Planes and helicopters grounded by the storm are just now being cleared for takeoff, and it's likely to take several hours to reach and survey the structures farthest out in Gulf waters.
On the New York Mercantile Exchange, crude for October delivery fell 48 cents to $43.10 a barrel and the October natural gas contract sank 13.9 cents to $4.685 per million British thermal units, indicating traders' concerns about structural damage are easing.
See Futures Movers.
About 25 percent of U.S. oil and gas output comes from the Gulf.
On Thursday afternoon, Diamond Offshore (
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Aircraft surveillance of the rig, operating in deep water, showed no apparent damage and efforts were underway to re-board it, Diamond Offshore said in a statement. Four other Diamond Offshore rigs in the storm's path were still on location and appeared to have weathered the storm, the company added.
ExxonMobil (
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"Production remains shut in for all of our offshore central and eastern Gulf of Mexico platforms and our onshore and offshore Mobile Bay facilities," said Susan Reeves, spokesperson for the Dallas-based energy giant.
"As soon as power is restored to the facilities and people are allowed back to the affected areas, then we'll begin our assessment process to determine the integrity of our equipment," she said.
BP (
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"Before we put people back onto facilities, we need to make sure it's safe," said BP spokesman Hugh Depland, adding flights should take place Thursday. "At that point, we'll be able to judge when we'll be able to put people back onto facilities."
According to a statement on Shell's U.S. Web site, the company has scheduled some personnel to return to work Thursday and the rest on Friday.
Shell Exploration & Production Co. "will now focus on damage assessment, recovery, and returning personnel to work," the parent company (
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Ivan had halted production of 444,800 barrels of oil a day and 1.44 billion cubic feet of gas daily.
Also, Shell's Louisiana refineries, Norco and Convent, were undamaged by Ivan. There were no injuries at the facilities, and the refineries will begin restart procedures Thursday, the company said. Each refinery has a processing capacity of 225,000 barrels per day.
At ChevronTexaco (
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As for its Pascagoula, Miss.-refinery, Chevron expects to complete aerial reconnaissance of the site by Thursday afternoon. The refinery processes 325,000 barrels of crude oil daily.
"We won't be able to fully evaluate until conditions in the area are safe enough for people to return," Carmichael said.
Jeff Callender, a spokesman for ConocoPhillips (
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The refinery has a processing capacity of 250,000 barrels of crude a day, and the restart process can take as much as seven days, he said. There were no initial reports of damage.
On Wednesday, the Minerals Management Service reported that workers on 575 platforms and 69 rigs had been evacuated from the Gulf of Mexico, representing 75.3 percent of 764 manned platforms and 59 percent of currently operating rigs.
The reduction amounted to 77.6 percent of the 1.7 million barrels per day of oil produced out of the Gulf. Similarly for natural gas, about 49 percent of the 12.3 billion cubic feet of output is affected.
Lisa Sanders is a Dallas-based reporter for CBS.MarketWatch.com.