Methane and the greenhouse-gas footprint of natural gas from shale formations

TLDR

Natural gas is largely methane, with 3.6%–7.9% of shale‑gas methane venting or leaking over a well’s lifetime, and methane’s global warming potential far exceeds that of CO₂, especially over the first few decades. We evaluate the greenhouse‑gas footprint of natural gas produced by high‑volume hydraulic fracturing from shale formations, focusing on methane emissions. Higher emissions arise during hydraulic fracturing—when methane escapes from flow‑back return fluids—and during drill‑out following fracturing. Methane emissions from shale gas are at least 30% higher—sometimes more than twice—than conventional gas, dominating the greenhouse‑gas footprint on a 20‑year horizon, making shale gas’s footprint greater than conventional gas or oil and at least 20% higher than coal over 20 years, though comparable over 100 years.

Abstract

We evaluate the greenhouse gas footprint of natural gas obtained by high-volume hydraulic fracturing from shale formations, focusing on methane emissions. Natural gas is composed largely of methane, and 3.6% to 7.9% of the methane from shale-gas production escapes to the atmosphere in venting and leaks over the life-time of a well. These methane emissions are at least 30% more than and perhaps more than twice as great as those from conventional gas. The higher emissions from shale gas occur at the time wells are hydraulically fractured—as methane escapes from flow-back return fluids—and during drill out following the fracturing. Methane is a powerful greenhouse gas, with a global warming potential that is far greater than that of carbon dioxide, particularly over the time horizon of the first few decades following emission. Methane contributes substantially to the greenhouse gas footprint of shale gas on shorter time scales, dominating it on a 20-year time horizon. 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. Compared to coal, the footprint of shale gas is at least 20% greater and perhaps more than twice as great on the 20-year horizon and is comparable when compared over 100 years.