This third containment effort, which includes a free-standing riser pipe that can be quickly detached in the event of a hurricane, had been delayed by rough seas at the well site, 40 miles off the Louisiana coast. But the pipes are now being connected and tested, and the system is expected to start working by Sunday, collecting a few thousand barrels a day at first but eventually increasing its capacity, the admiral said.

“Somewhere between Sunday into Monday, maybe early Tuesday at the latest, we’ll probably be able to replace the amount that was being recovered by the Discoverer Enterprise and maybe exceed that,” he said.

Unlike the current cap, which is still leaking some oil and gas, the new one is designed to fit tightly and capture all of the flow from the well, estimated at 35,000 to 60,000 barrels a day. In addition to the Helix Producer, another ship will eventually be brought in to handle the oil, making four collection vessels in all.

Replacing the existing cap has been in the planning stages for weeks, and the new cap is already on the seabed, said a technician with knowledge of the effort. Removing the existing cap should be relatively straightforward, as only its weight keeps it in place on the stub of the riser, the large pipe that collapsed after the blowout and explosion April 20. The cap is connected by a pipe to the Discoverer Enterprise, which can lift it up and maneuver it out of the way fairly quickly.

Installing the new cap, by contrast, is far more complicated. Submersibles will first have to cut six bolts connecting the riser to a flange at the top of the blowout preventer. Once the last of the riser is removed, the new cap can then be placed on the flange and connected, said the technician, who spoke on condition of anonymity because he was not authorized to comment on the work.

Much like the failed blowout preventer, the new cap contains three devices that will allow technicians to completely shut off the flow of oil. Admiral Allen said this might prove useful in planning for permanently stopping the gusher and sealing the well through relief wells.

Once the cap is installed, he said, technicians will shut the valves to gauge the pressure. This will help determine whether there is any damage in the well bore, and how much heavy drilling mud will have to be pumped into the bottom of the well to permanently stop the oil.