Some environmentalists have argued that high levels of methane leaks and emissions make natural gas a poor alternative to coal for generating electricity. However, total greenhouse gas (GHG) emissions – carbon dioxide, methane, nitrogen oxides and some fluorinated gases – have declined as natural gas has replaced coal in power generation. However, atmospheric methane continues to rise and the scientific evidence is unclear on whether oil and gas operations are the source of the increase. These emissions analyses take on added importance because the Obama administration is rushing to enact additional oil and gas industry regulations to help meet the President’s Climate Action Plan (CAP) goal of reducing methane emissions by 40 to 45 percent below 2012 levels by 2025.
State of Emissions
The White House recently reported, “U.S. carbon dioxide emissions from the energy sector fell by 9.5 percent from 2008-15, and in the first 6 months of 2016, they were at the lowest level in 25 years.” The Council of Economic Advisers credited the shift to natural gas for 66 percent of the carbon emissions reduction, while increased generation from zero-carbon renewable energy provided 34 percent of the reduction.
In addition, Energy Secretary Ernest Moniz recently reaffirmed his support for hydraulic fracturing, saying the natural gas boom has been good for the environment, “displacing high-carbon coal with natural gas producing fewer emissions.”
Looking just at anthropogenic methane, sources include domestic animals (including manure management), the oil and gas industry, landfills, rice cultivation, wastewater, coal mining and biomass. Wetlands are the dominant natural methane source. However, geologic sources – thermogenic and biogenic methane produced in the Earth’s crust and released into the atmosphere from land and submarine faults and seeps – may be significant although they have not been comprehensively measured.
Global atmospheric methane concentrations increased during most of the 20th century, excluding the period from 1999 to 2006, when atmospheric levels stayed level. Methane levels have increased since 2006, and the 2015 level was about 1800 parts per billion – up from about 1700 ppb in 1988. The major concern is that there is not a scientific consensus on the cause of the renewed increases.
To state the obvious, mitigating fugitive emissions requires knowing where or what they come from. However, identifying the source is difficult. In many oil and gas-producing areas, potential sources may include livestock, coal mines or waste treatment facilities. An additional complication is that methane detection has been conducted using a hand-held or vehicle mounted detector or sampler at a small number of facilities. Airborne sampling — primarily done with National Oceanic and Atmospheric Administration airplanes — captures methane from all sources and must also be corrected for wind and weather conditions.
A recent American Chemical Society report by David Allen details one of the major problems impacting methane emission estimates: “estimates based on source sampling extrapolated to regional or national scale (‘bottom-up analyses’) differing from estimates that infer emissions based on ambient data (‘top-down analyses’) by 50 percent or more.”
Here are some of the recent studies on possible causes of the recent increases in atmospheric methane:
- A September report in the Proceedings of the National Academy of Sciences by Andrew Rice and others uses isotopic studies to find that “methane emissions from the fossil fuel sectors were approximately constant in the 1980s and 1990s but increased significantly between 2000 and 2009.”
- A recent study by atmospheric scientists in New Zealand, Germany and the United States (Schaefer et al., 2016) found that increases in atmospheric methane were not caused by fossil fuel production, but more likely from wetlands or agriculture.
- Another recent study from the Royal Holloway, University of London (Nisbet et al., 2016) found that the increase in atmospheric methane from 2007 to 2013 was dominated by significant increases in biogenic methane emissions, especially from wetlands, ruminants and rice paddies in the tropics.
- Amy Townsend-Small presented data at the 2016 Eastern Section AAPG Meeting that showed that “despite active natural gas extraction in Denver, at least 50 percent of methane emissions in these regions are from agricultural and/or landfill sources. Previous studies had attributed most or all emissions of methane to natural gas production.” Townsend-Small also reported on a study where pre-drill water samples showed that biogenic methane is the primary component of dissolved methane in groundwater wells in the Utica Shale area.
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Even as disagreements about the sources and amounts of fugitive methane continue, oil and gas operators have to monitor their facilities and repair leaks based on rules in several states. In addition, the Environmental Protection Agency (EPA) now requires monitoring and leak repair at new oil and gas facilities including wells, compressors, pumps and transmission lines.
Starting in October, EPA began to collect large volumes of information about oil and gas industry operations, facilities and emissions to help them formulate rules for fugitive methane monitoring and mitigation from existing facilities.