![]() ![]() The circular wedge then forces the sealing element toward the inside. Hydraulic pressure is applied to the low side of a wedge-shaped piston. The operating principle of this type of preventer is simple. ![]() Drilling mud or water can be used for lubrication. Still, it is necessary to lubricate the pipe while stripping it into the well. The pressure can also be adjusted to ease the passage of the tubular while stripping into the well by reducing friction. Operating pressure is generally lower than that used for ram-type preventers because the piston area is far larger. Because of its variable diameter, it also allows tool joints to pass when the pipe is being lowered into the hole while surface pressure is present, an operation called stripping (check also well control stripping procedure) (overcoming the pressure area forces with the pipe weight) or snubbing (forcing the pipe into the hole because the weight is not enough to overcome the pressure area forces) (Fig.6). This means that it can also seal around kelly (hexagonal shapes are better than square shapes). This type of preventer is able to seal around any object with a circular (or nearly circular) cross-section as well as over an empty hole. BOP Blowout Preventers Types Annular Preventers Type Even after setting multiple casings (with each casing head adding to the total height of the equipment), it still must be possible to accommodate the full preventer stack. ![]() An important consideration for the design of the BOP blowout preventer stack arrangement is the space it occupies under the rig. ![]()
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