For almost 2 days, the US government has withheld final permission for BP to go ahead with crucial but risky pressure testing at the Macondo wellhead. The new sealing cap has the potential to shut off oil flow -- but no one can predict how the well and wellhead will handle the high pressures. The US government has finally given BP the go-ahead, but the going will be very slow.
While conducting the pressure tests, BP will cease containment operations involving the Q4000 and the Helix Producer. It will also halt relief well drilling -- as a further precaution.
The U.S. government has given its approval for BP to temporarily close a sealing cap to shut its blown-out well and determine whether its well casing remains intact, after government officials and scientists reviewed the risk that the operation could result in further, uncontrollable leaks.
Admiral Thad Allen, the administration’s incident commander, said officials exercised “an overabundance of caution” when they delayed BP’s planned shutdown on Tuesday until the company could provide further assurances that it had minimize the risks.
“What we didn’t want to do was compound the problem by making an irreversible mistake,” he said.
Earlier Wednesday, BP vice-president Kent Wells said the company was ready to commence its crucial well-integrity test on Tuesday, but postponed it after a team of company and government scientists wanted further analysis of the risk.
“As much as we want to do things as soon as possible, we also want to make sure they are done correctly,” he said in a morning conference call Wednesday.
The company installed a tight-fitting cap on the blown-out well on Monday and had hoped to begin testing the integrity of the well on Tuesday, a process that could take 48 hours. To do so, it must slowly close valves on the 80-tone cap to stop the geyser of crude for the first time since the well erupted nearly three months ago.
Once the cap is sealed, BP and government scientists will monitor the pressure to ensure well’s cement casing has not been ruptured, which would mean crude is escaping through the space between the casing and the well wall.
If the casing is intact, the company expects to be able to shut in the well until it can complete the drilling of a relief well and plug it permanently sometime in early August. If the casing is ruptured, BP would open the sealing cap and resume funnelling the crude through various collection systems.
Mr. Wells said a team of scientists, working with BP and Obama administration officials, wanted further review of the well integrity test to ensure they properly understood what the pressure readings would imply, and better assess risks that the build of pressure would create additional cracks beneath the surface through which the crude might escape - a risk he described as low.
An unstable area around the wellbore could create bigger problems if the leak continued elsewhere in the well after the cap valves were shut, experts said.
...The cap is just a stopgap measure. To end the leak for good, the well needs to be plugged at the source. BP is drilling two relief wells through the seafloor to reach the broken well, possibly by late July, and jam it permanently with heavy drilling mud and cement. After that, the Gulf Coast faces a long cleanup.
...BP engineers planned to shut off pipes that are already funneling some oil to two ships, to see how the cap handles the pressure of the crude coming up from the ground. Then they planned to close, one by one, three valves that let oil pass through the cap.
Experts said stopping the oil too quickly could blow the cap off or further damage the well.
Scientists will be looking for high pressure readings of 8,000 to 9,000 pounds per square inch. Anything lower than 6,000 might indicate previously unidentified leaks in the well.
“What we can't tell is the current condition of the wellbore below the seafloor,” Mr. Allen said. “That is the purpose of the well integrity test.”
If the cap cannot handle the pressure, or leaks are found, BP will have to reopen the valves and let some of the oil out. In that case, BP is ready to collect the crude by piping it to as many as four vessels on the surface.
In hindsight, it seems obvious that BP should have unbolted the riser and bolted on a new containment cap -- with anti-methane hydrate precautions -- from the earliest days of the leak. But many of these procedures have been developed specifically for this leak, and will serve as a textbook of sorts for future deep sea spills -- which are 100% certain to occur.
Al Fin engineers feel that BP should use the new cap for full containment, together with additional production vessels on the surface. But BP wants to shut the well down as soon as possible, to score a public relations home run and to stop the ruinous daily leakage fines and penalties. Without the total containment effort, an exact measurement of flow rates may not be achieved. It would be a pity to shut the well down at this stage without a definitive flow rate having been obtained -- although recent flow rates may not exactly correspond to earlier flow rates.
It is unfortunate, and frustrating, that the relief well activities have to be temporarily suspended for the pressure tests. Suspension of collection activities on the Q4000 and Helix Producer is understandable, however, for the duration of testing.
If the test results are favourable, BP intends to shut the well down from the top, and then to shut the well from the bottom (bottom kill) using heavy mud, when one of the two relief wells is able to do so. Final killing of the well is predicted to occur in August.
By. Al Fin