A study from the University of Texas at Austin studied 190 onshore natural gas sites and concluded that well completion activities in hydraulically fractured wells emitted 97% less methane than the EPA's 2011 national emission estimates, which were released in April 2013. The EPA estimated that 81 Mg of methane was emitted per completion flowback, while the study found that on average 1.7 Mg of methane was emitted per completion flowback studied. While the well completion activities were found to emit less methane, the study found that total methane emissions from natural gas production was comparable to the most recent EPA estimates. The study further stated this disparity could be explained by emissions detected from the pneumatic controllers and equipment leaks, which the study found had emitted at least 30% more methane than the EPA estimates indicated.
The study noted a potential flaw, which is that several of the samples included in the study were small and should be examined with caution when extrapolating the results to larger populations.
The study may be found at: http://www.pnas.org/content/early/2013/09/10/1304880110.full.pdf+html