Federal investigators probing the blowout that led to the Gulf oil spill grilled a Halliburton official Tuesday about concerns the petroleum services firm raised over the potential for a severe gas flow problem if a BP plan was used.

Halliburton and BP were at odds over a key device, known as a centralizer, that is used as part of the process to plug a deepwater well like the oil giant was doing at the time of the disaster. Halliburton's well design expert testified he told BP officials April 15 — five days before the well blew — that fewer centralizers would cause a bigger gas flow problem.

Centralizers are meant to ensure casing runs down the center of the well bore. If casing strings are cemented off-center, there is a risk that a channel of drilling fluid or contaminated cement will be left where the casing contacts the oil formation, creating an imperfect seal.

BP rejected Halliburton's recommendation to use 21 centralizers. Instead, BP used six centralizers.

The April 20 blowout of BP's undersea well, which killed 11 workers and caused 206 million gallons of oil to spew, was triggered by a bubble of methane gas that escaped from the well and shot up the drill column, expanding quickly as it burst through several seals and barriers before exploding, according to interviews with rig workers conducted during BP's internal investigation and obtained by The Associated Press in May.

E-mails released by Congress in June show that a BP engineering official conveyed Halliburton's conclusions to a BP well team leader and his own concerns that BP needed to install the extra centralizers. The well team leader responded he didn't like the idea because it would take 10 hours to install them.

"BP then in turn decided not to run the additional centralizers without consulting me or their in-house specialists," Jesse Gagliano, the Halliburton official, told members of the joint U.S. Coast Guard-Bureau of Energy Management, Regulation and Enforcement investigative panel.

Tuesday's testimony was part of the panel's fourth session of hearings aimed at determining the cause of the explosion and how regulation, safety and oversight can be improved.

After answering questions posed by the Coast Guard and other panel members, Gagliano was grilled by attorneys representing some of the other parties involved, including BP. The oil giant's attorney often took on a sarcastic tone, repeating questions and responding with disbelief at times to Gagliano's answers.

Gagliano was asked to read the e-mail he received April 20, about three hours before the well blew out, from Halliburton's engineer on board the rig. "We have completed the job and it went well," the rig-bound engineer wrote to Gagliano. The attorney noted the engineer made no reference to gas flow problems or BP's decision to use fewer centralizers.

Pointing to another 12-page document, prepared by Gagliano, the attorney asked if it reflected his "best engineering judgment and analysis."

"No, this reflects what was actually pumped," Gagliano answered. "No, my best engineering analysis would have been to run 21 centralizers."

In addition to operating the Deepwater Horizon rig that exploded, BP owned a majority interest in the ruptured undersea well. Transocean Ltd. owned the rig. Anadarko Petroleum held a minority interest in the well.

The documents released in June include a series of e-mail exchanges between BP well team leader John Guide and BP drilling engineering team leader Gregory Walz. In an April 16 e-mail, Walz said he had located an additional 15 centralizers in Houston and could fly them out to the Deepwater Horizon.

Suggesting he knew he would get some resistance, Walz added: "I do not like or want to disrupt your operations and I am a full believer that the rig needs only one team leader. I know the planning has been lagging behind the operations and I have to turn that around. I apologize if I have over step my bounds."

Later the same day, Guide panned the idea in part because of the time it would take to install the extra centralizers. "I do not like this," Guide wrote in an e-mail to Walz.

Nathaniel Chaisson, a Halliburton cementer who was on the rig assisting with the job, said he saw the additional centralizers on board the rig, but BP still decided against using them.

Also Tuesday, a Transocean official said a high-ranking employee indicated a pressure test problem had been resolved hours before BP's Gulf of Mexico well blew out.

Daun Winslow told the government panel that there was confusion among workers in the drill shack, who were talking before the explosion about a negative pressure test, a procedure typically done before a well is plugged. Later in his testimony, Winslow backtracked, saying instead he would characterize what was happening in the room as a "discussion" rather than confusion.

Winslow said he left while the drill team and tool pushers were discussing the pressure test to avoid disturbing them. He said the highest-ranking Transocean person on the rig later gave him a "thumbs up," indicating it had been resolved.

BP drilling engineer Brian Morel invoked his constitutional right not to answer questions before the panel Tuesday.


Weber reported from New Orleans.