Three Environmental Defense Fund-affiliated studies this month make some pretty alarming claims about oil and natural gas methane emissions in the Permian Basin and Gulf of Mexico. But a closer inspection of the methodology behind these much higher than previously reported leakage rates shows that EDF is using calculations outside of the norm – some at odds with what the group has recommended previously – and they’ve been doing it for awhile.
Do As I Say, Not As I Do
Calculating methane emissions is a complicated task, and results can vary depending on how measurements are sampled, how often a site is evaluated, how large of an area is being sampled – they can even be influenced by time of day and weather. When researchers give a rate of methane emissions (intensity), what they are usually doing is calculating the total oil and natural gas methane emissions that they measured (or estimated for a region based on a smaller sampling) and dividing that by production.
There’s some debate on the amount of production to include in intensity calculations: Does it make more sense in an oil play to calculate intensity by total oil and natural gas production (barrel of oil equivalent) or only by total natural gas production? While there’s merit to both of these arguments, for the sake of consistency, EDF made its position clear on this in April 2018:
“Though there are different ways to calculate an upstream oil and gas intensity target, generally we recommend: Total methane emissions from oil and gas production / Total natural gas production.”
Or so it seemed.
Just a couple of months later, a study authored by EDF researcher Ramon Alvarez and his colleagues used methane produced rather than total natural gas produced to compare the amount of methane emitted, further inflating their percentage. This 2018 study was the beginning of a series of nearly identical EDF-affiliated studies, all of which follow the same methodology that lowers the denominator in calculating intensity, thereby raising the rate. Why is EDF advising others to use total natural gas production, while not doing so itself?
Top Down, Not All Around
These studies dismiss holistic data collection methods, ultimately failing to collaborate with industry to adequately respond to these leaks. Top-down studies like these give way for a potential overestimation of emissions from other sources. In fact, a National Oceanic and Atmospheric Administration study found that top-down studies likely overestimated emissions by mischaracterizing episodic emissions as normal emissions.
“Emissions from production facilities are not constant and include non-trivial temporal complexities”
While EDF tried to discredit NOAA’s study in in Alvarez et al., the group’s new studies show the potential downsides to using only these methods.
This month, the Journal of Environmental Science and Technology published a study by Negron et al. which claimed methane emissions from offshore platforms in the Gulf of Mexico are higher than those reported by the U.S. Environmental Protection Agency Greenhouse Gas Inventory (GHGI). The researchers found deepwater platform estimates were consistent with the reported amounts, but shallow water rigs – with an estimated 2.9 percent leakage rate – had higher loss rates than reported. Negron et al. acknowledge the potential episodic nature of their data:
“High emissions may be released from nonroutine venting during a blowdown for equipment depressurization in maintenance operations associated with turnarounds or shut-downs.”
In that same vein, a study by Zhang et al. released last week in Science Advances used satellite data to claim that Permian Basin methane emissions are much higher than those reported in the GHGI. In this study, the researchers found a leakage rate of 3.7 percent, nearly 60 percent higher than the national rate.
The exclusive use of top-down data collection methods demonstrates the lack of collaboration with industry with these studies, which may have resulted in higher emissions estimates than what’s actually occurring.
No Action, No Results
Responsible operators across the country are actively working to lower their methane emissions, and as EID has previously explained, EDF claims to be a part of working toward solutions to do so. Nonetheless, instead of notifying operators that a potential issue exists so that it could be evaluated and fixed, EDF sat on this data for months. Oil and natural gas operators had the ability to adequately respond to these reported leaks, instead these researchers followed EDF’s approach, and simply garnered headlines, not results.
As Zang et al. identified, there was no indication of increased methane emissions in the Permian over the study period, despite significant increases in natural gas production – a testament to the efforts being made by industry to reduce these emissions. With improved technology, and as more pipeline takeaway capacity comes online, Permian emissions will continue to fall. As the ONE Future Coalition – a group of natural gas companies that have the central goal to reduce methane emissions intensity to one percent in the next five years – explained in its 2019 progress report:
“Overall methane intensity decreased by 41%, demonstrating that the natural gas industry can minimize methane emissions and increase production and throughput while supplying much needed energy to the U.S. and around the globe for years to come.” (emphasis added)
