Royal Dutch Shell's oil sands upgrading plant near Edmonton, Alberta, caught fire late on Monday and the company said it was taking units off line after crews extinguished the blaze.
Shell and Alberta's energy regulator said the fire ignited after a release of light hydrocarbons and hydrogen sulphide at the 155,000 barrels-a-day Scotford upgrader.
The company said nonessential employees and contractors had been evacuated. No injuries were reported.
The plant turns tar-like crude from Shell's Muskeg River oil sands mine in northeastern Alberta into refinery-ready light oil. It is adjacent to the company's 98,000 bpd Scotford refinery.
The leak occurred on the upgrader's residue hydroconversion unit.
Shell did not say in its statement which processing units at the facility were being shut down, and a spokesman for the Alberta Energy and Utilities Board said he did not know if the plant was fully off line.
The board said it detected no hydrogen sulphide in the air around the plant after the fire. The gas can be deadly in high concentrations.
Shell has a 60 percent interest in the upgrader. Its partners are Chevron and Marathon Oil with 20 percent each.