Devon Energy Corp. has shut down seven wells at its Jackfish oil sands site after a failure at one of the wellheads sent a plume of bitumen-laced, high-temperature steam into the air for nearly 36 hours last weekend.
The leak began Saturday afternoon and was stopped Sunday at midnight.
"It's what we would call a steam release leak and it did have bitumen in it," spokeswoman Nadine Barber said. "That bitumen took the form of a mist or a spray."
The company said it did not know the cause of the leak, nor how much petroleum was spilled, although it said bitumen coating the ground near the leak has made it difficult to work in the area.
Jackfish produces 35,000 barrels per day. Devon said several thousand barrels a day of production have been halted, and it's unclear when that will resume. It could take two to three weeks to clean up the spill, Ms. Barber said.
"No employees, no contractors, no community members were injured as a result," Ms. Barber said. "There is no immediate threat to anyone in the area, including the community, and no evacuation required."
Still, environmental groups say the oil could have made its way into Sunday Creek, which flows into a network of major rivers in north-eastern Alberta.
Jackfish is located roughly 170 kilometres south of Fort McMurray, and 15 kilometres from the town of Conklin.
Devon employs what's known as steam-assisted gravity drainage, or SAGD, at its Jackfish site. Using that process, high-pressure steam is injected into the ground using a horizontal well; that steam then heats the bitumen, melting it out of the sand and causing it to flow into a second horizontal well that brings it to surface.
The leak happened in what industry calls the "producer well," which extracts the bitumen.
The company uses what it calls a "pad" to drill multiple wells. The leaking well was on a pad with seven wells in total; all have been shut down for now.
Both Alberta Environment and Alberta's Energy Resources Conservation Board are investigating the leak.
SAGD projects use intense pressure and temperature, and this is not the first SAGD accident in the oil sands. In 2006, a well at Total E&P Canada Ltd.'s Joslyn site blew through the earth above it, sending rock flying hundreds of metres into the air. A regulatory report found that the company used greater pressure at the site than it was allowed to.
The industry has held up SAGD -- and other methods that don't involve mining -- as the future of the oil sands, 80 per cent of which will be extracted without mines. SAGD is also often seen as a more environmentally palatable approach, since it doesn't scar the landscape the way open-pit mines do.
However, accidents at SAGD sites have caused some to question how much better that technology is.
"This blowout, along with Total's fiasco, suggests major risks with in-situ development," said Andrew Nikiforuk, an author who wrote "Tar Sands: Dirty Oil and the Future of a Continent."
Mike Hudema, a Greenpeace campaigner in Alberta, said the spill should be seen as a warning sign.
"Accidents like this are bound to happen which further contaminate our landscapes, further poison the environment and also potentially affect surrounding communities as well."