LOS ANGELES — Although BP's Gulf well appears to be plugged from the top and bottom, the federal spill commander said Friday that government and company officials have agreed a relief well should be completed to ensure a permanent seal.
Retired Coast Guard Adm. Thad Allen on Thursday raised the possibility that last week's "static kill" operation, in which the well's inner casing was jammed with concrete, might have made that final step unnecessary. A four-hour pressure test was conducted to figure out whether oil was still flowing freely from its deep reservoir into the outer ring of the well bore.
The readings indicated the flow had indeed been blocked by last week's cementing. "We have sealed the well at this point," Allen said Friday.
But engineers can't tell whether that bottom plug of the outer ring, called the annulus, is good and solid, or thin and flimsy.
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So they are not yet declaring victory over a well that created one of the world's largest oil spills, shut down a third of the Gulf to fishing and wiped out much of the region's summer tourist season.
"Everybody is in agreement we need to proceed with the relief well. The question is how to do that," Allen said after consulting with the head of BP, as well as the secretaries of energy and the interior.
Paradoxically, the success of the static kill has complicated the final phase of the relief well maneuver. "We probably did too good a job," Allen said.
Not only did the static kill stuff the well's casing with dense mud and concrete, it seems to have forced concrete down into the oil reservoir and back up into the base of the annulus. That has trapped what BP estimates to be 1,000 barrels of oil between the bottom and the top cap.
Scientists are worried that when the relief well pours more mud and concrete into the bottom to thoroughly seal it, the increased pressure could force the trapped oil upward, perhaps damaging the capping apparatus, or downward, breaking the bottom seal.
"What we don't want to do is somehow upset what we've already done," Allen said.
Engineers spent Friday debating how to proceed with the relief well without creating new problems. It is possible, Allen said, that they could devise some way of diffusing a pressure buildup.
"It remains a work in progress. We're trying to assess the options we have," Allen said.