This is the first time since the Deepwater Horizon drilling platform exploded and sank in April that no oil is flowing from the damaged wellhead.
However, the event is not cause for celebration. BP officials say that the halt in the flow was to be expected while the company conducts tests on the new containment cap it installed over the wellhead earlier this week. The tests, which the company is running to determine not only the security of the containment cap but also the condition of the well bore itself, are expected to run from 6 to 48 hours.
BP hopes that the pressure at the cap will continue to rise steadily throughout the test period. If that happens, it will indicate that the cap has contained the spill and that no oil is seeping or leaking from the well bore. Should the pressure rise unevenly, not rise at all, or rise, then fall, it could signal that oil is escaping into the Gulf through other openings. That in turn would make final sealing of the damaged well more difficult at the least.
Drilling of relief wells in the area has been halted while the tests proceed. Once the tests are concluded, drilling will resume. The containment cap is only a temporary measure to halt the flow of oil; to ensure that no more oil flows from the well, it must be plugged. Once the relief wells are complete, the damaged bore will be filled with heavy driling mud and sealed with cement, which should bring a permanent end to the worst oil spill in U.S. history.