The conical drilling unit Kulluk in Kiliuda Bay Jan. 8. Photo by Greg Martin for Shell Alaska.

LONDON–Royal Dutch Shell PLC (RDSA, RDSA.LN) Chief Executive Peter Voser said Thursday that both its Alaska drilling rigs need more work before they can be ready for this year’s drilling season.

The Noble Discoverer needs a series of upgrades, while the Kulluk, which recently ran aground, has sustained damage, Mr. Voser said.

“It’s too early to say how this will impact going forward,” he said, referring to the damage of Kulluk on plans to drill this year. The company is also waiting for the conclusion of a number of reviews, both external and internal, into the operating performance in Alaska in the 2012 drilling season before deciding on the next steps, Mr. Voser added.

Write to Selina Williams at Selina.Williams@dowjones.com

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