Usage:

 

Blowout preventers come in a variety of styles, sizes and pressure ratings. Several individual units serving various functions are combined to compose a blowout preventer stack. Multiple blowout preventers of the same type are frequently provided for redundancy, an important factor in the effectiveness of fail-safe devices.

 

The primary functions of a blowout preventer system are to:

Confine well fluid to the wellbore;

Provide means to add fluid to the wellbore;

Allow controlled volumes of fluid to be withdrawn from the wellbore.

 

Additionally, and in performing those primary functions, blowout preventer systems are used to:

Regulate and monitor wellbore pressure;

Center and hang off the drill string in the wellbore;

Shut in the well (e.g. seal the void, annulus, between drillpipe and casing);

Prevent the flow of formation fluid, influx, from the reservoir into the wellbore) ;

Seal the wellhead (close off the wellbore);

Sever the casing or drill pipe (in case of emergencies).

 

Types

 

BOPs come in two basic types, ram and annular. Both are often used together in drilling rig BOP stacks, typically with at least one annular BOP capping a stack of several ram BOPs. 

 

1.Ram blowout preventer

 

Introduction:

 

A ram-type BOP is similar in operation to a gate valve, but uses a pair of opposing steel plungers, rams. The rams extend toward the center of the wellbore to restrict flow or retract open in order to permit flow. The inner and top faces of the rams are fitted with packers (elastomeric seals) that press against each other, against the wellbore, and around tubing running through the wellbore. Outlets at the sides of the BOP housing (body) are used for connection to choke and kill lines or valves.
 

 

An annular-type blowout preventer can close around the drill string, casing or a non-cylindrical object, such as the kelly. Drill pipe including the larger-diameter tool joints (threaded connectors) can be "stripped" (i.e., moved vertically while pressure is contained below) through an annular preventer by careful control of the hydraulic closing pressure. Annular blowout preventers are also effective at maintaining a seal around the drillpipe even as it rotates during drilling. Regulations typically require that an annular preventer be able to completely close a wellbore, but annular preventers are generally not as effective as ram preventers in maintaining a seal on an open hole. Annular BOPs are typically located at the top of a BOP stack, with one or two annular preventers positioned above a series of several ram preventers.

 

Function:

 

An annular blowout preventer uses the principle of a wedge to shut in the wellbore. It has a donut-like rubber seal, known as anelastomeric packing unit, reinforced with steel ribs. The packing unit is situated in the BOP housing between the head and hydraulic piston. When the piston is actuated, its upward thrust forces the packing unit to constrict, like a sphincter, sealing the annulus or openhole. Annular preventers have only two moving parts, piston and packing unit, making them simple and easy to maintain relative to ram preventers.

 

Category

 

Annular BOP using the spherical packing element


Annular BOP using the conical packing element


Annular BOP using the Combined packing element