Nearly a month after Royal Dutch Shell PLC abandoned plans to drill into the oil reservoirs on its offshore Arctic leases, the Coast Guard on Thursday certified the company's main oil containment barge, the Arctic Challenger, for future operations.

However, Shell is still repairing its oil spill containment dome, which was damaged during the company's final round of inspections in mid-September. Shell expects to complete work on that piece of equipment by the end of the year, according to company spokesman Curtis Smith.

The containment dome accident ended the Dutch company's hopes of measuring the volume and pressure of the oil on its Beaufort and Chukchi seas leases during this year's open water season (EnergyWire, Sept. 17).

Instead Shell is drilling preliminary "top wells" to prepare for next year's drilling season. Those operations must stop short of the leases' oil-laden rock.

Coast Guard officials said the Arctic Challenger certification was based on more than 600 inspections and reviews relating to its design, construction, safety systems, structural mooring and electrical equipment. The authorization is good for five years, although the vessel must be rechecked each year.

The Challenger was also given the green light by the American Bureau of Shipping, which sets design and construction standards for marine vessels and offshore structures.

Coast Guard officials said the Challenger's review was concentrated into a six-month period in an effort to accommodate Shell's Arctic drilling program. Usually, reviews can take up to 18 months.

Shell's Smith described the vessel's Coast Guard certification as "welcome news [which] means Shell will have the necessary assets in place to drill and evaluate hydrocarbon zones in 2013."

Shell is also disclosing some of the details of the spill control equipment accident that ended this year's hope of drilling for oil.

Smith said in an email that the Arctic Challenger's dome "was damaged when it descended too quickly due to a faulty electrical connection that improperly opened a valve. While safety systems ensured it did not hit the bottom, buoyancy chambers were damaged from the sudden pressure change."

He added that the company is modifying the dome to prepare for next year's operations. Final approval of the spill response equipment rests with the Interior Department's Bureau of Safety and Environmental Enforcement.

The Arctic Challenger, built in 1976, was extensively overhauled to serve as Shell's primary spill response vessel in the Arctic. The company voluntarily included the containment dome in the aftermath of the 2010 Deepwater Horizon oil rig disaster.