Rates at Buzzard will be limited to the equivalent of about 80,000 barrels of oil daily until the work is completed, Calgary-based Nexen said in a statement. Production will be ramped up to full capacity of 200,000 barrels a day by the end of July. A two-week turnaround at Buzzard scheduled for September has been realigned because of the cooling work.

The company said its 2011 output would be at the low end of the guidance issued in November. The company had forecast output would average 230,000 to 270,000 barrels a day before royalties.

Nexen’s fields in Yemen were returned to full production May 11 after being shut for two days because of a labor dispute, according to the statement. The company also said it plans to drill two exploration wells in the U.S. Gulf of Mexico this year and expects output to start from a field off West Africa next year.

The company’s Long Lake oil-sands project is producing 28,300 barrels a day, Nexen said. The company performed maintenance on parts of the project in April and will do further work in August.

Nexen slipped 15 cents to C$22.09 on the Toronto Stock Exchange. The shares have dropped 3.1 percent so far this year.