Natural gas obtained from shale formations using the controversial method of hydraulic fracturing (“hydrofracking”) have a higher greenhouse gas footprint than when obtained from conventional methods, according to a study recently released by the academic journal Climate Change Letters.

The preliminary peer-reviewed study also found that in a 20-year time frame, shale gas extracted through the hydrofracking process emits more greenhouse gas than coal.  Over the past several years hydrofracking has significantly increased in the U.S. as energy companies seek to extract gas from the Barnett, Fayetteville, Haynesville and Marcellus shales.

Companies such as Haliburton, Cabot Oil and Gas Co. and Southwestern Energy Co. have all been named in lawsuits alleging the companies contaminated water around the operations or harmed nearby residents with toxic fumes from their hydrofracking wells.

Natural gas is mostly composed of methane, a greenhouse gas. The study reported approximately 3.6 percent to 7.9 percent of methane from shale gas is released and escapes into the atmosphere over the lifetime of a hydrofracking well.  In comparison, about 1.7 percent to 6 percent of methane emissions from conventional gas extraction is released, the study reported.

The study was the first look at the total greenhouse gas footprint of natural gas obtained from shale formations, said Tony Ingraffia of Cornell University, speaking to Law 360, one of the study’s three authors. The report used data from the U.S. Environmental Protection Agency and the U.S. General Accountability Office.

Mr. Ingraffia said the data was incomplete and, in some cases, highly inaccurate.  “We’re hoping that the paper will stimulate the industry or other researchers to make more accurate measurements,” said Mr. Ingraffia. Natural gas is thought to be clean-burning because it produces less carbon dioxide than coal, but methane is released during all phases of production, transportation and burning of natural gas, according to Mr. Ingraffia.

Mr. Ingraffia said “scientists hadn’t been as concerned about the methane component of natural gas,” adding that since natural gas has been increasingly produced domestically, its impact has become more relevant.

When comparing greenhouse gas emissions of shale gas to other forms of fossil fuels, it ranks more than 20 percent higher than coal and diesel fuel, but that footprint shrinks over a 100-year period, and shale gas is comparable to coal, according to the study.

Fugitive emissions also escape from wells after drilling — a typical well has anywhere from 55 to 150 connections to equipment such as heaters, meters, compressors and vapor recovery systems, some of which are specifically designed to vent gas while others simply.

Methane also escapes during processing and transportation, with data available from Texas indicating that average lost gas was 2.3 percent in 2000 and 4.9 percent in 2007, according to the study, which noted this was probably a conservative estimate because the state has resisted legislation capping total losses at 5 percent.

The study, written with Dr. Robert Howarth and Dr. Renee Santoro from Cornell, has received mixed reactions.

“Some scientists said it was a well-intentioned research project. The energy industry said it was hogwash and not worth doing,” Mr. Ingraffia said.

Mr. Ingraffia did caution, however, that that this was only a preliminary study.  “We put it out there and other people will shoot at it. Other scientists will come along and fill up the holes with science,” he said.