(Adds details about refineries, updates headline)

By Ayesha Rascoe

WASHINGTON, Sept 15 (Reuters) - Hurricane Ike caused minimal damage to oil refineries in the Gulf of Mexico, the U.S. Energy Department said on Monday.

Companies were preparing to restart operations at the 14 oil refineries in Texas and Louisiana that remained shut due to Ike. The closed refineries have a total capacity of 3.573 million barrels per day, the department said.

Valero Energy Corp <VLO.N> reported no major structural damage, although the company's Texas City and Port Arthur refineries are still without power. Shell Oil's <RDSa.L> Deer Park, Texas refinery suffered some damage and still had no electricity Sunday. The Energy Department reported Exxon Mobil Corp's <XOM.N> Beaumont, Texas refinery is also without power.

In addition, 27 major natural gas processing plants with a total capacity of 13.85 billion cubic feet per day were closed in the Gulf of Mexico, including plants still affected by Hurricane Gustav.

Eight major natural gas plants with a total capacity of 2.9 billion cubic feet per day were operating at reduced or normal levels.

Strategic Petroleum Reserve sites in Bryan Mound and Big Hill, Texas, and West Hackberry, Louisiana remained shut down as of Sunday. The Bayou Choctaw, Louisiana reserve site was operational.

The Energy Department has granted several requests for emergency oil in recent weeks. Citgo Petroleum said Sunday it asked the department for 1 million barrels of oil from the Strategic Petroleum Reserve due to supply disruptions from hurricanes Ike and Gustav. The Energy Department was reviewing Citgo's request, a DOE spokeswoman said on Monday.

Nearly 3.9 million customers were without power in the aftermath of Ike. In Texas, which was hardest hit by the storm, about 2.4 million customers remained without power. (Reporting by Ayesha Rascoe; Editing by Marguerita Choy)

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