Thad Allen, head of the US spill response, said monitoring of the well site had not shown any indications of oil leaking from the wellbore and approved continuing the operation.

BP exec Kent Wells said BP continues to work on plans for a “static” top kill and hopes to submit a proposal to the government in the next one to two days.

Wells said there was a “100%” chance BP would undertake the top kill if the government approves the option.

The plan is still in its “infancy,” BP Wells said but scientist will begin outlining how the operation could work.

Under the rough plan, BP would use the existing subsea manifold that is connected to the choke and kill lines of the original Macondo blowout preventer to pump heavy drilling mud down the well.

The mud would push against the flow of oil until it reached the reservoir.

It then might be possible to follow the mud with cement, Wells said.

The first top kill bid was unsuccessful last month when, because of holes in the blowout preventer that allowed mud to escape, BP could not pump enough mud down the bore to overcome the upward pressure of the oil flow.

Static

Wells characterised the second attempt as a “static kill” because the cap provides a closed system that has back pressure to pump against rather than the first “dynamic kill,” attempt, which essentially was pumping contest between the vessels on the surface and the producing reservoir.

It is the first time BP has talked about trying a second kill operation before the relief wells intercept the Macondo bore.

Wells said scientists realised it might be possible when pressure in the capping stack did not build as high as expected.

Because of the low pressure and the closed system, crews would not have to pump at as high rates and pressures as they did during the first attempt, Wells said.

This is important because BP was worried that high pressure could cause some of the components of the well to fail, he explained.

Stable

Even if the top kill is successful, BP will still finish the relief well to ensure that the Macondo bore is shut and stable.

On the first relief well, the drilling team on Transocean semi-submersible rig Development Driller 3 is setting the final casing string, a process that is expected to take another couple days.

The rig is at 17,864 feet and has another 100 feet to drill vertically before it will intercept Macondo, Suttles said.

The relief well about is 4 feet away horisontally from Macondo.

Wells maintained current targets for the operation of intercepting the bore by the end of the month and killing the well by the middle of August.

The Transocean semi-submersible Development Driller 2 has stopped operations and will remain stopped until the first relief well intercepts Macondo, Wells confirmed Monday.

He said that Development Driller 2 was close enough to the Macondo bore that it too would need to begin ranging activities, but having both rigs ranging could lead to incorrect readings.

Testing

Retired Coast Guard Admiral Thad Allen has approved another 24 hours of “testing” beginning Monday, he told reporters at a briefing.

The leak was detected in a flange between the top of the well and the rams that regulate flow up the main bore.

Video footage is showing some hydrate build up on the outside of the stack and scientists believe a small amount of oil and natural gas is leaking out.

Allen said the leak is not expected to hurt performance of the device and is not seen as a threat to its structural integrity.

Video taken by remote operated vehicles have shown some bubbles rising from the top of the 36-inch casing, but Wells attributed it to nitrogen given off by cement used during well construction.

There also have been some bubbles seen coming from the seafloor around the wellhead, Wells said, but initial tests of the bubbles revealed a low methane content, meaning they are likely from natural processes.

Finally, scientists continue to investigate an oil seep found about 3 kilometres from the well head but they do not believe it is related to the pressure testing.

Allen directed BP to carry out investigation into the seep and report findings to the government.

In case the seep does prove to be related, Allen sent BP a letter asking for a written procedure for opening the choke valve as quickly as possible without damaging the well, Allen said in a letter.

Build

Despite early fears about amount of pressure building in the well, all indications are that the wellbore is not damaged, Wells said Monday.

Pressure in the well is currently about 6811 pounds per square inch and building at about 1 psi per hour.

BP continues to shoot seismic surveys of the well site to check for any anomalies that could develop on the sea floor.

In addition, vessels and ROVs are taking acoustic, sonar and temperature readings around the location.

If a blowout were to happen below mudline, BP would open up the valves on the original Macondo blow out preventer, which are attached to the Helix Energy Systems vessels Producer 1 and Q4000, and begin bringing the oil to the surface.

The testing has set back BP plans for a more extensive oil containment and processing system as construction vessels have had to move out of the way during seismic runs.

BP’s latest plan for containment, a system of two vertical risers connecting the choke and kill lines on the original blowout preventer and the new capping stack to four vessels on the surface is about half done.

The first vertical riser is complete and awaiting hook-up, but the second is still being built.

The earliest it could be ready is the end of the month, Suttles said.

Rift

BP and government officials Monday tried to smooth over what appeared to be a rift between the two parties as to how to proceed if the well test ever ends.

Allen had said Saturday the plan was to eventually stop the test and use the capping stack installed over the well to contain the oil and bring it to processing vessels on the surface.

But BP operations boss Doug Suttles said Sunday that BP was taking the test “day by day” and that, assuming there is no evidence of damage in the wellbore, to leave the well shut until a relief well intercepts the bore and pumps it full of cement.

Switching on the containment system would take about three days, Suttles said, during which time BP would have to vent oil into the Gulf of Mexico again.

Suttles was repeatedly asked to clarify the plan during the briefing on Sunday as it seemed an about-face to the statements issued by Allen less than 24 hours before.

During his briefing Monday, Wells made a point of saying how well the two parties were working together and noticeably dodged a question about the potential difference of opinion.

Industry observers say the disconnect may be linked to determining the well's actual flow rate.

Allen said Monday that pressure data from the test would be sufficient to get an accurate flow estimate and the well did not need to be turned on simply to measure the flow.

However, until the well is turned on and all the oil is captured, no one - either within BP or without - will know the true flow rate from the well.

BP could be assessed damages and royalties on every barrel spilled into the Gulf and a measured rate would likely bolster the government’s compensation claims in the future.

The UK supermajor, on the other hand, appears to believe it finally has control of the biggest oil spill in US history and seems reluctant to turn it loose again.

The Macondo oil spill began 20 April with the blowout and explosion of the Transocean semi-submersible rig Deepwater Horizon, which killed 11 people onboard.

Published: 20 July 2010 01:33 GMT  | Last updated: 20 July 2010 21:08 GMT