Giant metal shears successfully sliced and closed pipe full of runaway crude in the early moments of last April’s Deepwater Horizon disaster, but the oil blasted through rubber gaskets around the blades and unleashed the nation’s largest spill, according to sources familiar with an ongoing investigation.
The shear ram system was a central component of the blowout preventer — a 45-ton array of valves that sat on top of the Macondo wellhead a mile beneath the surface of the Gulf of Mexico. The blowout preventer, or BOP in industry shorthand, has been the subject of a forensic examination since it was raised last year and transported to a NASA facility outside New Orleans.
A joint investigation by the Coast Guard and the Interior Department’s Bureau of Ocean Energy Management, Regulation and Enforcement is trying to determine why the device, which is supposed to seal off the well in an emergency, continued to let oil flow, contributing to the disaster that destroyed the rig, killed 11 men and started the 85-day spill.
The BOP is designed to cut and close pipe leading from a well in an emergency — either activated intentionally by a rig crew or automatically if the BOP loses power, communication and hydraulic connections to the rig.
Investigators believe the latter circumstance closed the Deepwater Horizon’s blowout preventer, although crew members tried to activate the system after an explosion rocked the rig, according to the sources.
The sources have varying connections to the investigation and requested anonymity because they aren’t authorized to discuss it.
Flow too strong?
They said the force of oil and gas flowing through the well apparently was too strong for rubber gaskets called packers that surround the edges of the shear ram blades. Erosion patterns inside the BOP suggest that the packers essentially were blown away, allowing oil to flow around the closed blades.
The conclusions — if they are part of the investigation’s final report — could increase fears that surfaced about the fallibility of blowout preventers in the days after the Deepwater Horizon blast.
Spokesmen for Trans-ocean, which owned the Deepwater Horizon; BP, which owned the well; and Cameron, which built the BOP, declined comment.
Gene Beck, a petroleum engineer and well expert who teaches at Texas A&M University, said BOP shear rams are quite capable of closing against high pressure, but as the rams close, the fluid velocity increases and can erode sealing elements.
“BOPs have a better chance of working the earlier in an event they are used because pressures and velocities will be much lower,” Beck said.
David Pursell, head of macro research at Tudor Pickering Holt & Co. in Houston, said the failure of the shear ram packers opens other questions about whether the packers were maintained properly, and whether the BOP as designed could have stopped a flowing well.
‘Time for a redesign’
“When you close your shear rams, you’re at DefCon 5. Y our well is probably flowing,” Pursell said. “If the BOP can’t hold a well at full flow, than maybe it means it’s time for a redesign.”
A number of investigations into the accident are continuing, but a presidential commission, in a recent report, identified the primary causes of the accident as a poor cement job in the well combined with a failure of the rig’s crew to recognize the signs of the imminent blowout.
Blowout preventers aren’t actually designed to stop the full force of a flowing well once it’s out of control. Rather, they’re intended as a last resort when a blowout is likely, to keep hydrocarbons from flowing up a riser pipe to the rig.
Investigators have said the Macondo well was showing signs of a blowout 45 minutes before operators on the rig took any measures to seal it.
‘Not foolproof’
Lawmakers who investigated the disaster said they were shocked last year to learn hundreds of different ways that blowout preventers considered “fail-safe” could, in fact, fail. At the time, then-House Energy and Commerce Committee Chairman Henry Waxman, D-Calif., said it was clear that blowout preventers “are not foolproof — not even close.”
‘Failure modes’
A report prepared by Transocean in 2001 documented 260 different “failure modes,” including problems with old or worn packing elements that could prevent the device from sealing around drill pipe. The document also warned that a blown seal or corrosion could cause shear rams to close incompletely and that damaged packers could cause an inability to seal the wellbore.
A 2004 study into whether BOP shear ram designs were adequate to seal wells in the more challenging deep-water environments of the Gulf of Mexico noted that shear rams tend to have less rubber in the packers than other valves on the BOP, which “… could make them more vulnerable to sealing difficulties, but generally, shear rams have completely acceptable fatigue life.”
A deep-water retrofit
Lawmakers and federal regulators have considered mandates to improve the testing and design of blowout preventers. The House passed legislation last year that would impose new requirements for redundant rams and backup control systems to boost the reliability of BOPs.
Michael Bromwich, director of the Bureau of Ocean Energy Management, Regulation and Enforcement, said in a recent interview that the agency will enact tougher BOP rules in the future, but they weren’t included in emergency regulations developed in the weeks after the spill because it was determined it could take up to two years for all deep-water rigs to retrofit their BOPs.
Dlouhy reported from Washington and Fowler from Houston. Brett Clanton in Houston contributed. Email: tom.fowler@chron.com jdlouhy@hearstdc.com.
