Abstract
We evaluate the greenhouse gas footprint of natural gas obtained by highvolumehydraulic fracturing from shale formations, focusing on methane emissions.Natural gas is composed largely of methane, and3.6% to 7.9% of the methane fromshale-gas production escapes to the atmosphere in venting and leaks over the lifetimeof a well. These methane emissions are at least 30% more than and perhapsmore than twice as great as those from conventional gas. The higher emissions fromshale gas occur at the time wells are hydraulically fractured—as methane escapesfrom flow-back return fluids—and during drill out following the fracturing. Methaneis a powerful greenhouse gas, with a global warming potential that is far greaterthan that of carbon dioxide, particularly over the time horizon of the first fewdecades following emission. Methane contributes substantially to the greenhousegas footprint of shale gas on shorter time scales, dominating it on a 20-year timehorizon. The footprint for shale gas is greater than that for conventional gas or oil
when viewed on any time horizon, but particularly so over 20 years.