As the U.S. oil and gas industry emits carbon pollutants like CO2 and methane to the atmosphere, its emissions are tracked closely by federal regulators.
But the federal tracking underestimates emissions of methane, which is the primary component of natural gas, in at least one major natural-gas-producing region in the United States: the Barnett Shale in the Dallas-Forth Worth area of Texas. The results were part of a series of 11 studies funded by the Environmental Defense Fund, an environmental organization, and published yesterday in Environmental Science & Technology.
Emissions from the Barnett Shale were at least 1.5 to 2.7 times higher than reported in U.S. EPA’s greenhouse gas inventory (GHGI) and its greenhouse gas reporting program (GHGRP) for 2013, the study finds.
Almost 40 percent of the emissions were from compressor stations that gather and push natural gas along pipelines. Oil and gas production — as opposed to its distribution, gathering and processing — accounted for 11 percent of the emissions.
Methane has a global warming potential 86 times as potent as CO2 on a 20-year time scale, and the oil and gas industry is the second-largest industrial contributor of the gas. That has made curbing the industry’s emissions a priority for the Obama administration, which is expected to announce draft regulations this summer.
Addressing methane leaks could be challenging when the base-line data contained in federal inventories is faulty.
Small number of sites release the most GHGs
The study, by scientists at the University of Houston, other universities and EDF, finds that Barnett oil and gas sources emitted 46,200 kilograms of methane per hour in 2013. That’s equal to the annual emissions of 243 cars.
The scientists’ production-sector estimates were 31 percent lower than the GHGI and 21 percent lower than the GHGRP.
To arrive at these results, the researchers drove around 152 facilities over 15 days in October 2013. They tested emissions from 125 well pads, 13 compressor stations, two gas processing plants and 12 landfills, which also emit methane in significant amounts.
As in other studies, the scientists found that a handful of sites — so-called super-emitters — were emitting more than their peers (EnergyWire, Sept. 18, 2013).
The scientists estimated that, at any given time in the Barnett Shale, there are 50 well pads, one processing plant and two to three compressor stations that are especially leaky. They constitute just 2 percent of the basin’s sites, but they account for 19 percent of the total oil and gas emissions.
These sites are likely malfunctioning, Robert Talbot, professor of atmospheric chemistry at the University of Houston, said in a statement.
"A lot of them are a broken valve, or someone leaves a hatch open," he said. "It’s human error. And nobody goes back to the site for a month or so."
The study also found that natural gas pipelines that carry the fuel into homes are between 36 and 70 percent less leaky than federal estimates (ClimateWire, April 1).
The American Gas Association, an industry group, pointed out in a statement the reduction was due to its efforts to curb leaks and improve safety.
"A concerted effort by natural gas utilities to upgrade our nation’s pipeline network in order to enhance safety has contributed significantly to a declining trend in emissions from the natural gas distribution system," AGA wrote in a statement.