Blow Out Preventer

Critical Components in a Complex System

After the explosion of the Deepwater Horizon oil rig, investigators focused on the failure of a component on the well's blowout preventer that is supposed to close off a well spewing out of control. The device, called a blind shear ram, is the only part of the blowout preventer that can completely seal the well. Minutes after the explosion, at least one rig worker hit an emergency button, which is supposed to trigger the blind shear ram within about 30 seconds, and then disconnect the rig from the well. But that night, the blind shear ram never fully deployed.

Inside the Blowout Preventer

The blowout preventer is a five-story structure that contains devices that allow well operators to maintain control of the well. Once oil, gas or other fluids are flowing, various components of the blowout preventer can be used to seal the space between the drill pipe and the well bore. But one of the structure's most critical roles is to stave off a disaster in a blowout — the sudden release of uncontrolled oil from the well.

Inside the Blind Shear Ram

Of all the components on the blowout preventer, only the blind shear ram was designed to shut down the well in a blowout like the one that took place on the Deepwater Horizon oil rig on April 20. It is the only device that is supposed to cut through the thick drill pipe and seal off the hole.

Unlike many other parts of the Deepwater Horizon's blowout preventer, the blind shear ram has no backup. The breakdown of any part of the ram can lead to disaster. One of the most critical components of the blind shear ram is the shuttle valve, the only point for the hydraulic fluid to enter the ram.

A risk analysis commissioned by the manufacturer of the blowout preventer identified this valve as one of the weakest links. As the fluid flows through the system, it has two possible pathways until it reaches the valve. So if the valve fails, the well will not be sealed.

HOW IT WORKS:

1. Fluid enters the shuttle valve from one of two inlet ports and pushes a metal "shuttle" to one side and flows down the stem of the T-shaped valve.
2. The fluid flows behind pistons, which drive the ram to shear the drill pipe.
3. Wedge locks slide in to prevent the pistons from moving back.
4. Rubber seals on the ram close off the well. Oil pushing up from the well adds pressure below and behind the ram, helping to keep the ram closed.