BOP is the most important well control device, which plays an important role in drilling, especially in underbalanced drilling. The purpose of designing BOP is to close the wellbore under pressure, maintain continuous control of the well, and circulate the formation fluid entering the well.
Hydraulic BOP mainly includes two forms: gate BOP and annular BOP. Gate BOP mainly consists of shell, side door, oil cylinder, cylinder head, piston, piston rod, locking shaft, seal, gate, etc. Its working process is to use hydraulic pressure to push the piston to drive the gate to close or open, thereby closing or opening the wellhead to achieve the purpose of sealing and opening the well.
The gate of the gate BOP can be divided into four types: full seal, semi-seal, variable diameter and shear gate, which are used to achieve well sealing under different conditions. The semi-seal gate can seal the corresponding drill pipe and tubing and other pipes, and can also hang the drilling tool when necessary. When there is no pipe in the well, the full seal gate can fully seal the wellhead. In special cases, the shear gate can cut off the drilling tool. In addition, the flange outlet on the side of the shell can be used for drilling fluid circulation and throttling well killing operations.
The types of annular blowout preventers can be divided into conical annular blowout preventers and spherical annular blowout preventers according to the shape of their sealing rubber core. Their structure mainly consists of four parts: shell, top cover, rubber core and piston. When there are drilling tools, oil pipes or casings in the well, the annular blowout preventer can use a rubber core to seal annular spaces of various sizes. When there are no drilling tools in the well, it can fully seal the wellhead. During drilling, coring, logging and other operations, it can also seal the annular space formed by square drill pipes, coring tools, cables and steel wires and the wellbore. When using a pressure reducing and regulating valve, the drilling tools can be forcibly lifted and lowered through the drill pipe.
The two types of annular blowout preventers have similar working principles. When a well blowout is detected and the well needs to be sealed, the high-pressure oil supplied from the control system enters the closing chamber at the bottom of the piston from the lower oil port to push the piston upward. The spherical rubber core moves upward along the spherical surface, and the conical rubber core moves toward the center under the restriction of the top cover and the extrusion of the inner cone of the piston, tightening and embracing the drilling tool to seal the drilling tool or fully seal the wellhead. When opening the well, the piston moves downward, and the rubber core resets under the action of its own elastic force to open the wellhead.
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