WASHINGTON — A new theory about the origin of the blowout of a BP PLC oil well emerged on Sunday when an outside investigator said the problem could potentially be traced to cracks that formed in an underwater formation.
BP has said that the worst offshore oil spill in U.S. history started with flaws in the cement, blaming Halliburton Co. for developing a faulty cement foam that didn’t stay mixed with nitrogen. Halliburton says tests conducted before the cementing job showed that the foam was stable.
“I’d like to just maintain the possibility that one reason that the cement job may have failed was because of fracking at the time of cementing,” said Mark Zoback, a Stanford University geophysicist who serves on the National Academy of Engineering panel investigating the causes of the April 20 disaster.
The remarks, at a meeting convened at the National Academy of Engineering, undercut BP’s effort to assign blame for the April 20 Deepwater Horizon explosion to its contractors instead of its own well design.
BP had said that the foam likely failed to properly mix with the nitrogen.
“The foam system was stable,” Thomas Roth, vice president of cementing for Halliburton, told the panel. Mr. Roth also said that foam cement has “very good fluid-loss control by its basic design,” and that more than 400 hours of testing were conducted in the planning of the well. The statements challenge BP’s findings that the foam lacked fluid-loss additives and that not enough testing was conducted.
BP has said that no oil or gas entered the Macondo well before Halliburton started its cement work. BP has said that rig workers circulated 870 barrels of fluid through the well before the cement was pumped, a standard procedure that would have indicated holes or perforations in the well. BP has said that circulating fluid for too long should be avoided because that could wash dirt out of the hole and risk a bad cement job.
But Mr. Zoback zeroed in on evidence that fluid that circulated through the well leaked out, a phenomenon known as lost returns, that can signify cracks in a well.
“At a number of times in your report, conclusions are reached predicated on the statement that there were full returns during the cement job,” Mr. Zoback told Mark Bly, BP’s head of safety and operations, and other members of the BP team that prepared a report outlining what caused the April 20 disaster.
“Yet it became clear on August 25 that in fact there were 80 barrels of fluid loss during the cementing,” Mr. Zoback said. “So all of this kind of comes together in way that would suggest that…hydraulic fracturing occurred at the time of cementing. If that in fact happened, it would propagate through the analysis in a number of different ways.”
BP said that it conducted a “detailed analysis of the [fluid] losses during the cement job” and that it calculated up to three barrels of losses.
Mr. Zoback keyed in on Halliburton slides suggesting that the casing BP used did not go deep enough to overlap with the sand that would have been most susceptible to cracking. “Is then at least one possibility that one can infer from your own presentation that during cementing that that sand from below the casing actually cracked and that’s where the cement went?”
“That would be possible,” Mr. Roth said.
Halliburton did not entirely escape scrutiny. The contractor came under fire for allowing BP to proceed with developing the well even though BP had decided to use only six centralizers, which are essential to ensure that cement flows evenly throughout a well, instead of the 21 recommended by Halliburton.
“Why did you proceed?” Donald Winter, the chairman of the National Academy of Engineering panel, asked Halliburton executives. “Why didn’t you pull the red cord and say this is an unsafe operation?”
“We didn’t see it to be an unsafe operation as it was being executed,” Mr. Roth said.