BP spill: Lists reveal what is known, what could have happened
Two documents were released May 12 at the hearing held by the US Oversight and Investigations subcommittee to inquire into the Deepwater Horizon Gulf Coast oil spill.
By OGJ editors
HOUSTON, May 14 -- Two documents were released May 12 at the hearing held by the US Oversight and Investigations subcommittee to inquire into the Deepwater Horizon Gulf Coast oil spill. These lists, entitled “What We Know” and “What Could Have Happened,” are reproduced below.
What We Know
• Before, during, or after the cement job, an undetected influx of hydrocarbons entered the wellbore.
• The 9-7/8-in. casing was tested, the 9-7/8-in. casing hanger packoff was set and tested, and the entire system was tested.
• After 16½ hr waiting on cement, a test was performed on the wellbore below the blowout preventer (BOP).
• During this test, 1,400 psi was observed on the drill pipe while 0 psi was observed on on the kill and the choke lines.
• Following the test, hydrocarbons were unknowingly circulated to surface while displacing the riser with seawater.
• As hydrocarbons rose to the surface, they expanded, further reducing the hydrostatic pressure. The well flowed and witness accounts suggest that the annular preventer in the BOP and the diverter were activated.
• An explosion occurred, followed by a power failure.
• Witness accounts that the emergency disconnect system was activated.
• The rig was evacuated.
• The BOP system failed to work as intended. Flow was not contained and the lower marine riser package did not disconnect.
• Modification have been discovered in the BOP system.
• Leaks have been discovered in the BOP hydraulics system.
• BP launched an investigation, which is ongoing.
• Cementing—design and execution.
• Casing—design and installation.
• Casing hanger—design and installation.
• BOP—configuration, maintenance, and operation.
• Well control practices.
What Could Have Happened
1. Before or during the cement job, an influx of hydrocarbon enters the wellbore.
2. Influx is circulated during cement job to wellhead and BOP.
3. 9-7/8-in. casing hanger packoff set and positively tested to 6,500 psi.
4. After 16½ hr waiting on cement, a negative test performed on wellbore below BOP. (~1,400 psi differential pressure on 9-7/8-in. casing hanger packoff and ~2,350 psi on double-valve float collar)
5. Packoff leaks allowing hydrocarbon to enter wellbore below BOP. 1,400 psi shut in pressure observed on drill pipe (no flow or pressure observed on kill line).
6. Hydrocarbon below BOP is unknowingly circulated to surface while finishing displacing the riser.
7. As hydrocarbon rises to surface, gas break out of solution further reduces hydrostatic pressure in well. Well begin to flow, BOPs and emergency disconnect system (EDS) activated but failed.
8. Packoff continues to leak allowing further influx from bottom.