Vessels work the late shift above BP's Macondo wellhead, source of the Gulf of Mexico oil spill, on Tuesday, one day after a new oil-containment cap had been fitted to the gushing pipe a mile (1.6 kilometers) below. (See Gulf of Mexico map.)
Thursday afternoon BP announced the new cap had been fully sealed during a crucial "integrity test" and that oil had completely stopped leaking from the site for the first time since the Deepwater Horizon oil rig exploded and sank on April 20.
The welcome development comes after a roughly 24-hour delay, during which experts scrambled to allay U.S. government scientists' fears that the test could further damage the well.
"This last minute evaluation was due to an overabundance of caution," said Coast Guard admiral and response-team leader Thad Allen in a press briefing Wednesday evening. "We sat long and hard about delaying this test. This was not easy."
Thursday morning BP delayed the test one last time after workers had discovered a leak in the so-called choke line, which allows oil from the cap to be siphoned to the surface.
But, BP Senior Vice President Kent Wells told reporters early Thursday, "fortunately we had a second choke on surface ... and we're once again going through the process of positioning ourselves to do the well integrity test."
BP's integrity test should determine whether the new oil cap can remain sealed without causing a dangerous buildup of pressure in the well.
Gas and oil leaks from the previous containment cap at the Gulf of Mexico spill site in a picture from a live BP video feed on Saturday.
Installed June 4, the old cap, nicknamed "Top Hat," was removed on Saturday to make room for a bigger, tighter fitting cap. The new cap, as of Thursday afternoon, has completely stopped the Gulf oil leak, according to BP.
The containment caps are designed mainly to help pipe the primary flow of oil from the broken BP wellhead to collector ships on the surface of the Gulf of Mexico.
The old cap was replaced Monday by a bigger, snugger cap called "Top Hat Number 10." If the new cap works as intended, it will allow the capture of between 2.5 to 3.4 million gallons of oil a day—or about double the amount of oil collected with the old containment cap.
But some experts worry the new cap could work too well.
U.S. Energy Secretary Stephen Chu, among others, expressed concerns that a tighter-fitting cap will allow too much pressure to build up inside the well, potentially rupturing it and causing oil and gas to leak into—and up out of—the surrounding seafloor. In place of one oil leak, there could be several.
Oil gushes from the uncapped BP wellhead on Saturday after the old "Top Hat" oil-containment cap was removed to make room for the tighter-fitting cap.
With no cap in place, more than 5 million gallons (19 million liters) of oil are estimated to have gushed out into the Gulf of Mexico during the two days before the new cap was installed.
BP and Coast Guard officials stress that the caps are just a temporary fix until the drilling of permanent relief wells is finished in mid-August. (Read more about the Gulf of Mexico relief wells in "Gulf Oil Leaks Could Gush for Years.")
Once the relief wells reach the broken well, they will be stuffed with heavy drilling mud and cement and should stop the flow of oil completely, according to BP.
Image courtesy BP via Reuters
New BP Cap Lowered Into Gulf
A portion of BP's new containment cap is lowered into Gulf waters at the Deepwater Horizon wellhead site on Sunday.
The new cap was installed by Tuesday, but due to concerns from U.S.-government scientists, BP delayed a critical test of the containment cap's integrity.
"As much as we want to do things as soon as possible, we also want to make sure they are done correctly," BP Senior Vice President Kent Wells said in a morning conference call Wednesday.
A major concern is that the new cap will allow too much pressure to build up in the oil well. If, during the integrity test, pressure in the well hovers around 9,000 pounds per square inch (psi), then it will indicate that the well's structure is sound and the cap can be kept closed.
If the pressure drops to around 6,000 psi, however, it would mean that too much pressure has built up inside the well and that gas and oil is leaking into the surrounding sea floor through a new crack.
BP's new containment cap—pictured Monday during installation—could prove handy during a hurricane.
Normally the cap would feed valuable oil to pipes connected to collector ships. But it could potentially be sealed completely during strong storms, which may force ships to leave the oil-spill site, Coast Guard Adm. Thad Allen told reporters Wednesday.
"We have good weather right now, and we'll try to take advantage of that, as you know," he said. "But if we have to leave the site ... we need to know whether or not we can just cap the well and leave."