New Orleans - Energy giant BP extended testing on its Gulf of Mexico oil well to ensure that cracks are not emerging in the seabed after a cap stopped the months-long flow, officials said on Saturday.
The tests, which involve multiple pressure readings on the wellbore that runs to the oil reservoir below the seafloor, have provided "valuable information" and will continue into Sunday, Coast Guard Admiral Thad Allen said.
Once the analysis is complete, BP will open the new cap and resume siphoning off the oil to two production vessels on the sea surface, Allen said.
The tests began Thursday when valves on the cap were sealed, choking off the flow of crude into the Gulf for the first time since the spill began in April.
"Pressure in the capping stack continues to increase very slowly and we want to continue to monitor this progress," Allen said.
"When this test is eventually stopped, we will immediately return to containment, using the new, tighter sealing cap with both the Helix Producer and the Q4000," Allen said in a statement.
"Additional collection capacity of up to 80 000 barrels per day is also being added in the coming days."
BP's return to the containment system was expected to see oil flowing back into the sea once again, at least temporarily, as the pressure in the well is lowered and the new system set up.
Allen added that "progress continues" on the two relief wells, expected to be complete in mid-August, which he recalled are "the ultimate step in stopping the BP oil leak for good."
BP's vice president said earlier Saturday that the cap placed over the gushing wellhead was still holding back spilling crude, but the results of tests on the well's structure require more analysis.
"We're feeling more confident that we have integrity," BP senior vice president Kent Wells told reporters.
"At this point there's not evidence that we don't have integrity."
Wells said indications from the critical tests were that the wellbore was withstanding the pressure created by sealing the leak from above, but the readings were not as clear-cut as engineers would like.
Engineers had hoped to register readings of up to 8 000-9 000 pounds per square inch (psi), a high reading that would mean the well is still intact and there is no seepage.
But the reading Saturday, around 6,745 psi, was inconclusive.
"We could have integrity or we could not have integrity between the 6,000 or 7,500 psi" range, Wells said, though he sounded a note of cautious optimism.
"The fact that the pressure continues to rise is giving us more and more confidence as we are getting through the test," he said.
"The longer the test goes, the more confidence we have in it," he said.
A video feed that has for weeks shown clouds of oil gushing forth at an estimated rate of 35 000-60 000 barrels a day, showed nothing but a white cap and underwater robots Saturday.
The halt, however temporary, of the leak provided a glimmer of hope that the worst oil spill in US history could soon be over, allowing efforts to turn to the grim job of cleaning up hundreds of miles (kilometers) of contaminated shoreline.
Oil has washed up on the coasts of all five Gulf states - Texas, Louisiana, Mississippi, Alabama and Florida - since the spill began April 22, two days after an explosion aboard the BP-leased Deepwater Horizon platform, which killed 11 workers and sank the rig.
The International Energy Agency has calculated there are between 2.3 million and 4.5 million barrels of crude sloshing around in the sea.
A giant skimming vessel, the "A Whale," which officials had hoped would scoop up huge quantities of spilled crude was only able to collect "negligible" amounts during testing and will not be deployed, officials said Friday.
Gulf residents, who are heavily dependent on the fishing and tourism industries have seen their livelihoods ravaged, and the complicated and expensive clean-up process is likely to take years.
BP has so far spent at least $3.5bn dealing with the spill, and compensation claims could eventually cost 10 times that amount, with BP agreeing to set up a $20bn fund to pay damages.
- AFP