Double Blowout Preventer

[Airbrush]

Why have we not heard anything about building deep-sea oil valves with double or triple redundant blowout preventers? Then all the blowout preventers should be periodically tested. Duhhhhh!

[cypress]

The traditional subsea stack includes two blowout preventers of different designs. Each BOP is typically double redundant. They are tested at each new location and once a month.

[Airbrush]

Thanks for the reply Cypress. Do you have some experience in this field? So what happened with the Deep Water Horizons? If it had double BOP, and each is double redundant, and all tested monthly. Why did all 4 fail?

[cypress]

I am working in Deepwater Technology Deployment for an E&P company, not BP though. Our group focuses on providing our project groups with systems, designs and processes indended to prevent what happened at Macondo so we are watching this closely. I have supported Drilling and Completion Operations in the past though not currently. The top BOP is an annulus BOP that is designed to hold back moddest pressures to prevent the well control fluid and high density mud from being pushed out of the well by a "gas kick" while drill pipe is in the well. If a gas kick is not noticed in time, then the annulus BOP quickly becomes inneffective.

 

In the case of the Macondo well, gas broke out the backside of the production casing and into the well due to a failed cement procedure most likely due to poor design and process decisions by BP engineering managers. The gas quickly forced a significant amount of well control fluid out of the well and wellhead pressures rose beyond the ability of the annulus BOP before the immediate problem was realized. The ram BOP is designed to shear off the drill pipe, and it was tripped but it failed to shear off what was obstructing the BOP. There is speculation that the production casing was driven back up into the BOP by the gas kick and it prevented the shears from functioning. A design decision was made to forego use of a casing ring lock that is intended to prevented upward casing travel and a casing seal that would have prevented flow up the backside.

 

In addition the BOP tests did uncover a couple minor failures of portions of the backup deployment controls, but project managers chose to move forward without making repairs to the BOP. It is unlikely that this had a significant impact but you never know.

 

BOP's will function if the system is properly designed and all the prior conditions are met necessary to allow them to function. In the case of the Macondo well, design and process issues were the root drivers and the BOP's cannot substitute for poor decisions.

[Airbrush]

Nice explanation. Thanks for the info.