Natural gas is much cleaner than coal but it's also important that its energy return on investment (EROI) - the total input energy with the energy expected to be made available to end users - is similar to coal, according to a paper in the Journal of Industrial Ecology.
The paper looked at gas from horizontal, hydraulically fractured wells in the Marcellus Shale of Pennsylvania and their analysis indicates that the EROI ratio of a typical well is likely between 64:1 and 112:1, with a mean of approximately 85:1. This range assumes an estimated ultimate recovery of 3.0 billion cubic feet per well, similar to the estimated ultimate recovery of coal, which falls between 50:1 and 85:1.
Environmentally, natural gas is the cleanest fossil fuel. It produces much lower quantities of nitrogen oxides and carbon dioxide - half as much carbon dioxide, less than a third as much nitrogen oxides, and one percent as much sulfur oxides - than burning coal or oil for energy does.
"Our analysis indicates that gas can be extracted from shale efficiently, from an energy perspective. The energy return on (energy) investment ratio (EROI) does seem to be at least as favorable as coal," said lead author Mike Aucott. "However, a comparison with coal is difficult. There appear to be large amounts of coal still available. Estimates of the amount of gas available from the shale plays vary widely. It is not clear yet whether there is anywhere near enough to rival coal over the long haul."
"There are concerns about water pollution and other environmental impacts associated with shale gas production. With the assumption that these can be managed, and that production quantities remain consistent with initial production data, the favorable EROI suggests that shale gas will be a viable energy source for quite some time."
Citation: Michael L. Aucott and Jacqueline M. Melillo, 'A Preliminary Energy Return on Investment Analysis of Natural Gas from the Marcellus Shale', Journal of Industrial Ecology Article first published online: 17 JUN 2013 DOI: 10.1111/jiec.12040