BP monitoring storm as spill operations continue

HOUSTON (Reuters) - Choppy seas from a tropical depression near the Bahamas prompted oil-skimming vessels in the Gulf of Mexico to come ashore Thursday, but BP Plc had not evacuated major operations at the site of its massive oil spill.

"No decisions have been made at this stage," spokesman Scott Dean said.

Ships collecting seismic and acoustic data while the leak remains capped during a well pressure test and two rigs that had been drilling a pair of relief wells remain on site, BP said.

The U.S. government's command center confirmed that some skimmers were stopping operations Thursday.

"There has no evacuation of equipment but that could change Some skimmers have been coming in," command center spokeswoman Mary Kahn said.

Transocean Ltd, which operates the relief well rigs, was watching the storm, but no evacuations had begun by midday Thursday.

"Obviously as storm tracks toward the rig, we'd have to take initial actions -- pulling up subsea equipment, securing the location and preparing to move out of the way," Transocean spokesman Guy Cantwell said.

Thursday, the cap on the well was in its seventh day of shutting in all oil flow from the leak.

Wednesday, retired Coast Guard Admiral Thad Allen, the top U.S. official overseeing the spill response, said BP and government scientists were discussing whether to leave the cap sealed or open valves to relieve pressure and let oil gush unchecked if weather forces vessels to move out of the storm's path.

Such an evacuation would include ships operating underwater robots that provide live feeds of the deep-sea well. If they leave, there will be no surveillance for possible problems with pressure at the wellhead for three to four days, he said.

"This is necessarily going to be a judgment call based on the risks associated with the science team," Allen said on Wednesday.

Allen had a briefing scheduled for 2:15 p.m. CDT (3:15 EDT) Thursday. BP had no briefings scheduled as of Thursday morning.

BP and Allen said Tuesday that work had stopped on the first of two relief wells intended to intercept and plug the leak by mid-August to wait out the weather.

BP had placed a "storm packer," or a plug, in the relief well to keep it stabilized until the last set of pipe, or casing, is inserted and cemented in place. Then BP can resume drilling the last 100 feet before boring into the blown-out Macondo well.

Kent Wells, BP's senior vice president of exploration and production, explained Wednesday that the casing must be secured to stabilize the relief well before BP can attempt a "static kill," which would involve pumping heavy drilling mud and cement into the well from the top as the cap keeps the flow shut in.

"We wouldn't want to have that open hole sitting there without the casing" to keep it stabilized, Wells said.

He also said a static kill, if approved, might kill the leak on its own. But the relief well would still be finished to ensure the job's done, Wells said.

Drilling stopped last week on the second relief well, a backup to the first relief well, before the pressure test began.

(Additional reporting by Anna Driver and Bruce Nichols; Editing by Jackie Frank)