Senior Staff Writer
Federal officials have released a two-volume report from Det Norske Veritas (DNV) on the forensic examination of the Deepwater Horizon blowout preventer (BOP), and the report recommends additional study be done on the BOP's mobility to fully close and seal the Macondo well.
On Apr. 20, 2010, a blowout of the Macondo well in about 5,000 ft of water off Louisiana resulted in explosions and fires killing 11 crew members on Transocean Ltd.'s Deepwater Horizon semisubmersible drilling rig. BP PLC operated the Macondo well. A massive oil spill resulted in the Gulf of Mexico.
The Bureau of Ocean Energy Management, Regulation, and Enforcement/US Coast Guard Joint Investigation Team released DNV's report on the BOP, which concluded that off-centered drill pipe prevented the blind shear rams (BSR) from fully closing and sealing the wellbore.
Transocean said, "The findings confirm that the BOP was in proper operating condition and functioned as designed. These results are consistent with the function and pressure tests conducted on the BOP in the days preceding the Macondo well blowout. High-pressure flow from the well created conditions that exceeded the scope of [the] BOP's design parameters."
While releasing the report, BOEMRE announced a seventh session of public hearings starting Apr. 4 in New Orleans. The hearings will focus specifically on the BOP forensic examination. The forensic examination is one aspect of an investigation into the accident and subsequent oil spill. The full investigation report is not expected to be released until sometime this summer, BOEMRE said.
The report said forces from the flow of the well induced the drill pipe to buckle between the upper annular and the upper variable bore rams (VBR). The drill pipe deflected until it contacted the wellbore just above the BSR.
"This condition would have most likely occurred from the moment the well began flowing and would have remained until either the end conditions changed (change in upper annular or upper VBR state) or the deflected drill pipe was physically altered (sheared)," the report said. "The portion of the drill pipe located between the shearing blade surfaces of the BSRs was off center and held in this position by buckling forces." Drill pipe became trapped between the ram block faces, preventing the blocks from fully closing and sealing.
"This position of the drill pipe between the upper annular and the upper VBRs led to buckling and bowing of the drill pipe within the wellbore," the report said.
The BOP examination was completed after the BOP stack was raised from the sea floor on Sept. 4 and transferred to the NASA-Michoud complex in New Orleans. The blind shear, casing shear, and three sets of VBR were removed from the lower section of the BOP and examined both visually and using laser profilometry. DNV used high-definition video cameras and laser profilometry in its examination.
Eight segments of drill pipe were recovered, examined, and tested. Two drill pipe segments were recovered from the BOP at Michoud. Three additional segments were recovered from the drilling riser at Michoud. Investigators also examined three other segments of drill pipe that had been previously recovered.
Function testing of the AMF/Deadman autoshear indicated the voltage of the 27-v battery in the blue pod was insufficient to activate the higher-pressure BSR pilot solenoid mounted on the blue pod. Tests of the yellow pod BSR pilot solenoid circuits were inconsistent, the report said.
DNV recommends that industry examine and study potential conditions that could arise in the event of the loss of well control. It suggests numerous studies including:
• Effects of the flow of the well fluids on BOP components and various tubulars that might be present.
• Effects that could arise from the tubulars being fixed or constrained within the components of a BOP.
• Ability of the BOP components to complete their intended design or function under these conditions.
DNV also recommended industry study the ability of shear rams to completely cut tubulars and seal the well regardless of the tubulars position within the wellbore.
"The findings of these studies should be considered and addressed in the design of future BOPs and the need for modifying current BOPs to address these findings," the report said.
DNV also recommended industry examine and study the potential effects that closing of the annulars or closing of the VBRs could have on the BOP stack, including an evaluation of how elastic buckling of tubulars could adversely affect the ability to regain control of the well.