One of the cokers at Syncrude has been shutdown for unexpected repairs. (Jeff McIntosh/The Canadian Press)

Canadian Oil Sands Ltd. is lowering the amount it expects to produce at its massive Syncrude facility north of Fort McMurray this year because of an unexpected breakdown at one of the facility's cokers.

The "unplanned maintenance," as Syncrude calls it, at coker 8-1 will knock the unit offline for a while. The company isn't saying how long, beyond that it expects the work to overlap with a planned shutdown of another coker, 8-2, which is scheduled for the second quarter of this year.

Having both cokers offline at the same time will slow production significantly.

The cokers are integral to the process of converting thick oilsands bitumen into a lighter, more liquid product that can be piped or shipped to refineries for processing.

As a result, the company "has revised its estimate for the annual Syncrude production range to 95 to 105 million barrels," of synthetic crude this year, the company said in a release.

In December, the facility was forecast to produce as much as 110 million barrels this year.

A boiler related to the coker in question also broke down last year, which caused the coker to be shut down ahead of schedule and lasted for almost two months. 

Canadian Oil Sands is the largest shareholder in the massive Syncrude project, but Imperial Oil, Sinopec, CNOOC and Suncor are also minority partners.