Scientists measure low methane leaks from northeast Marcellus gas fields

 

From a four-engine turboprop plane high above the Marcellus Shale gas fields in Northeast Pennsylvania, scientists measured methane, a potent greenhouse gas.

They found relatively low emissions.

Researchers with the University of Colorado’s Cooperative Institute for Research in Environmental Sciences and the National Oceanic and Atmospheric Administration used their flying chemistry lab to calculate a leakage rate of 0.18 to 0.41 percent of the total gas produced in this region, according to a paper set to publish in Journal of Geophysical Research.

The question of how much methane leaks from shale gas sites is crucial as the U.S. grapples with a transition from coal to natural gas as a fuel for power generation.

Methane is the main component of natural gas. Researchers measured atmospheric methane levels by flying criss-cross patterns over the Marcellus, the Haynesville Shale in Texas and Louisiana and the Fayetteville Shale in Arkansas over one day each in summer 2013. Together, these three basins account for more than half of the country’s annual unconventional gas production, the paper states.

The Marcellus leak rate was the lowest of the three. By analyzing wind patterns and chemical constituents in the air, scientists were able to isolate methane from the shale gas fields below from the influences of agriculture, landfills and urban gas systems.

Weighted for production volume, the authors estimate 1.1 percent of gas produced in the three basins combined is lost to the atmosphere. That’s a lower rate than found in previous studies and near the 1 percent loss rate derived from the U.S. Environmental Agency’s 2012 emissions inventory.

“Some of the early top-down measurements were made in Colorado and Utah, and there the emissions are higher than the EPA emission inventory,” co-author Joost de Gouw, Ph.D., said. “Here in these eastern basins, we have lower leak rates and we’re better in line with the EPA estimates.”

Restrictions coming

As scientists work to understand leak rates, the Obama administration has proposed new regulations that would cut greenhouse gas emissions from the energy sector.

Converting coal-fired power generation to natural gas is one of the four broad suggestions given to states as they try to meet their carbon dioxide reduction goals under the EPA’s Clean Power Plan, proposed last June. This summer, the EPA will announce methane restrictions on the oil and gas industry for the first time.

Though carbon dioxide is the most significant greenhouse gas contributing to global warming, methane has 21 times the global warming potential as carbon dioxide over a 100-year period, according to the EPA.

Natural gas leakage rates must stay below 3.2 percent to provide a climate benefit for power generation compared to coal, according to an influential 2012 study by scientists with Environmental Defense Fund and several universities.

The recent study adds to a growing body of research trying to understand how much methane escapes from gas operations, where and why. Other estimates in various shale gas basins range from around 2 percent to more than 17 percent.

Environmental Defense Fund has taken huge steps to study and address methane leaks, working with academia and the industry to conduct bottom-up studies that measure methane at a specific well site along with top-down studies measuring methane from the air. This month, it published two papers addressing methane leaks from gathering and processing equipment and transmission and storage equipment, associate vice president for climate and energy Mark Brownstein said. The organization did not sponsor this most-recent study.

“No one study is going to give you the perfect answer to the question,” Mr. Brownstein said. “You really have to look at the body of work on this issue.”

Dr. de Gouw said scientists must further study what accounts for the differences in these measurements before they can say for sure whether natural gas has a definite climate benefit relative to coal.

“We need to understand first why there are these differences between different basins,” he said.

The paper puts forth two possible explanations: The abundance of natural gas relative to oil in the three basins and the increasing rate of gas production for each drill rig, as companies learn how to drill high-producing wells more effectively.

In summer 2013, new wells in the Marcellus produced 1.75 times more gas per drilling rig than the new wells in the Haynesville region. This “may partly explain the lower loss rate found in the northeastern Pennsylvania portion of the Marcellus region.”

Solving methane leaks is “not rocket science,” Mr. Brownstein said. He cited an Environmental Defense Fund-commissioned study that estimated gas companies could cut methane emissions 40 percent by projected 2018 levels with simple changes to equipment and practices at a cost of less than 1 cent per thousand cubic feet of gas.

“We know as a practical matter that leaks and equipment malfunction are a large source of methane emissions,” Mr. Brownstein said.

Though Pennsylvania requires leak detection and repair at well sites, the requirement is on an annual inspection basis and should be strengthened, he said.

Combatting leaks

Two gas companies with local operations and a major local pipeline contractor addressed how they combat methane leaks.

Cabot Oil & Gas Corp., the northeast Marcellus’s top producer, reduces methane leaks through special equipment, engineering designs and monitoring, spokesman George Stark said.

Cabot installs no-bleed gas processing units — those metal boxes with vertical stacks seen on producing well sites — and brine tanks, he said. The company will often retrofit its older sites with more modern equipment when possible, he said.

It’s also transitioned to welding the seams between pipes instead of threading them, reducing the potential for small leaks, he said. They also design well sites to use the least amount of pipe possible and bury the pipe they use.

Cabot can now use local gathering lines to capture gas during the well completion process and send it through pipelines instead of burning it off in a flare, he said, though it still uses flares occasionally. The process is known as “turning in line.”

Southwestern Energy Corp. uses turned-in-line completions, closed loop systems that recover gas during engine blowdowns and vapor recovery systems on glycol reboilers and storage tanks, spokesman Mike Narcavage said. The company also participated in an Environmental Defense Fund-sponsored study of well site methane emissions.

Specifically in Pennsylvania, the company’s pipeline subsidiary is in the process of converting to air-bleed systems its pneumatic valves that regularly emit puffs of gas, he said.

Linde Corp., a Pittston Twp.-based contractor with extensive involvement in pipeline work across the northeastern Marcellus, has used leak-preventing welding and testing techniques for years, spokesman Kevin Lynn said.

All pipelines segments are joined by welds, he said. When complete, each weld is marked with GPS coordinates and checked with an X-ray device. The entire line is also pumped with water at 2,250 pounds per square inch for eight hours to test its integrity, he said.

Most pipeline companies Linde Corp. works with have a one-strike rule for their contractors, he said.

“If you have a weld that fails the X-ray, you’re pretty much thrown off the job,” he said.

Cabot and Southwestern participate in the EPA’s voluntary Natural Gas STAR Program, which encourages members to attain more ambitious methane emission goals than regulations require. Chesapeake Energy,, Kinder Morgan, Williams and several UGI companies also participate.

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bgibbons@timesshamrock.com, @bgibbonsTT on Twitter