New EPA Study Calls Agency’s Own Greenhouse Gas Inventory Into Question

by Ryan Streams, Manager of Regulatory Affairs on June 12, 2017 - 8:33am

EPA’s annual Greenhouse Gas Inventory is an estimate of U.S. emissions from a variety of sources and industrial sectors. Methane emissions from the oil and natural gas industry represent just 3.1% of the total. However, a new EPA study indicates that one of the assumptions EPA uses to arrive at its oil and natural gas estimate may be much too high, calling into question the accuracy of the inventory.

The study involves pneumatic controllers, believed by EPA to be one of the largest sources of methane emissions from well sites. Pneumatic controllers use pressurized gas from the well to move gas and fluids through a network of pipes and valves around the site. In the course of their normal operation, they emit small amounts of methane and other constituents of natural gas.

EPA annually estimates pneumatic controller and other equipment emissions by first estimating the average rate of emissions per piece of equipment and multiplying that by the estimated number installed in the nearly one million active wells across the country. EPA uses a rate of 13.5 standard cubic feet of natural gas per hour (scf/h) for pneumatic controllers, based on a study published in the 1990s and slightly tweaked in 2011.

However, a new EPA study released in April found pneumatic controller emission rates 97% lower than what EPA has been using in the greenhouse gas inventory. The study is the latest in a growing body of scientific evidence that indicates EPA is dramatically overestimating emissions. The new study used several different techniques to measure emissions from a sample of pneumatic controllers in Utah’s Uinta Basin and found an emissions rate of 0.36 scf/h.

In the 2016 Greenhouse Gas Inventory, EPA significantly revised its estimated pneumatic controller count, citing new information indicating there are many more controllers in the field than previously thought. Yet when it was revising equipment counts, it ignored two recent studies showing pneumatic controllers emit far less than EPA estimates. An Oklahoma Independent Petroleum Association (OIPA) study found that intermittent pneumatics typically emit at a rate of 0.4 scf/h. Another by the University of Texas found emissions of 2.2 scf/h. EPA’s new Uinta Basin study is in-line with both these studies. The EPA Uinta Basin study is yet another indication that EPA estimates are inflated.

If real-world emissions are 97% lower than assumed by EPA for one of the most ubiquitous pieces of wellsite equipment, how many others are likewise inflated? What is the effect on the total estimate of industry greenhouse gas emissions? As scientists continue to study pneumatic controllers, pneumatic pumps, tanks, and other equipment, the accuracy of emissions estimates will continue to improve. Rather than ignoring the science, EPA should use these studies and likewise improve the accuracy of the annual inventory.  

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