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Workers misread key test before Gulf rig accident

 * Key pressure test misinterpreted by rig workers-BP
 * Cementing failed at some point-BP
 WASHINGTON, May 26 (Reuters) - Workers on the ill-fated
Deepwater Horizon rig misinterpreted a key test indicating a
critical problem with the operation in the hours before the
explosion that led to the massive Gulf oil spill, BP BP.L
officials said on Wednesday.
 A negative pressure test performed on the day of the
explosion showed pressure on the drill pipe was at 1,400 lbs
per square inch, said BP officials helping to complete the
company's internal investigation of the accident.
 During this same period, the rig's kill line data showed
basically no pressure. The workers seem to have interpreted
these results to mean the pressure test was successful and that
no hydrocarbons could enter the well, said officials. Some of
these investigators declined to be identified because of
sensitive nature of the accident.
 "This is, we believe, where a mistake was made," an
official told reporters at a press briefing. "Looking at the
information suggests the negative tests in fact failed."
 Some details about why key decisions were made may never be
known because some of those involved did not survive the
accident, the officials said.
 "The integrity testing that was done was not understood by
the people on the rig. They believed they had achieved
isolation from the reservoir, when indeed it hadn't been
achieved," said Mark Bly, BP group head of safety and
operations.
 BP briefed reporters on the details of their investigation
so far after releasing this initial report to lawmakers earlier
this week. [ID:nN26010464]
 The officials said pressure should have measured the same
on both the drill pipe and kill pipe.
 The officials refused to identify who was responsible for
the decision to move forward with finishing the well. The rig
was owned an operated by Transocean RIGN.S, but was leased by
BP.
 Eventually workers recognized there was a problem on rig
and shut down the pump, but it was not enough to prevent the
explosion.
 Both BP and Transocean have lobbied blame at each other
since the accident. The rig's chief mechanic told federal
investigators on Wednesday that there was a "skirmish" between
BP and Transocean staff about whether to proceed with a
procedure that may have been a fundamental mistake that led to
the explosion. [ID:nN26206690]
 In addition to the misread test, the investigators said the
cementing on the well must have failed at some point to
completely plug the well. Some cementing on the rig was
completed by Halliburton HAL.N. Halliburton has defended its
work, saying that all of its cementing procedures were dictated
by BP.
  (Reporting by Ayesha Rascoe; Editing by Lisa Shumaker)






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