The US Environmental Protection Agency "grossly" overstated the amount of methane being emitted into the atmosphere from hydraulically fractured shale gas wells and those emissions should be completely reevaluated in light of better data and industry practices, a new IHS CERA report said Wednesday.
"Emissions are not being measured," said report co-author and IHS CERA Director of North American Natural Gas Mary Barcella. "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."
EPA and others are concerned about methane emissions because methane is has 25 times the impact on greenhouse gases as carbon dioxide, and the emissions are thought to be on the rise with the growth in the number of gas wells drilled into US shale plays.
But the IHS CERA report says the EPA's basic 2010 estimate is founded on only four data points and is an incorrect assumption.
EPA's estimates stem from data collected from four "green" completions that measured the amount of methane the driller captured after fracking the well and hooking it to a pipeline for sale. EPA then assumed that the amount of methane captured in the green completions would be equal to the amount of methane that wasn't captured by other types of completion.
Operators using "green" completion techniques use surge vessels, tanks and separators, as well as rapid connection to a gathering line, to reduce the amount of gas emitted to the atmosphere after flowback fluids are purged from a fracked well.
IHS CERA said that assuming all the gas from wells that were not completed "green" winds up in the atmosphere is a fundamental error that ignores the need for drillers to be safe and capture the value of gas coming from the well.
"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," said IHS CERA Director and report co-author Surya Rajan. "Gas that cannot be sold is generally flared rather than vented for safety reasons. 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."
Beginning with the use of data from only four projects in Wyoming, New Mexico, Texas and Oklahoma, the EPA compounds its overestimation of methane emission by assuming all US gas wells emit the average of the four points, which themselves have initial production rates that vary between 700 Mcf/d to 20,000/Mcf/d for a nationwide average IP rate of 9,175 Mcf/d, IHS CERA said.
"Finally, EPA assumed that flaring did not take place is it was not required and that pure methane was vented to the atmosphere," the report said, an assumption that goes against the industry's practice to flare wells, instead of venting them, a safety measure to prevent the build-up of hazardous methane levels around a well pad.
The EPA's estimate of methane emission doesn't pass any test of reasonableness, the report said.
IHS CERA calculated that 10.7 Bcf/d, or 18%, of the 58.2 Bcf/d of US natural gas produced in 2010 came from new wells.
"Even if each well had vented all its eventual daily production during a 10-day flowback period, the total methane emitted during flowback [completion] procedures in 2010 would have been 107 Bcf," the report said. That represents 43 million tons of carbon dioxide equivalent, the report said, two-thirds less than the EPA's 2009 estimate of 130 mtCO2e emitted from gas wells. "This is a gross overestimate," the report said.
The study concluded that recently proposed EPA performance standards for the gas industry under the Clean Air Act -- which do not target methane, but are designed to reduce emissions of sulfur dioxide and volatile organic chemicals -- will help the EPA gather better data for policymaking going forward.
"The proposed standards have the potential to codify good operating practice in the gas drilling industry," the report said. "The data collection requirement could also provide much more reliable data on methane emissions from gas well completions, a potential benefit to all who seek to better understand GHG emissions from the industry."
