* Fires prompt revision to plans for partial start-up
* All units now targeted for August commissioning
* Pelican Lake output seen back to normal in days
CALGARY, Alberta, May 31 (Reuters) - The forest fires that raged across northern Alberta have forced Canadian Natural Resources Ltd (CNQ.TO) to push back the start-up of its Horizon oil sands project by more than a month, the country's largest independent oil producer said on Tuesday.
Canadian Natural said fires and smoke in the region around the facility, which was damaged in an early January explosion, are keeping repair workers from the site, forcing the company to delay and revise its plans for restart.
It now expects to commission all four of the upgrading unit's coker drums at the same time beginning in the first week of August. Ramp-up to the full capacity is expected to start two to three weeks after.
Canadian Natural had previously planned to restart two of the units -- which turn tar-like bitumen from the oil sands into refinery-ready synthetic crude -- at the end of June.
This month, wildfires burned hundreds of square miles of Alberta forests and destroyed about 40 percent of the oil and forestry town of Slave Lake. Fires also forced work-camp evacuations near the oil sands hub of Fort McMurray, including Canadian Natural's.
Workers are expected to be back at the site on June 4.
The company said its expected repair bill for Horizon remains unchanged at C$350 million to C$450 million ($360 million to $465 million), with insurance covering the cost of repairs and business interruption.
Meanwhile, production at its Pelican Lake heavy oil field, which was halted as fires cut power to a regional pipeline, has restarted and is expected to return to the 40,000 barrel a day capacity in the next few days, it said.
The facilities were not damaged.
Another 3,100 barrels of oil and 8 million cubic feet of daily natural gas production near Slave Lake has resumed at about 60 percent flow rates, the company said.
Canadian Natural shares closed up 8 Canadian cents at C$42.17 on the Toronto Stock Exchange. ($1=$0.97 Canadian) (Reporting by Jeffrey Jones; editing by Carol Bishopric)