Estimates that the US Environmental Protection Agency and others have used for greenhouse gas (GHG) emissions from shale gas production probably are overstated, IHS Cambridge Energy Research Associates said in a new report. The estimates are based on assumptions that do not reflect current industry practices and should be reevaluated, the Aug. 24 report concluded.
“Methane emissions have become a very important and controversial issue given their potency as a greenhouse gas,” said Mary Barcella, IHS CERA director of North American natural gas. “Unfortunately, such emissions are not being measured. Estimates are being used that are not supported by data, do not reflect current industry practice, and would be unreliable to use as a base for decision-making.”
The report cited EPA’s 2010 revised estimates of methane emissions during well completion as one example. It said EPA’s current methane emissions estimate methodology during this phase was based on a small sample of wells and primarily measured methane that was captured instead of released into the atmosphere.
EPA estimates were based on two workshop presentations describing methane captured during “green completions”—operations designed to capture as much methane as possible, according to the report. It said EPA assumed that similar methane levels were produced at every other US well, and that those emissions were not captured at all. Such assumptions do not conform to current industry practices, it stated.
“The assumption that all methane recovered from these sample wells would otherwise have been flared or vented is questionable at best, given that common industry practice is to capture gas for sale as soon as it is technically feasible,” IHS CERA director Surya Rajan said.
Excess gas flared
“Gas that cannot be sold is generally flared rather than vented for safety reasons,” Rajan said, adding, “If the methane emissions at wells were as high as some methodologies assume, you would have extremely hazardous conditions at the well site that neither regulators nor industry would permit.”
The report said another key mischaracterization found in EPA’s estimates and other recent reports, such as a study led by Cornell University Prof. Robert W. Howarth, is the assumption that wells in flowback contain methane in quantities equal to their post-completion daily production. The assumption results in a significant overestimation of methane emissions, it indicated.
The IHS CERA report noted that data on unconventional gas well GHG emissions are currently lacking due to the fact that they are not adequately measured. More reliable data are needed in order to produce estimates with any degree of certainty, it suggested, adding that this might be the most productive result of additional regulations which EPA proposed in July.
Some of the other proposed regulations, such as requiring green completions and flaring of any produced gas that is not suitable for sale, are already common natural gas production industry practices, it said.
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