Blowout Preventer (BOP) Equipment

The blowout preventer (BOP) equipment is the equipment which is used to shut in a well and circulate out an influx if it occurs. Blowout preventer The main components of this equipment are the blowout preventer or BOP’s. These are valves which can be used to close off the well at surface. In addition to the BOP’s the BOP equipment refers to the auxiliary equipment required to control the flow of the formation fluids
and circulate the kick out safely. There are 2 basic types of blowout preventer used for closing in a well:
Annular (bag type) or
Ram type.
It is very rare for only one blowout preventer to be used on a well. Two, three or more blowout prevention are generally stacked up, one on top of the other to make up a BOP stack. This provides greater safety and flexibility in the well control operation. For example: the additional BOPs provide redundancy should one piece of equipment fail; and the different types of ram (see below) provide the capability to close the well whether there is drill pipe in the well or not. When drilling from a floating vessel the BOP stack design is further complicated and will be dealt with later.

Annular Blowout Preventer

The main component of the annular BOP is a high tensile strength, circular rubber packing unit. The rubber is moulded around a series of metal ribs. The packing unit can be compressed inwards against drill pipe by a piston, operated by hydraulic power.  The advantage of such a well control device is that the packing element will close off around any size or shape of pipe. An annular preventer will also allow the pipe to be stripped in (run into the well whilst containing annulus pressure) and out and rotated, although its service life is much reduced by these operations. The rubber packing element should be frequently inspected for wear and is easily replaced.

The annular preventer provides an effective pressure seal (2000 or 5000 psi) and is usually the first BOP to be used when closing in a well Picture annular blow out prevention bellow. The closing mechanism is described in annular preventer bellow.

Blowout Preventer Annular BOP

Annular Preventer BOP System Schematic

Ram Type Blowout Preventer

Ram type preventers  derive their name from the twin ram elements which make up their closing mechanism. Three types of ram preventers are available:
• Blind rams – which completely close off the wellbore when there is no pipe in the hole.
• Pipe rams – which seal off around a specific size of pipe thus sealing of the annulus. In 1980 variable rams were made available by manufacturers. These rams will close and seal on a range of drill pipe sizes.
• Shear rams which are the same as blind rams except that they can cut through drill pipe for emergency shut-in but should only be used as a last resort. A set of pipe rams may be installed below the shear rams to support the severed
drill string.

Blowout Preventer Ram Type

Ram type preventers derive their name from the twin ram elements which make up their closing mechanism. Three types of ram preventers are available:

• Blind rams – which completely close off the wellbore when there is no pipe in the hole.
• Pipe rams – which seal off around a specific size of pipe thus sealing of the annulus. In 1980 variable rams were made available by manufacturers. These rams will close and seal on a range of drill pipe sizes.
• Shear rams which are the same as blind rams except that they can cut through drill pipe for emergency shut-in but should only be used as a last resort.  A set of pipe rams may be installed below the shear rams to support the severed drill string.

Annular preventers seal off the annulus between the dril string and BOP stack. During normal well-bore operations, the BOP is kept fully open by holding the contractor piston down. This position permits passage of tools, casing and other items up to the full bore size of the BOP as well as providing maximum annulus flow of drilling fluids. The BOP is maintained in the open position by application of hydraulic pressure to the opening chamber, this ensures positive control of the piston during drilling and reduces wear caused by vibration. The contractor piston is raised by applying hydraulic pressure to the closing chamber. This raises the piston, which in
turn squeezes the steel reinforced packing unit inward to seal the annulus around the drill string. The closing pressure should be regulated with a separate pressure regulator valve for the annular BOP.
The packing unit is kept in compression throughout the sealing area thus assuring a tough, durable seal off against virtually any drill string shape, kelly, tool joint, pipe or tubing to full rated working pressure Application of opening chamber pressure returns the piston to the full down position allowing the packing unit to return to full open bore through the natural resiliency of the rubber. Read other drilling engineer

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