After three days of encouraging pressure tests, a senior BP official said Sunday that the company’s recently capped well in the Gulf of Mexico was holding up and that BP now hoped to keep the well closed until it could be permanently plugged. But government officials were more skeptical and cited a new potential problem.
That BP plan differs sharply from the one the company and the federal government had suggested only a day earlier, to eventually allow the flow of oil to resume temporarily, collecting it through pipes to surface ships.
If BP succeeds in keeping the cap atop the well closed until a relief well is finished, that would mean the gusher would effectively be over, three months — and tens of millions of gallons of oil — after it began. It would be a major turnaround after weeks of failure for the oil giant, which had been harshly criticized as being unprepared for such a disaster.
“We’re hopeful,” Doug Suttles, the company’s chief operating officer for exploration and production, said in a conference call with reporters Sunday morning.
“Right now we do not have a target to return the well to flow,” he said.
The federal government was more cautious, saying only that the test could be extended 24 hours at a time after scientific reviews.
Late Sunday, the government ordered BP to step up monitoring of the well after “undetermined anomalies” were discovered on the seafloor nearby.
In a letter to the company, Thad W. Allen, the retired Coast Guard admiral who commands the response to the oil spill, also noted that tests had detected a seep — usually a flow of hydrocarbons from the seafloor — “a distance from the well.”
And while the letter said the federal government would allow the test to continue for now, the discovery of a seep and the unspecified anomalies suggest that the well could be damaged and that it may have to be reopened soon to avoid making the situation worse.
The pressure testing, which began Thursday with the closing of valves on the cap and is designed to assess the condition of the well, was originally expected to last 48 hours. “We need to be careful in predicting how long it will go,” Mr. Suttles said.
If a problem crops up, he said, collection systems could be restarted, some within a few hours. In a few weeks there should be enough capacity to collect more than the high estimate of 60,000 barrels a day. But Mr. Suttles said that if valves on the cap were reopened to restart collection, oil would pour anew into the gulf for up to three days.
If the well is not reopened, it could mean that the precise volume of oil that leaked — the well has been estimated to be flowing at a rate of 35,000 to 60,000 barrels a day — may never be known. That raises the question of whether the company might escape some liability for the spill.
It has been an encouraging several days for BP, but it comes after many engineering efforts that produced little but a lexicon of strange terms, all defining failure: containment dome, junk shot and top kill among them.
Even the good news about the test and the new cap, which was installed last week, left many wondering why the project could not have happened earlier.
BP has pointed out that the concept — essentially, putting a new blowout preventer atop the existing one that failed when the Deepwater Horizon drill rig exploded on April 20, killing 11 workers — had been in the works since shortly after the disaster occurred. They have said, and diaries and other documents tend to bear out, that ideas were worked on in parallel, with those that were easier to accomplish and had a greater chance of succeeding being tried first.
In a discussion with a reporter in mid-May, Kent Wells, a senior BP vice president in charge of the subsea work, and others described in broad terms an option to install a second preventer if the top kill, in which heavy drilling mud was to be pumped into the well to stop oil and gas from coming up, did not work.
The top kill failed and one proposed explanation at the time was that the well was damaged. That put a halt, for a while, to talk of putting another blowout preventer or other tight-sealing cap on the well, out of concern that a buildup of pressure could further damage the well.
But the idea was revived, and in June BP considered using the blowout preventer from the Development Driller II rig, which was working on the second relief well, for the job. The company halted drilling of the well, aiming to bring the blowout preventer to the surface. But the federal government intervened and ordered BP to continue drilling the well as a backup in case anything went wrong with the first relief well.
The cap that was eventually used was designed and built more or less from scratch, although off-the-shelf valves and rams were used. And as with any engineering project, particularly one being conducted by remotely operated submersibles a mile underwater, installation procedures had to be devised and practiced.
That practice appeared to pay off last week when the cap was installed. It was by far the smoothest operation of the many that had been undertaken in the three-month disaster.
With the valves on the cap closed and the gulf still free of fresh oil on Sunday, Mr. Suttles said that skimming ships near the site were collecting far less oily water. Only one controlled burn was conducted Saturday, compared with 19 the day before, he said. And there were no new reports of oil reaching the shore.
“There is less and less oil to recover,” he said.
Barring bad weather, the relief well, which will be used to pump heavy mud, followed by cement, into the blown-out well to seal it permanently, may be ready by the end of July, although it may take several more weeks for the process to be completed, Mr. Suttles said.