BP Installs New Well Cap

In this image from a video provided by BP, deep-sea robot lowers a containment cap onto the site of the Deepwater Horizon oil spill. BP-AP

[This story was updated at 10 p.m. ET on July 12.]

After days of preparation, BP's effort to replace the loose-fitting cap that has been collecting oil for the last few weeks with a sealing cap appears to have gone successfully. On Monday evening, the cap was installed over the gushing well, raising hopes that the company will be able to either seal off the well entirely, ending the leak, or at least to contain all of the flow over the next few weeks by sending it upward to several surface collection vessels.

Over the last few days, engineers and technicians removed the old cap, unbolted the cut-off riser pipe from a flange at the top of the blowout preventer, and bolted on a new specially designed pipe in its place. Unlike the previous cap, a simple structure that sat on top of the cut-off riser and funneled oil to a surface ship, the new cap is a monstrous and complex 18-foot-tall device that weighs upwards of 75 tons. Called a "three-ram stack," the new cap resembles a mini–blowout preventer, with hydraulic valves that should be strong enough to hold back the oil flow entirely.

With the cap attached, BP next will will temporarily "shut in" the well to take pressure measurements that will be used by oil-industry and government scientists to determine a suitable long-term containment plan. The test will involve fully closing the valves on the new cap and discontinuing collection of oil from the blowout preventer (currently, the Q4000 vessel and the Helix Producer are drawing oil up to the surface from the choke and kill lines of the blowout preventer). At this point the full force of the oil gusher will be pressing up against the new cap, which contains sensors that will collect pressure data to allow scientists to determine whether the well bore is structurally intact or if it has been compromised. "We need to make sure that the flow can't come around the well bore rather than through the well bore," Suttles said. The test is expected to start sometime Tuesday.

Click to view a timeline of the gulf oil spill Gerald Herbert

High pressure would be good news, suggesting that the well casing is undamaged and that all of the flow is coming up through the well. In this scenario, it would be possible to keep the well closed off indefinitely, effectively ending the spill (the relief wells would still be completed to permanently seal the well with cement). Low pressure, on the other hand, would be very bad, suggesting that oil is leaking out deep underground, through damaged sections of the well casing, and percolating into the surrounding rock. In a worst-case scenario, that oil could find its way up to the surface and start an uncontrolled leak from somewhere on the floor of the gulf. Either way, a low-pressure result would force engineers to open the valves and allow oil to flow once more, though BP says it would soon have enough capacity to funnel all of it to the surface for collection.

Even if the test results are grim, at least there'll soon be some empirical data on the state of the well bore, something that has been much needed but long lacking.