"Normal repairs and maintenance are routine and ongoing, which we complete on all of our assets," the company said in an emailed statement. "Apart from this routine work, and as previously disclosed, there is a major turnaround planned for Horizon in spring 2013."

Canadian Natural has said it plans an 18-day shutdown at Horizon beginning in May. The work will include a catalyst change, inspections and other maintenance.

(Reporting by Jeffrey Jones; Editing by Gerald E. McCormick)