Houston (Platts)--28Nov2012/509 pm EST/2209 GMT

A new study by MIT researchers finds the actual amount of methane emissions caused by production of natural gas in shale formations has been greatly exaggerated in previous studies, particularly a controversial Cornell University study released last year. The MIT researchers found that the potential methane emissions per well in the Barnett and Haynesville shales were 273 metric tons and 1,177 metric tons, respectively. However, when the researchers took into account actual gas handling practices in the field, they found that actual emissions were reduced to about 35 mt of methane per well from an average Barnett well and 151 mt from an average Haynesville well. This compares with potential emissions of 252 mt of methane emissions per well in the Barnett and 4,638 mt per well in the Haynesville, reported in the study by a team of Cornell University researchers led by Robert Howarth. The peer-reviewed MIT study, released this week in the journal "Environmental Research Letters," reviewed emissions data from about 4,000 wells drilled in the five most prolific US gas shale basins in 2010. "The issue is that nobody knows the real number," in gauging the volumes of so-called fugitive methane emissions released from shale gas wells in the US, Sergey Paltsev, the study's co-author, said in an interview Wednesday. Paltsev, the assistant director for economic research at the MIT Joint Program on the Science and Policy of Global Change, said the methane emissions recorded by the MIT study are also lower than estimates reported by the US Environmental Protection Agency, which is phasing in rules to reduce fugitive emissions from gas wells and midstream gas sites. However, when compared with the Cornell study, the EPA's "numbers are much closer to ours," Paltsev said. In a technical support document attached to EPA's greenhouse gas reporting rules in 2010, the agency, which measures emissions in cubic feet rather than metric tons, estimated the average emissions at 9,175 Mcf per well. The MIT study is just the latest scientific paper to challenge the conclusions of Howarth's study, which claimed that the greenhouse gas footprint of shale gas was larger than that of conventional gas, oil, and, over a 20-year time frame, coal. Methane, the main ingredient of natural gas, is a far more potent greenhouse gas than CO2. In August, the Department of Energy said in a report that the global warming potential of fugitive methane released during the life cycle of gas from extraction to combustion is half that of coal as measured over both 20-year and 100-year periods. Howarth's study has been used by opponents of shale gas drilling to challenge the environmental benefits of the practice. "His conclusions that shale gas is worse than coal made a lot of headlines. Several researchers are trying to challenge their findings," Paltsev said. He added that the EPA's attempt to reduce emissions across the entire gas value chain is "a movement in the right direction." By focusing his attention solely on emissions from shale gas wells, Howarth's study had found "the wrong place to put the blame," Paltsev said. Instead, emissions occur across the entire gas train, from the well head -- of both conventional and unconventional gas wells -- to the burner tip. "There is nothing about unconventional shale gas that is changing that," he said. --Jim Magill, jim_magill@platts.com --Edited by Carla Bass, carla_bass@platts.com