An extensive airborne survey of a previously identified methane hot spot in the US Four Corners area found that just 10% of the individual observed sources contributed half of the emissions, the National Aeronautics & Space Administration reported.
Five trade associations representing the upstream oil and gas industry responded that the study was a good first step, but is narrow in scope compared with others now under way and expected to be more comprehensive.
Scientists from NASA’s Jet Propulsion Laboratory and the California Institute of Technology, both in Pasadena, Calif.; the National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colo.; and the University of Michigan at Ann Arbor used two JPL airborne spectrometers to identify and measure more than 250 individual methane sources, JPL said.
Methane emissions in the area where Arizona, Colorado, New Mexico, and Utah meet are associated primarily with coalbed methane (CBM) production and transportation, NASA said. The sources emitted the gas at rates from a few to 11,000 lb/hr, JPL added. Results were published in a paper, “Airborne methane remote measurements reveal heavy-tail flux distribution in Four Corners region,” in the Proceedings of the National Academy of Sciences.
The experiment proved that an airborne methane detection concept works, according to lead author Christian Frankenberg of JPL and Cal Tech. “That we could observe this distribution in a widespread geographical area and collect enough plumes to perform a statistical analysis was a pleasant surprise,” he said.
A 2015 investigation
Frankenburg and other researchers originally detected the Four Corners methane hot spot using past observations from a European satellite, JPL said. Last year, he and JPL colleagues joined a campaign, led and funded by NOAA, to investigate the hot spot, called Twin Otter Projects Defining Oil/Gas Well Emissions (Topdown). The campaign also included researchers from the University of Michigan. Each participating institution deployed its own suite of instruments.
The study’s observed emissions sources included gas processing facilities, storage tanks, pipeline leaks, and well pads, as well as a coal mine venting shaft. “With the observed confirmation of a lognormal emission distribution, this airborne observing strategy and its ability to locate previously unknown point sources in real time provide an efficient and effective method to identify and mitigate major emissions contributors over a wide geographic area,” it said.
It said that the US Environmental Protection Agency uses a process-based approach that assumes a normal distribution of emissions for each process used in extraction, processing, and distribution. In reality, the flux distribution can be heavily skewed, resulting in a heavy-tailed distribution.
This suggests that a relatively small percent of the sources in a given field may dominate the overall total, the study said. “Although the heavy-tailed distribution makes it more difficult to estimate emissions using a process-based (or bottom up) approach, it suggests that mitigation of field-wide emissions such as those estimated for [the Four Corners area] will be less costly because it only requires identifying and fixing a few emitters,” it said.
“However, evaluating the distribution and role of point sources in large geographical areas with limited road access is too time-consuming without prior knowledge of suspected locations,” the study continued. Researchers conducted an intensive airborne campaign in April 2015 to overcome this shortcoming and directly measure the source distribution, identify strong emitters, and provide real-time feedback to ground teams.
Strong emitters dominant
“Our analysis shows that strong emitters dominate the regional budget, with presumably lower marginal cost for emissions reductions. We have also demonstrated the ability to quantify and identify both small and large point source emissions widely spread over inaccessible geographic areas,” the study concluded. “Airborne remote measurements, combined with in-situ sensing, could thus provide a path forward toward effective methane emission (monitoring) mitigation strategies.”
But the oil and gas trade associations in Colorado and New Mexico said that several other studies under way by NOAA, the University of Colorado, and the University of Michigan in conjunction with NASA will include on-the-ground measurements of all Four Corners area methane sources of methane, including coal mines, landfills and natural seeps.
“The study represents a snapshot in time that can provide valuable information, but is not suitable for extrapolation to monthly, annual or other longer-term emissions estimates,” said Christi Zeller, executive director of the La Plata County Energy Council.
“Certain operational events, such as scheduled maintenance downtime, are temporary and can skew results,” she said. “For example, one gas plant was measured five times, with one outlier measurement that occurred during a scheduled maintenance event. We look forward to the results from NOAA and the universities to provide a more complete picture of methane in the area.”
New Mexico Oil & Gas Association Pres. Steve Henke said, “The first of several studies, NASA’s assessment begins the process of better understanding methane levels in the region, but it addressed a limited set of methane sources. It has been known by the states and tribes in the Four Corners that natural methane seeps occur throughout the area from the Fruitland Formation outcrop. Also, the topography of the area traps air and causes methane to build up over time, whether from human or natural sources.”
Small methane amounts offset
Kathleen Sgamma, vice-president of government and public affairs at the Western Energy Alliance in Denver, noted, “There is a built-in economic incentive for producers to minimize emissions and capture as much methane as possible, since it’s the very product they sell.” Small amounts of methane emitted at the well site are offset many times over by the huge greenhouse gas reductions natural gas delivers when used to generate electricity, she said.
Colorado Oil & Gas Association Pres. Dan Haley said, “Oil and gas operators in Colorado strive to protect the health and safety of our communities and environment every day; after all, these are the communities where we are raising our families. Colorado and the nation have seen a significant decrease in greenhouse gas emissions due to an increase in the electricity powered by gas.”
The US Energy Information Administration projects that carbon emissions will be lower in 2040, largely because of gas-fired power generation, according to Colorado Petroleum Council Executive Director Tracee Bentley. “Put simply, increased use of gas has been at the heart of America’s climate progress and will continue to play a major role in emissions reductions well into the future,” she said.
Oil and gas production has taken place in the Four Corners area’s San Juan basin since the 1940s, the five associations jointly said. In its northwest New Mexico portion, where there are nearly are nearly 20,000 active gas wells and just under 2,000 oil wells, about 140 operators produced 646 bcf of gas in 2015.
In the San Juan basin’s southwestern Colorado portion, where about 34 operators produced 337 bcf of gas the same year, there are about 3,400 active wells, about two thirds of which are CBM and one-third conventional gas, the groups said.
Contact Nick Snow at firstname.lastname@example.org.