September 16, 2013 | 5
A new study published today in the Proceedings of the National Academy of Sciences finds that methane emissions from shale gas production are substantially lower than previous estimates, adding field data points to a controversial topic.
The study, “Measurements of Methane Emissions at Natural Gas Production Sites in the United States” (PDF), finds that upstream methane emissions from the natural gas industry amount to just 0.42% of gross annual domestic production of associated (oil wells) and non-associated (gas wells) natural gas.
Dr. David T. Allen, chemical engineering professor at Cockrell School of Engineering at The University of Texas at Austin, led the study to quantify methane emission during shale gas production from active production sites. Researchers measured methane emissions during the upstream phase of gas production (exploration and production activities) at 190 onshore natural gas sites with 489 hydraulically fractured wells throughout major shale plays in the United States: Barnett, Eagle Ford, Fayetteville, Haynesville, Denver-Julesberg, and Marcellus.
The measurements indicate that well completion emissions are lower than previously estimated. On a conference call about the study’s results, Dr. Allen said this finding suggests that new “green completion” equipment deployed for well completion is successful at minimizing leaks to the atmosphere. For wells with methane capture or control technology, 99% of emissions were controlled or captured. In 2011, the EPA estimated methane emissions from the US natural gas industry at 81 Mg of methane per well completion, compared with just 1.7 Mg of methane in the Allen study. The EPA relied on engineering assumptions from the 1990s while the Allen study used direct measurements to account for modern operational practices.
However, the results also show emissions from pneumatic controllers and equipment leaks are higher than U.S. Environmental Protection Agency (EPA) national emission projections.
To date, measured data about methane emissions has been limited and drilling and completion processes have evolved in recent years. Recent field estimates by independent scientists including the National Oceanic and Atmospheric Administration (NOAA) have found methane emissions to be 10 to 20 times higher than the UT Austin study. In a 2012 study published in the journal Nature, NOAA scientists found natural gas producers in the Denver-Julesburg Basin in Colorado lost 4% of gas to the atmosphere. This summer, a study published in Geophysical Research Letters found leakage rates between 6-12% for a natural gas field in Utah’s Uintah County.
The amount of lifecycle methane emissions is a key question in the debate about fracking. While natural gas releases fewer greenhouse gases during combustion than coal, the climate benefit is negated if too much natural gas leaks to the atmosphere during extraction and production processes. Natural gas is mostly made up of methane (CH4), which is between 20 to 100 times more potent of a greenhouse gas than CO2 depending on how long it stays in the atmosphere.
Shale gas is extracted by injecting water and other chemicals into shale formations at high pressure to fracture rock and release gas. Much of this water returns to the surface as “flow-back” and is accompanied by undissolved methane, which can escape to the atmosphere. Conventional natural gas wells do not have flow-back. Most studies estimate that an acceptable amount of leakage (or “fugitive losses”) is between 2% and 3% before any climate benefit is negated.
According to the EPA, natural gas systems are the single largest source of anthropogenic methane emissions in the U.S., representing almost 40% of total emissions. Production of natural gas from shale formations currently accounts for 30% of US natural gas production, and is expected to contribute more than 50% by 2040.
The Allen study is already receiving criticism over its results and methodology, arguing that it is not a complete life-cycle emissions study and it ignores conflicting results in the literature.
“Policy-makers and society in general are in great need of robust scientific measurements of methane emissions from modern gas development,” said Physicians Scientists & Engineers for Healthy Energy (PSE) Executive Director Seth B. Shonkoff. “It is disappointing that Allen and colleagues seem to have failed to employ basic scientific rules including transparent criteria for the selection of study sites to measure, sufficient sample sizes, and the attempt to place their results in the context of other scientific studies to date. This study falls short in its attempt to help answer questions about methane emissions from modern gas development beyond the small number of gas industry-selected wells where measures were taken.”
In response to this criticism, Dr. Allen says that the research team picked their own measurement sites and were never refused access to sites.
The study’s release was delayed several times as it underwent several rounds of peer review. A Scientific Advisory Panel, composed of six academic experts in fields relevant to the study, acted as an independent adviser for the study. The study was conducted in conjunction with the Environmental Defense Fund and nine energy companies: Anadarko Petroleum Corporation, BG Group plc, Chevron, Encana Oil & Gas (USA) Inc., Pioneer Natural Resources Company, Shell, Southwestern Energy, Talisman Energy, USA, and XTO Energy (an ExxonMobil subsidiary).
A previous study released by the Energy Institute at UT Austin found no link between fracking and water contamination. That report was surrounded by controversy because of ties between the report’s head author and the oil and gas industry were not disclosed.
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