Primary well control barrier
During normal drilling operation it will always be the hydrostatic pressure of the drilling fluid that creates the primary barrier to avoid any flow of formation fluid into the well bore. If for any reason the primary barrier is lost the well control equipment together with the drilling fluid in the well bore will be the secondary barrier. This will allow us to re-establish the primary barrier on a safe and efficient way.
Secondary well control barrier
The well control equipment must be able to close and secure the well under all circumstances. Further to that circulation of heavy drilling fluid into the well bore and formation fluid out of the well bore under controlled manner must be possible.
The well control equipment should be able to close on open hole, meaning without tubular, around the bottom hole assembly, BHA for short, and other tubular used in the drilling operation. It should also be able to cut the drill string or lighter tubular and seal the well bore and allow the drill string to be hanged off on the pipe rams or stripped into the well bore.
To avoid single components to create total failure of the system a contingency, i.e. back up function should be built into the system.
All well control equipment must be maintained, function- and pressure tested according to company policy and procedures to assured correct function and integrity when required.
With the well closed in and the drill string in the well bore, formation pressure can be obtained through the drill string by adding shut-in drill pipe pressure, or SIDPP, with pressure hydrostatic.
To secure the drill string and obtain integrity following barriers can be used:
• FOSV, standing for the full opening safety valve,
• One way valves (IBOP, Dart sub),
• Check valves (Drill pipe floats).
To secure the annulus and obtain integrity following barriers can be used:
• Annular Preventer,
• Ram Preventer,
• Shear/Blind Ram,
• Rotating head.
During normal drilling operation two barriers must always be in place where the hydrostatic head of the drilling fluid is one and the BOP’s the other