By Gary Taylor, with Beth Evans and Leslie Moore Mira in New York, Gary Gentile in Washington and Subhan Usmani in Houston

May 6 - BP hopes to begin use of an experimental subsea containment system at its leaking Macondo exploration well in the Gulf of Mexico by May 10, according to BP's chief of operations for America, Doug Suttles.

But he and Coast Guard Rear Admiral Mary Landry emphasized the experimental nature of the containment-dome strategy during the daily press conference May 5 by the Deepwater Horizon disaster task force.

"We are all hoping this will work," said Landry, adding: "This is the first of its kind deployed in 5,000 feet of water. I have to manage your expectations."

Suttles said: "We're doing something unprecedented. There has never been a response of this scale before."

Modified from systems used in shallow water after Hurricane Katrina, this containment system is designed to cover and divert the estimated 5,000 b/d of crude flowing from the Macondo wellhead 4,993 feet below the surface of the Gulf of Mexico about 40 miles from Venice, Louisiana.

Suttles said the containment dome left Port Fourchon, Louisiana, on May 5 en route to the site of the April 20 Deepwater Horizon disaster at the Macondo well (ON 4/22).

By using the container, BP hopes to corral the leaking oil at the wellhead and funnel it up to a waiting vessel at the surface.

Describing the dome as a "large metal building" to cover the wellhead, Suttles said workers and remotely operated vehicles will need two days to place it on the sea floor around the wellhead.

"If all goes as planned, we should start the operation on Monday to stop spilling fluids into the sea," Suttles said.

BP has warned that the containment system likely will contain and divert no more than 85% of the flow from the well even if it works as planned.

After the 100-ton chamber is fitted on the seafloor, it is possible hydrates, or ice plugs, could form, due to the pressure and low temperature, BP officials said during a separate press briefing on the technology employed by the containment system.

The company will run a riser outside the drill pipe to pump warmer surface water down to where the containment chamber is, they said. In addition, methanol will be injected, since it can melt hydrates.

"This has never been done before," said one official during the call. It will "take a few days just to stabilize this system."

After moving to the surface for processing in a drillship, the crude will be sent to BP's Texas City, Texas, refinery and some other Gulf Coast locations for further processing, said the officials. It will be off-spec crude, with extra water in it, they said.

BP officials also said a second containment dome is now being fabricated. But the company would rather not put one over the blowout preventer, where more oil is leaking, since that might hinder their chances to fix the blowout preventer for a better solution, they said.

That containment system is one of several novel strategies being tested by BP in its effort to reduce the flow of oil to a surface spill that is threatening the Gulf Coast from Florida to Louisiana.

BP has also tested the use of special subsea dispersants at the source of the flow, and Suttles said May 5 those tests are now under assessment to determine if it is effective and environmentally safe to continue.

"There was an agreement we would do two test applications, study the impacts and then try to understand it," Suttles said.

He said BP hoped to have a decision on further use of the subsea dispersants by May 6.

The May 5 press conference also featured an appearance by US Interior Secretary Ken Salazar who reaffirmed the Obama administration's determination to make BP fulfill its responsibilities with regard to the incident.

"I have additional questions for BP when I am in Houston in 24 hours," Salazar said.

Reacting to the national impact of the incident, Salazar said: "This spill should call the Clarion question to the entire nation, the question of our energy usage and consumption."

He said it is important for all parties to learn from the Deepwater Horizon disaster "so there is never another incident like it again."

Eleven of 126 workers remain missing and presumed dead in the wake of the Macondo well blowout that also destroyed Transocean's semisubmersible rig Deepwater Horizon as it was closing the well for BP.

BP also conducted its second controlled burn of the spill area May 5 with weather conditions finally allowing a return to that strategy.

In an update on its successful effort to cap one of three leak points in the wellhead, however, BP said in a regulatory filing that success likely will have no impact on the total flow of crude from the well.

"While this is not expected to affect the overall rate of flow from the well, it is expected to reduce the complexity of the situation being dealt with on the seabed," BP said in the filing.

The company also elaborated on its grants to states that might be affected by the Macondo oil spill, noting that it has approved $25 million for each of the four states of Florida, Alabama, Mississippi and Louisiana.

BP said it was able to use remotely operated vehicles to "first cut the end of the pipe to leave a clean end, and the valve, weighing over half-a-ton, was placed on the seabed."

The company confirmed that the valve had securely joined the valve to the broken drill pipe at that location.

BP said ROVs would continue to monitor the well and the remaining flow points for any signs of change.

The company is also said it is hosting town hall meetings in several Gulf Coast communities for volunteers to work on cleaning crews.

Although BP did not provide an update on its primary strategy of drilling a relief well to intercept the flow from the original Macondo well, two US senators told reporters in Washington they understand that well has already reached a depth of 6,000 feet.

The original Macondo well was drilled to a total depth of 18,000 feet.

After a meeting with BP CEO Tony Hayward, senators Mary Landrieu, Democrat-Louisiana, and Bill Nelson, Democrat-Florida, said they had been told that drilling of a relief well was well under way.

In a press release, Landrieu said she was told that a second well is also planned. BP would use the relief wells to intercept the well and inject heavy materials to cut off the flow of oil.

"Work is under way to drill not one, but two interceptor wells," Landrieu said. "The first relief well is currently at approximately 6,000 feet, with approximately 12,000 more feet to go. The drilling of another well is expected to commence soon. This effort is critical to capping the well if the remotely operated vehicles cannot seal the well."

In remarks to reporters after his meeting, Nelson confirmed that estimate.

"They are already down with a relief well 6,000 feet down," Nelson said. "The rest of the going is much harder, much slower, much more rock."

A BP spokesman said the company would not be giving daily updates on the drilling progress, citing the three-month timeframe the company has already given for completion of a first relief well.

As for a second relief well, "we have said we acquired permits to drill up to two relief wells. We will announce that milestone if we need to pursue a second well option," BP spokesman Daren Beaudo said in an e-mail response to questions.

Regarding impact of the spill on downstream operations, a spokeswoman at Chevron's 330,000 b/d refinery in Pascagoula, Mississippi, said it was running normal May 5 while the company monitored the slick.

"Our Pascagoula refinery and other Gulf of Mexico operations are continuing as normal," Chevron spokeswoman Margaret Cooper said.

And a team of analysts at FBR offered their theory on potential causes of the incident, which is expected to undergo an intensive investigation already under way.

"We believe that our analysis shows that a confluence of events outside the control of either Halliburton or Transocean may have contributed to the blowout," said the FBR report, which noted that "we can find no fault so far with anything Halliburton may have done and are thus more confident that the stock should gradually recover as investors gain a similar confidence."

While Transocean operated the rig for BP at the Macondo site, Halliburton performed other oilfield service functions, including cement work on the well.

FBR said that "we do not know for certain whether the operator or Halliburton specified the final choice of cement system, but we believe the decision of which cement system to use ultimately rests with the operator, who is also typically involved in its selection."

The note said that although there is "substantial uncertainty" about the cause of the blowout, "what we do know, however, is that the reservoir was not successfully isolated with cement, that either the casing or the wellhead must have failed, and that the blowout preventer was unable to seal the well."

FBR said that its "current" theory is that "incomplete isolation by the cement allowed a buildup of annular pressure, which contributed to a casing collapse during a negative pressure test, after which the blowout preventer was unable to seal the well due to an obstruction too thick for the blowout preventer to crush/shear, such as a tool joint of drill pipe."