dx.doi.org/10.2118/168379-PA. </ref> New production methods, including those related to hydraulic fracturing, are expanding access to natural gas and have increased natural gas based power, which is credited with decreasing greenhouse gas emissions in the country. Recent estimates for methane emissions from natural gas industries in the United States have been widely divergent. Some discrepancies noted by industry surveys have led to a thorough review of newly available information and are leading to the improvement of estimation methods and emission factors associated with activities that comprise natural-gas systems. This has manifested itself in the engineering estimations that are used for compiling the national GHG Emissions Inventory and in the methods used by companies for reporting under the mandatory national GHG Reporting Program. Both the inventory and the reporting program are programs of the US Environmental Protection Agency (EPA).
According to the EPA, about 29% of all methane emissions in 2012 came from oil and gas industry activity<ref name="r2">Rassenfoss, S. Pressure to Reduce Methane Emissions Highlights the Need for Better Monitoring. J Pet Tech '''67''' (3): 46-52. http://www.spe.org/jpt/article/8437-pressure-to-reduce-methane-emissions-highlights-the-need-for-better-monitoring.</ref>. E&P is the largest source of methane, followed by enteric fermentation--or the digestive process used by grazing animals, such as cattle, that produces methane as a gassy byproduct--at 25%. Grazing animals also produce manure, which is responsible for an added 9% of methane emitted.
With the direct measurements of emissions from devices on 377 wells operated by 10 companies cooperating on the survey, Dave Allen, a chemical engineer at the University of Texas, gathered data that reshaped the EPA’s estimates of E&P emissions of methane. Allen's study concluded that emissions during flowback have sharply decreased from 26% in the EPA’s Greenhouse Gas Inventory to 1%. The decline, combined with larger-than-expected emissions from gas-powered pneumatic control devices, pushed its share of natural gas emissions from the EPA estimate of 26% to 42%, making it the largest single category.
The EPA reports that nearly 29% of all methane emissions in 2012 came from oil and gas industry activity<ref name="r2"> Rassenfoss, S. Pressure to Reduce Methane Emissions Highlights the Need for Better Monitoring. J Pet Tech '''67''' (3): 46-52. http://www.spe.org/jpt/article/8437-pressure-to-reduce-methane-emissions-highlights-the-need-for-better-monitoring/. </ref>. It is the largest source, followed by enteric fermentation , at 25%, which is the digestive process used by grazing animals , such as cattle, producing methane as a gassy byproduct. Those animals also produce manure, which is responsible for an added 9% of methane emitted. Other estimates suggest far higher industry emission levels. That matters to the oil and gas business because those numbers will guide future emissions rule making.
Using direct measures of emissions from devices on 377 wells operated by 10 companies cooperating on the survey, Allen gathered data that reshaped the EPA’s pie chart of E&P emissions of methane. The study concluded that emissions during flowback have sharply dropped from 26% in the EPA’s Greenhouse Gas Inventory to 1%. That decline, plus larger-than-expected emissions by gas-powered pneumatic control devices, pushed its share of the natural gas emissions from the EPA estimate of 26% to 42%, making it the largest single category.
[[File:Wellsite emissions graph.jpg|frame|576x305px|Two 2015 studies of wellsite emissions showed a rapid drop in methane emissions from water flowing back after fracturing, increasing the relative importance of emissions by well equipment. (Rassenfoss) |link=http://petrowiki.org/File%3AWellsite_emissions_graph.jpg]]
== Reducing methane emissions ==
The EPA estimates that the industry’s natural gas emissions
are down by 16% since 1990. The largest gains over that period were from reduced emissions from control devices and installation of plunger lift systems. In recent years, some of the biggest gains have come from green well-completion methods , which capture gas that once escaped from fluids flowing back after fracturing. This is either flared or captured , processed , and sold to pipelines.
The EPA predicted that without further action by the industry and regulators, natural gas emissions would rise by 25% by 2025 as gas production rises. While the federal government is considering further action, some states have made moves. Colorado has become a proving ground for methane emission reduction methods , as well as research seeking better emission measurements.
What began as a deal to sharply reduce methane emissions negotiated among Colorado officials, three oil companies (Anadarko, Noble Energy, and Encana), and the EDF has led to a program to sharply reduce releases of methane and hydrocarbons that are ingredients in smog, known as volatile organic compounds (VOC).