BP hopes oil well cap has stopped leak as it gets ready for 'kill'

• Even after the well is finally sealed the clean up will go on (photo: Getty Images)

Doug Suttles, BP's chief operating officer, said that a new cap fitted on the well's broken riser pipe last week will be kept closed indefinitely, blocking further oil from leaking into the water, while scientists continue a "well integrity test" to check for leaks below the sea bed.

Unless data readings taken inside the well indicate trouble, he said, BP hoped to keep the cap shut "all the way along to the point where we can get the well killed" - a procedure that is due to begin in the final days of July and should be complete by 13 August.

The kill process is the only method that can end the crisis, sealing the well permanently with mud and cement, though keeping the cap closed should ensure that no further oil is spilled in the meantime.

"Nobody associated with this activity, whether it's BP or government groups or the people who live along the Gulf coast wants to see oil again," he said.

But he added that the situation would remain under constant review.

"Clearly we have to make sure that we don't make the situation worse and that's the reason we are taking this integrity test so cautiously.

"We will just take this day by day. We don't want to have to reinstate oil into the Gulf if we don't have to, but if we do have to we will," he said.

The decision on whether the well has to be reopened at any point rests with the national incident commander, Admiral Thad Allen, who appeared more cautious yesterday.

While Mr Suttles described the pressure readings inside the well as "encouraging", Adm Allen stressed that they were "lower than expected," not fully understood, and did not rule out that the well may be unstable. He was due to decide last night whether to extend the shut-in.

"Work must continue to better understand the lower-than- expected pressure readings. This work centres on two plausible scenarios, depletion of oil from the reservoir and potential leakage caused by damage to the well bore or casing," he stated.

"While we are pleased that no oil is currently being released into the Gulf of Mexico and want to take all appropriate action to keep it that way, it is important that all decisions are driven by the science. Ultimately, we must insure no irreversible damage is done which could cause uncontrolled leakage from numerous points on the sea floor."

The best-case scenario after BP closed the containment cap on Thursday, halting the oil flow for the first time in nearly three months, was that pressure inside the well would build to more than 8,000 pounds per square inch, a sure sign that the well bore was not damaged in the 20 April explosion.

If it dropped below 6,000psi, it would indicate a break below the seabed. But the pressure stood at 6,778psi yesterday and was increasing at a rate of one to two psi per hour, leaving the test still in a grey area.

Extra measures have been put in place including seismic surveys of the sea bed and acoustic and visual monitoring, to check that in continuing to hold the well closed, oil is not being squeezed out through a hidden break under the seabed.

Meanwhile, the main relief well has now reached a depth of 17,864ft below the sea's surface. Technicians will spend the next week laying the final stretch of steel casing inside it, then continue drilling until the two wells intersect, allowing them to pump in mud and cement to kill the Macondo.

The kill operation is due to begin during the last few days of this month, and could take up to two weeks.

Mr Suttles said: "The last two and a half days have shown encouraging results but these are just early steps and it's critical that we recognise we'll be here for the long term. Even after we get this well killed off so it can never flow again, we still have to clean up."