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A common practice in the oil industry, known as flaring, is believed to reduce methane emissions by burning waste or excess gas from the extraction or processing of oil. But flaring may not be as effective as once thought, according to a new study published in the journal Science.
It is a widely held belief that flaring is 98 percent effective in destroying methane emissions caused by oil and gas exploration. However, according to Eric Kort, an associate professor in the University of Michigan’s Department of Climate and Space and one of the paper’s authors, this assumption has rarely been tested.
Why burn a potentially useful fuel? “You might have a lot of natural gas, mostly methane, that you don’t have anything to do with. They don’t have the capacity to capture it and put it into a pipeline – it’s not economical, the pressure would exceed safety tolerances,” Kort told Ars.
The difference between the assumed efficiency of flaring and the efficiency found in the results by Kort and his colleagues is only a few percentage points. However, the researcher said this seemingly small difference could be a big deal when extrapolated across the fossil fuel industry as a whole. In addition, methane has a more than 80 times greater impact on the planet’s warming than carbon dioxide – at least during the first 20 years it spends in the air.
“By burning [the excess gas] and converting it to CO2 significantly reduces the impact on the climate,” he said.
Take to the skies
Kort noted that oil and natural gas production is often co-located, with oil being the primary reason for co-location. As such, the gas is something of an afterthought. It might be less cost-effective to capture the natural gas and try to sell it, Kort said. “In that case, you’re just going to torch it,” he said, adding that his study doesn’t reflect the natural gas industry, but rather the oil and gas industry. “These wells are mainly for the oil. They only produce the gas together.”
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To study this, Kort and his team studied flaring in three different regions where oil is produced in the US – Eagle Ford, Permian and Bakken Basins. While this may seem limited, these three sites account for more than 80 percent of the country’s total flaring, according to the study. To get a better picture of what’s happening there, the team flew over the three regions in 2020 and 2021.
When considering both inefficient flaring and gas that is not flared, the actual efficiency is about 91 percent, the team found. Inefficient combustion means that flaring does not burn all the methane, which can be for a number of reasons. The pressure in the tube could be wrong, meaning the exit velocity of the gas isn’t quite right, or strong winds could cause the flame to flicker. In either case, the methane ends up in the atmosphere, Kort said.
They used an airplane equipped with equipment to measure carbon dioxide and methane. The team visually spotted flares in the three regions and then flew downwind into the flares’ exhaust plumes. The process then involved pumping air into the instrument from outside the aircraft and using an airborne greenhouse gas analyzer to measure its contents.
The equipment would pick up a large spike in CO2 – which is to be expected considering the flaring aims to produce from the methane. The equipment would also pick up either no methane, some methane, or a lot of methane depending on how effectively the flare destroyed it. In total, the team examined 300 flares in the regions.
To measure when natural gas wasn’t being flared, the team took an infrared camera, pointed it at flare stacks (the tall chimney through which the natural gas flows before burning), and noted when a chimney wasn’t being lit.
Impact could be “quite big”.
While the difference between 98 percent and 91 percent doesn’t seem huge, it can add up, Kort noted. “We… are talking about relatively small percentages, but there are very large amounts of gas [that] burst into flames,” said Kort.
He added that reducing these inefficiencies would result in fewer methane emissions entering the atmosphere and contributing to climate change. This may include ensuring that unlit flares are ignited and ensuring optimal conditions are secured for the flares that are ignited. If these inefficiencies can be addressed and we actually achieve 98 percent combustion, reducing emissions could be equivalent to taking 2.9 million cars off the road every year.
“The impact could be quite large,” Kort said. “This inefficiency has a pretty big impact on the climate.”
Science, 2022. DOI: doi/10.1126/science.abq0385 (About DOIs)