BP's investigation finds series of failures in Macondo blowout

Sept. 13, 2010
BP PLC, operator of the Macondo well in the Gulf of Mexico, said a series of failures, both mechanical and human, made by "multiple companies" contributed to the well's blowout and subsequent fire and explosion on Transocean Ltd.'s Deepwater Horizon semisubmersible.

BP PLC, operator of the Macondo well in the Gulf of Mexico, said a series of failures, both mechanical and human, made by "multiple companies" contributed to the well's blowout and subsequent fire and explosion on Transocean Ltd.'s Deepwater Horizon semisubmersible.

"To put it simply, there was a bad cement job and a failure of the shoe track barrier at the bottom of the well, which let hydrocarbons from the reservoir into the production casing," said Tony Hayward, BP's outgoing chief executive. "The negative pressure test was accepted when it should not have been, there were failures in well-control procedures and in the blowout preventer, and the rig's fire and gas system did not prevent ignition."

The Apr. 20 explosion and fire killed 11 people. The semi sank on Apr. 22, resulting in a massive oil spill in the gulf. Multiple US government investigations are ongoing.

BP released its own investigation report Sept. 8 based on a 4-month investigation led by Mark Bly, BP's head of safety and operations, and conducted independently by a team of more than 50 technical and other specialists drawn from inside BP.

Bly emphasized during a briefing on Sept. 8 in Washington, DC, where BP formally released the report, that it was not an effort by the company to place blame for the well blowout and rig explosion. "We work for BP, but it was a completely independent process," Bly told reporters. "We were given complete license to investigate as we saw fit. We were critical of ourselves as well as others, and hope this independent approach builds understanding about what happened."

Limited focus

The investigation concentrated on events leading up to the accident and did not attempt to address the subsequent oil spill into the gulf or efforts to stop the leaks, Bly explained. It used real-time data from the well to suggest what might have occurred, but had limited access to witnesses and information from Transocean, which owned the Deepwater Horizon semi; Halliburton Co., which provided cementing services; and other service and supply companies, Bly said.

The damaged blowout preventer (BOP), along with the lower marine riser package, was removed Sept. 4 from the Macondo well in the deepwater Gulf of Mexico and lifted on board the Q4000 multiservice vessel. The BOP is considered evidentiary material, and is now under the supervision of the Deepwater Horizon Criminal Investigation Team and FBI Evidence Recovery Team. Photo by PO1 Thomas M. Blue, US Coast Guard.

"We were not about apportioning fault or blame," he maintained. "Our work may be used for those purposes, but that wasn't what we were about. We wanted to find out what happened."

The Macondo oil and natural gas exploration well on Mississippi Canyon Block 252 was drilled to 18,360 ft in 4,992 ft of water. It penetrated a Miocene reservoir and was deemed a commercial discovery. BP planned to temporarily abandon the well for later completion as a production well.

At the time of the blowout, crews had run a final string of casing and put a cement barrier in place to isolate the hydrocarbon zones. Integrity tests were done, and the top 8,367 ft of mud was being circulated out using seawater.

"The remaining steps were to set a cement plug in the casing and to install a lockdown sleeve on the casing hanger seal assembly," before disconnecting the BOP and suspending the well, BP said.

Report's conclusions

The report, which runs nearly 200 pages, came to the following conclusions:

• The cement slurry that was used and the shoe track barriers at the bottom of the Macondo well failed to contain hydrocarbons within the reservoir, as they were designed to do, and allowed gas and liquids to flow up the production casing.

• Negative pressure test results were incorrectly accepted by BP and Transocean, although well integrity had not been established.

• Transocean's Deepwater Horizon crew failed to recognize and act on an influx of hydrocarbons into the well for 40 min until the hydrocarbons were in the riser and rapidly flowing to the surface.

• After hydrocarbons reached the semi, the flow was routed to a mud-gas separator, which vented gas directly on the rig rather than diverting it overboard.

• Gas flowed into the semi's engine rooms through the ventilation system and created a potential for ignition that the semi's fire and gas system did not prevent.

• Even after explosion and fire had disabled its crew-operated controls, the semi's BOP on the seabed failed to automatically activate to seal the well, probably because critical components were not working.

"Based on the report, it would appear unlikely that the well design contributed to the incident, as the investigation found that the hydrocarbons flowed up the production casing through the bottom of the well," Hayward said.

BP's incoming Chief Executive Bob Dudley noted the accident was "a shared responsibility among many entities." He said BP was determined to learn lessons and will launch a broad review to improve the safety of its operations.

"We will invest whatever it takes to achieve that," Dudley said. "It will be incumbent on everyone at BP to embrace and implement the changes necessary to ensure that a tragedy like this can never happen again."

Responding to BP's findings and recommendations, a Transocean spokesman called it "a self-serving report that attempts to conceal the critical factor that set the stage for the Macondo incident: BP's fatally flawed well design."

The spokesman said the well operator made a series of cost-saving decisions that increased risk, including using a long production string instead of a casing tie-back, which decreased the number of gas flow barriers; neglecting to run a cement bond log to test the cement's integrity; installing fewer than one third of the recommended number of centralizers, which increased the risk of cement channeling and gas flow; failing to conduct a complete bottoms-up circulation of the well to insure the cement seal's quality; and not running a lockdown sleeve to secure the production string to the wellhead, eliminating yet another blowout barrier.

Distractions possible

Bly suggested, however, that human error also may have been responsible, particularly since the well was being temporarily shut down and the rig disconnected prior to its moving to another job, and employees may have been distracted by other tasks. "The plan was to use 6 centralizers originally and 15 subsequently," he said. "The additional centralizers were on board, but the crew incorrectly thought they were the wrong kind and would have posed a greater risk." The presence of several visiting BP executives probably did not play a role since this occurred frequently, he added.

"We don't know why they made the decisions," said James Weatherby, a BP safety official who was not part of the investigation but consulted with participants. "We believe their actions made sense to them at the time. That's why we recommended more attention to operating practices."

Kent Corser, a BP drilling manager who was part of the investigation team, said at the Washington briefing that the well's design had no bearing because it was used without any problems on 58% of the other deepwater wells in the gulf. "This is a robust design, with heavy-duty casing and a long string," he said.

Bly said BP relied on Halliburton, as the cementing contractor, for advice on whether to conduct a cement bond test to assure that the mixture would hold. "What we saw, when we went through the data more closely, was that other attributes should have been considered more closely," he said. "Halliburton should have done this, and BP should have required it."

A Halliburton spokeswoman told OGJ by e-mail that the company "remains confident that all the work it performed with respect to the Macondo well was completed in accordance with BP's specifications for its well construction plan and instructions, and that it is fully indemnified under its contract for any of the allegations contained in the report."

BP's investigation team proposed 25 recommendations regarding BOPs, well control, pressure-testing for well integrity, emergency systems, cement testing, rig audit and verification, and personnel competence.

The company said it expected a number of the investigation report's findings to be considered relevant to the oil industry more generally and for some of the recommendations to be widely adopted.

BP said the report was based on information available to the investigating team. It noted that additional relevant information may be forthcoming, for example, when Halliburton's samples of the cement used in the well are released for testing and when the Deepwater Horizon BOP is fully examined now that it has been recovered from the seabed (OGJ Online, Sept. 5, 2010).

Cement analyzed

The investigation team found hydrocarbons entered the well after the cement job, which was conducted by Halliburton. BP's investigation team assessed the cement slurry design, cement placement, and to examine the process used to confirm the cement placement.

A third-party cementing laboratory concluded the foam cement slurry used for the Macondo well was likely unstable, resulting in nitrogen breakout. CSI Technologies conducted tests to match as closely as possible the actual slurry used. The investigation team did not have access to the Halliburton cement and additives used for the Macondo job.

"The results of these test indicate it was not possible to generate a stable nitrified foam cement slurry with greater than 50% nitrogen (by volume) at the 1,000 psi injection pressure," the report said. "For the Macondo well, a mixture of 55-60% nitrogen was required at 1,000 psi injection pressure to achieve the design mixture of 18-19% nitrogen foam cement at downhole pressure and downhole temperature conditions."

BP's investigation team also found the rig crew and well site leaders misinterpreted a negative-pressure test result that indicated well integrity was not established, but the well site leaders and rig crew failed to recognize this or to remedy the situation.

BOP failure

The explosion and fire very likely damaged multiplex cables, disabling emergency systems from closing the blind shear ram (BSR) within the BOP. The damaged cables prevented an emergency disconnect sequence (EDS) signal from telling the BSR to cut the drill pipe and seal the wellbore, BP's report said.

Two independent control pods on the BOP are supposed to initiate an automatic mode function (AMF) to close the BSR if electric power, communications, and hydraulic power are all lost. But both the blue and yellow control pods from the Deepwater Horizon BOP had problems.

An insufficient charge was discovered on a battery bank in the blue pod, and a failed solenoid valve was found in the yellow pod.

"If these conditions existed at the time of the accident, neither pod would have been capable of completing an AMF sequence," the report said. Both pods were retrieved after the accident.

"A review of BOP maintenance and testing records provided by Transocean indicated instances of an ineffective maintenance management system for Deepwater Horizon," the report said, noting batteries in the blue pod were fully depleted when the BOP was brought to the surface in December 2007.

Cameron, which manufactured the BOP, reported a nonoriginal equipment manufacturer (non-OEM) part was found on the yellow pod, BP's investigation team said.

"The BOP maintenance records were not accurately reported in the maintenance management system," BP's report said. "The condition of critical components in the yellow and blue pods, and the use of a non-OEM part, which were discovered after the pods were recovered, suggest the lack of a robust Transocean maintenance management system for Deepwater Horizon BOP."

Drill pipe status

National Incident Commander and retired US Coast Guard Adm. Thad Allen has reported two pieces of drill pipe inside the BOP as well as a long section of drill pipe going from the BOP into the well.

BP's report said geometric analysis was undertaken to determine the status of drill pipe in the riser and across the BOP.

"The investigation team has concluded that the left-hand pipe in the riser kink section is likely the portion of the drill pipe (from above the eroded point), which broke off and fell down the riser when the top drive fell onto the rig floor or as the rig sank, and the riser collapsed," the report said.

A right-hand pipe section appeared to have erosion that could have happened when it was in the BOP, BP's report said, noting the right-hand pipe is believed to have moved by 25 ft, which could have happened when the semi drifted after power was lost.

At BP's Washington briefing, Fereidoun Abbasian, a vice-president of drilling and completion technology at BP America and an investigation team member, said it appeared likely that one piece of 5½-in. pipe or debris was across the BOP's BSR when attempts were made to activate it.

The device also could have had insufficient hydraulic pressure from leaks in its system because rapidly increasing pressure may have caused its seals to deteriorate, he added. More definite conclusions are likely now that the BOP has been recovered and detailed examinations can be conducted, he said.

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