Natural gas energy is suitable for the mitigation of global climate change and can serve as a good transition step on the road towards greater use of low-carbon energy sources. In a recent paper published in the journal "Geochemistry, Geophysics and Geosystems", L. M. Cathles finds "substitution of natural gas [for coal and some oil] reduces global warming by 40% of that which could be attained by the substitution of zero carbon energy sources."

He also states, "the policy implications of this analysis are: (1) reduce the leakage of natural gas from production to consumption so that it is ~1% of production, (2) encourage the rapid substitution of natural gas for coal and oil, and (3) encourage as rapid a conversion to low carbon sources of energy as possible."

Discussing gas leakage

Natural gas burns much "cleaner" than coal and oil, but gas leakage during production and transportation may counteract the greenhouse gas emission benefits of natural gas. For this reason gas leakage rates, especially from unconventional gas wells, are discussed in the aforementioned article. Based on recent data (Harrison, 2012) on gas leakage during completion of shale gas and tight-sand wells, provided by the industry to the U.S. Environmental Protection Agency (EPA), the author concludes that "leakage is ~0.01% [of production] and similar to that from conventional gas well completions and workovers".

This leakage rate is much lower than previously published data suggest, and benefits from the fact that 93.5% of the 1578 unconventional gas wells covered by the recent industry data "were green completed, that is, they were connected to a pipeline in the pre-initial production stage, so there was no need for them to be either vented or flared."

These data show that green completions indeed have the potential to significantly reduce gas leakage from unconventional wells. Green completions will be compulsory in the U.S. from 2015 onwards.

Greenhouse gas emissions from the natural gas industry, especially from unconventional wells, are also currently being discussed by other sources. The U.S. EPA has revised its calculation methodology for Natural Gas Systems, substantially increasing their estimated greenhouse gas emissions for the production sector of Natural Gas Systems (EPA 2010, EPA 2011).

These numbers were criticized in a consultancy report (IHS CERA 2011) and, more recently, in a report from the American Petroleum Institute (API) and America’s Natural Gas Alliance (ANGA). The data from the latter industry survey, which relies on a much larger database than the U.S. EPA, result in significantly lower emission estimates for liquids unloading and unconventional gas well refracturing, when compared with the EPA’s emission estimates in the national inventory.