Blow Out Preventer Detail
BP technical briefing and update on Gulf of Mexico oil spill 10 May 2010
Failure of the Large Dome:
A lot more gas involved in leak than previously believed.
Moving to a smaller dome because there will be less seawater in it and less likely to hydrate formation. Methanol injection to aid deployment of the small dome. Small Top Hat is about the size of a barrel and sucks up the oil.
What was the failure of the Large Dome and the top hat. Is there detail of the hydrate formation of the top hat?
A: Quantity of hydrate is greater than they were able to cool with the warm water being pumped down. Appears to be too many hydrates. Use this to help block the leak. Hydrates were real failure of the containment dome.
Top hat was a coffer dome according to BP. It was a 40ft tall and weighed 78 ton. It failed when the top of the dome filled with ice and blocked the flow. The hole at the top was 12″. They were in the process of connecting the pipe to the surface piping lined with warm sea water when the hydrates at the top froze and blocked the flow. The dome became too buoyant to form a watertight seal against the sea floor and permitted the oil to spill out around it. The spewing oil is a gassier flow than anticipated. The thought behind the smaller top hat is that keep water away from the gas and the hydrates can’t form. Pump methanol into it to prevent the hydrates.
Use the frozen water hydrates to stop the flow. Inject methane hydrates into the BOP to stop flow along with junk shot.
Water is 30 ºF at the sea floor.
1. Junk Shot and Top Kill: Junk into choke valve, mud down kill valve to reduce hydrostatic head down, and fill it with cement.
2. Remove the riser and swing in another BOP
3. Swing across a valve.
Risk of Relief Well Not Working:
Drilling two relief wells. They have to intersect a 7 inch well bore. This is not easy, though has been done before. Q: Is the second well a backup plan?
A: Yes, as a backup for the first well. Pump in mud to kill the well and then fill it with cement.
No Plan D: Hayward, “Relief wells will ultimately be successful.”
Background of top hat and junk shot options
#1 priority is how do we shut the stop off. Incredibly complicated because the BOP failed.