RK Pipe & Supply offers new and used single, double, and annular blowout preventers from multiple manufacturers. Please see our online inventory and contact our sales department for information and quotes.
Annular-Type Blowout Preventer
An annular blowout preventer (BOP) is a drilling equipment component that is installed at the top of the BOP stack (see Figure 1A) and has the capability of closing (sealing off) on anything in the bore or completely shutting off (CSO) the open hole by applying closing pressure.
The sealing device of an annular blowout preventer is referred to as the “packing element”. It is basically a donut- shaped element made out of elastomeric material. To reinforce the elastomeric material, different shapes of metallic material are molded into the element.
This keeps the elastomeric material from extruding when operating system pressure or well bore pressure is applied to the bottom of the packing element. Since the packing element is exposed to different drilling environments (i.e., drilling fluid/mud and or temperature of the drilling fluid), it is important to make sure that the proper packing element is installed in the annular preventer for the anticipated environment of the drilling operation.
During normal drilling wellbore operations, the blowout preventer is kept fully open by leaving the piston in the open (down) position. This position permits passage of drilling equipment and tools, casing, and other items which are equal to the full bore size of the blowout preventer. The blowout preventer is maintained in the open position by relaxing all hydraulic control pressures to the closing chamber. Application of hydraulic pressure to the opening chamber ensures positive control of the piston.
Closing Pressure – Blowout Preventer Operation
In order for the annular blowout preventer to close on anything in the bore or to perform a complete shut-off, CSO, closing pressure must be applied. As the piston is moved to the closed position, the elastomer packer is squeezed inward to a sealing engagement with anything in the bore or on the open hole. Compression of the elastomer throughout the sealing area assures a strong, durable seal off against any shape, even with a previously used or damaged packer.
The piston is moved to the closed position by applying hydraulic pressure to the closing chamber. Guidelines for closing pressures are contained in the operational section for each manufacturer’s type of annular blowout preventer and in the Operator’s Manual. The correct closing pressure will ensure long life, whereas excessive or deficient closing pressures will reduce packer life. The pressure regulator valve of the hydraulic control unit should be adjusted to the manufacturer’s recommended closing pressure.
Subsea applications may require an adjustment of closing pressure due to effects of the hydrostatic head of the control fluid and of the drilling fluid column in the marine riser. The applicable Operator’s Manual will explain these requirements.
Stripping With An Annular Blowout Preventer (BOP)
Drill pipe can be rotated and tool joints stripped through a closed packer, while maintaining a full seal on the drill pipe. Longest packer life is obtained by adjusting the closing chamber pressure just low enough to maintain a seal on the drill pipe with a slight amount of drilling fluid leakage as the tool joint passes through the packer. The leakage indicates the lowest usable closing pressure for minimum packer wear and provides lubrication for the drill pipe motion through the packer.
A pressure regulator valve should be set to maintain the proper closing pressure. For stripping purposes, the regulator valve is usually too small and cannot respond fast enough for effective control, so a surge bottle is connected as closely as possible to the blowout preventer closing port (particularly for subsea installations). The surge bottle is precharged with nitrogen, and is installed in the BOP closing line in order to reduce the pressure surge which occurs each time a tool joint enters the closed packer during stripping. A properly installed surge bottle helps reduce packer wear when stripping. Check manufacturer’s recommendations for proper nitrogen precharge pressure for your particular operating requirements. In subsea operations, it is advisable to add an accumulator to the opening chamber line to prevent undesirable pressure variations.
Ram-Type Blowout Preventer
A ram-type blowout preventer is basically a large bore valve (see Figure 1B). The ram blowout preventer is designed to seal off the well bore when drill pipe, casing, or tubing is in the well. In a BOP stack, ram preventers are located between the annular blowout preventer and the wellhead (see Figure 2B). There are typically 3 or 4 ram preventers in a BOP stack. Flanged or hubbed side outlets are located on one or both sides of the ram BOPs. These outlets are sometimes used to attach the valved choke and kill lines to. The outlets enter the wellbore of the ram preventer immediately under the ram cavity.
Other than sealing off the well bore, rams can be used to hang-off the drill string. A pipe ram, closed around the drill pipe with the tool-joint resting on the top of the ram, can hold up to 600,000 lbs. of drill string.
Several different types of rams are installed in the ram type BOP body. The four main types of rams are Pipe Rams, Blind Rams, Shearing Blind Rams, and Variable Bore Rams. Following is a brief description of each type:
The rubber sealing element is flat and can seal the wellbore when there is nothing in it, i.e., “open hole”. (See Figure 3)
The sealing element is shaped to fit around a variety of tubulars, which include production tubing, drill pipe, drill collars, and casing that will seal off the wellbore around it. (See Figure 4)
Variable Bore Rams
The sealing element is much more complex and allows for sealing around a particular range of pipe sizes. (See Figure 5)
Shearing Blind Rams
The blade portion of the rams shears or cuts the drill pipe, and then a seal is obtained much like the blind ram. (See Figure 6)
NOTE – Also available are shear rams that are capable of shearing multiple tubing strings and large diameter tubulars while maintaining a reliable wellbore pressure seal.
Ram Locking Device
A ram locking device is necessary to be fitted to all ram blowout preventers. This device is used whenever it is necessary to remove hydraulic operating pressure from the “close” side of the ram operating system, but maintain the ram preventer in the close position. On BOP stacks that are used in a surface application, the ram locking device is a threaded rod, referred to as a “lock screw”. This lock screw reacts between the operating piston in the ram operating system, and the housing of the lock screw. The locking device on a ram preventer that is used in a subsea application must be designed to be remotely actuated by either the BOP hydraulic control unit, or by the actual movement of the operating piston in the ram operating system.