A plume of methane detected by satellite last month in Canada lined up with the intentional release of the superpotent greenhouse gas from a network of natural gas pipelines. 

SaskEnergy Inc. said its TransGas unit performed relief-valve maintenance at the Rush Lake Compressor station in Saskatchewan on the morning of Sept. 24, releasing natural gas — whose main component is methane — for 10 minutes. A concentration of the gas cloud was observed at 2:15 p.m. local time by a European Space Agency satellite. 

The operator first said it released about 400 gigajoules of gas, but on Wednesday revised that assessment to less than 13 gigajoules, after consulting with onsite teams. Kayrros SAS, a geoanalytics company, estimated an emissions rate of 52 tons an hour based on the satellite data, which is roughly in line with the original figure SaskEnergy provided. 

Kayrros estimated the source of the plume’s location was about 10 kilometers (6.2 miles) from the Rush Lake Compressor station. It was even closer to a TC Energy Corp. pipeline that's part of a vast network that transports natural gas from the Western Canadian Sedimentary Basin to eastern Canada and the U.S.

“We cannot confirm that the image presented was caused by our maintenance work,” SaskEnergy said in an email. “The release was unavoidable for safety reasons. When staff work on equipment it has to be in zero energy safe state, which means any pressurized gas and all electricity needs to be shut down.” 

TC Energy said in a statement that it wouldn't “comment or speculate on third-party information or unvalidated imagery and data.''

Canada is among a group of nations, including the U.S. and the EU, that support a collective goal of cutting methane emissions at least 30 per cent from 2020 levels by the end of the decade, with reductions coming from the fossil fuel industry, agriculture and waste. Still, the Canada Energy Regulator said the companies it oversees don’t have to inform it when they intentionally flare or vent gas. Accidental releases must be disclosed, but the agency said none were reported that coincided with the plume.

Multiple studies have found methane emissions from the oil and gas industry are often higher than what operators and governments report. Releases of the odorless, colorless gas from the U.S. supply chain in 2015 were about 60 per cent higher than the U.S. Environmental Protection Agency inventory estimate, a 2018 study published in Science found.

Halting intentional releases and accidental leaks of methane could do more to slow climate change than almost any other single measure. Methane has more than 80 times the warming impact of carbon dioxide over the short term. The International Energy Agency earlier this month called on fossil fuel operators to do more to curb methane emissions to avoid the worst of global warming.

Many global oil and gas operators have said they are committed to reducing the methane intensity of their operations by cutting back on intentional emissions. The industry is under pressure to respond to increasing investor scrutiny on environmental issues. Still, many operators continue to justify releases as a part of normal operations.

In April, the most severe methane plume ever spotted in Canada based on ESA satellite data analyzed by Kayrros — with an estimated emissions rate of 79 metric tons an hour — coincided with a planned release by TC Energy unit Nova Gas Transmission Ltd. The company at the time declined to provide an estimate for how much methane may have been emitted and said it couldn’t confirm if the satellite observation was related to the event, known within the industry as a blowdown.

A Saskatchewan Ministry of Energy and Resources spokeswoman, Jill Stroeder, said the ministry identified two shut-in wells in the area of the Sept. 24 plume and that a field inspection confirmed they are secure and not the source of any methane release.