BP Exploration (Alaska) Inc. is halting production from about 150 North Slope oil wells “as a precautionary measure” while the company “confirms the integrity of subsurface well casings in wells with high outer annulus pressures,” BP said in a statement at 7:30 p.m. on Aug. 24.
An annulus is the space between the steel pipes, or casings, used to construct an oil well, BP said.
The shut down is expected to reduce North Slope production by about 60,000 barrels of oil per day, representing about 6 percent of total ANS production, the company said.
A BP employee was seriously injured Aug. 16 when a casing burst on a Prudhoe Bay well A-22, resulting in an explosion and fire. Prior to the incident, pressures in excess of 2,000 pounds per square inch were recorded in the outer annulus of the well, BP said.
A team of BP operators and technical experts investigating the accident recommended the company “halt production from about 150 wells with outer annulus pressures greater than 1,000 pounds per square inch until casing integrity can be confirmed, the cause of the A-22 casing failure is determined and procedures for the operation of these wells are reviewed and revised,” BP said.
“Casing used in the construction of the well had an original pressure rating in excess of 5,000 pounds per square inch. The investigation team so far has been unable to determine why the outer annulus casing failed at a pressure significantly lower than its original pressure rating,” BP said.