The furor over fracking took a further twist this week as levels of the greenhouse gas methane were found above drilling wells, in some cases, 1,000 times greater than previous Environmental Protection Agency estimates.
The shocking figures came from air samples taken above shale gas wells drilled the Marcellus Shale Formation in Pennsylvania at production points not previously believed to be an important emissions source.
The findings, contained in a study led jointly by Purdue and Cornell universities, will certainly have implications for the evaluation of the environmental impact of natural gas production.
The concern arises due to the potency of methane as a greenhouse gas. Methane is the main constituent of natural gas making up about 95 percent of a product that energy companies are increasingly “mining” through the process of hydraulic fracture — fracking — of shale deposits.
Previous EPA studies have put emissions from gas wells as low as between 0.04 and 0.30 grams of methane per second but the new study recorded atmospheric methane at some locations between 100 to 1,000 times higher than official EPA figures, with levels closer to 34 grams of methane per second at a some Pennsylvania drill sites.
When methane is used as a fuel, as well as producing energy, it breaks down to water and carbon dioxide, another greenhouse gas. But it’s not a like-for-like trade. Although burning methane itself is a major contributor to atmospheric carbon dioxide levels, free methane in Earth’s atmosphere is reckoned to be 20 times more efficient than CO2 at trapping the sun’s heat in the Earth’s atmosphere, according to the US Environmental Protection Agency.
Hence a number of past studies expressing grave concern over what will happen if massive methane deposits, currently locked up in frozen permafrost regions, begin to thaw.
The new research from Purdue and Cornell universities, published this week in the Proceedings of the National Academy of Sciences, was one of a few to take a top-down approach measuring levels of methane gas in the atmosphere above wells. It identified seven individual well-pads with high emission levels and categorized how these emission points slotted in, in the shale-gas development process.
The wells with the highest emissions accounted for less than 1 percent of the total number of wells in the area surveyed but all the wells emitting high methane levels were found to be in the drilling stage. Significantly, that pre-production stage was not previously associated with high levels of methane emissions.
Commenting on the team’s findings, Paul Shepson, professor of Chemistry and Earth Atmospheric and Planetary Sciences at Purdue who co-led the study with Jed Sparks, professor of Ecology and Evolutionary Biology at Cornell, said, “These findings present a possible weakness in the current methods to inventory methane emissions and the top-down approach clearly represents an important complementary method that could be added to better define the impacts of shale gas development."
And on the relatively small number of wells contributing to high methane levels, Shepson had this to say, “This small fraction of the total number of wells was contributing a much larger large portion of the total emissions in the area, and the emissions for this stage were not represented in the current inventories."
In other words, the highly potent greenhouse gas, methane, has been leeching into the atmosphere from wells not thought previously to be a source.
To conduct their well-head survey, researchers flew above part of the Marcellus Shale Formation in south-western Pennsylvania in Purdue University’s Airborne Laboratory for Atmospheric Research, a specialist aircraft used for scientific surveys.
The Marcellus Shale Formation covers a huge area extending from the Canadian border, taking in the Allegheny Plateau region of the northern Appalachian Basin. Within Marcellus, shale deposits have been found in New York State, New Jersey, Pennsylvania, Ohio, Maryland, Virginia and West Virginia. Currently, most drilling operations for natural gas are in the western portion of Virginia.
The aerial survey let researchers identify plumes of methane gas from single well-pads, groups of well-pads and larger regional scales and to examine the production state of the wells.
"It’s particularly noteworthy that large emissions were measured for wells in the drilling phase, in some cases 100 to 1,000 times greater than the inventory estimates," Shepson noted, continuing, "This indicates that there are processes occurring - e.g., emissions from coal seams during the drilling process - that are not captured in the inventory development process. This is another example pointing to the idea that a large fraction of the total emissions is coming from a small fraction of shale gas production components that are in an anomalous condition."
The methodology adopted to date by the EPA to measure methane emissions from fracking operations is to compile the energy industry’s own measurements of emissions at well sites, according to Climate Central.
The EPA then extrapolates these numbers to produce an estimate of total methane emissions over a given area. The new study, however, highlights how not actually measuring methane emissions may contribute to a distorted picture.
The problem could be significant since the EPA"s most recent greenhouse gas inventories record natural gas production and distribution as being second only to livestock as the biggest single source of atmospheric methane, reports Climate Central.
Shepson described the existing assessment criteria as bottom-up inventories produced from industry measurements of emissions from distinct production, transmission and distribution components. These are then scaled up to create an estimate of emissions for a region. But with thousands of wells, coupled with a complex processing and transmission system associated with each shale basin, Shepson said obtaining a representative data set is difficult.
Meanwhile, Tuesday, as part of the Obama administration’s Strategy to Reduce Methane Emissions (PDF), the EPA published a series of technical white papers on sources of methane emissions in the energy sector. The white papers detail five major sources of sources of methane emissions across the hydrocarbon industry, comprising compressors, emissions from completions and ongoing production of hydraulically fractured oil wells, leaks, liquids unloading and pneumatic devices.
The EPA says it will use the papers, along with input received from peer reviewers and the public, “to determine how to best pursue additional reductions from these sources.”
A period of public consultation remains open until June 16, 2014.
In the light of the Purdue-Cornell study, one might reasonably anticipate more than a few members of the public recommending the EPA actually measures methane leakage on site, rather than place too much reliance on energy industry estimates.
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