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Introduction to blowout preventer
Well control equipment is the important equipment used to control the well blowout in the process of drilling and prevent the uncontrolled blowout accidents. It can control the wellhead pressure, achieve near balanced or underbalanced drilling, improve the drilling speed and quality, and discover and protect the oil and gas reservoir to the max. Blowout preventer is the core part of well control equipment.
1. Introduction to blowout
Hydrocarbon accumulations are becoming more and more difficult to find, and oilmen are drilling deeper and deeper in their search for them. At some depth, pressures are extremely high, so there is always the risk of a blowout. A well that blows out of control is known as "gusher" or a "wild well".
The Lucas gusher at Spindle top, near Beaumont, Texas, which blew on January 10th 1901, was probably the most highly publicized of all oil – well blowouts.
Oil – well blowouts are wasteful, not only of time and money spent for control, but of pressure in the formation, which is needed to move the oil from the underground reservoir and raise it to the surface. Although blowouts have caused losses of life and property, experienced crews can minimize the danger by taking the necessary precautions, recognizing the signs of an imminent flow, not panicking when a well kicks, and using their equipment properly.
Most of the signs of a developing blowout were observable on the Lucas well: (1) Shows of oil and gas in the mud; (2) Drilling break, i.e., faster drilling; (3) Flow of mud from the well; (4) Pit gain; and (5) Lightened drill-string weight.
A blowout is an uncontrolled flow of fluid or gas from a wellbore or into lower-pressure subsurface zones.
2. Introduction to well control
The drilling fluid that courses through the system also provides the first line of defense against blowouts. A blowout can be an impressive sight. Gas, oil, or salt water spews into the air with a tremendous roar. If gas is present, the whole thing will probably be on fire, and the rig will lie as a melted, twisted mass of junk, Human lives are threatened; pollution may occur; precious oil or gas is wasted; and a rig worth many thousands or even millions of dollars may be a total loss.
On land rigs and on offshore rigs, such as platforms and jackups that are not floaters, BOPs are attached to the top of the well beneath the rig floor. The preventers are nothing more than large, high-pressure valves capable of being remotely controlled. When closed, they form a pressure-tight seal at the top of the well and prevent the escape of fluids. On floating offshore rigs, such as semisubmersibles and drill ships, the blowout preventers are attached to the well on the seafloor.
Two basic types of blowout preventers are annular are annular and ram. The annular blowout preventer is usually mounted at the very top of the stack of blowout preventers. It is called an annular because it seals off the annulus between the drill pipe or Kelly and the side of the hole. An annular BOP can also seal off an open hole – a hole that has no pipe in it. Below the annular preventer in blowout preventer stack are typicallyt mounted two, three, or even four ram-type blowout preventers. Ram preventers get their name from the fact that the devices that seal off the well are large, rubber-faced blocks of steel that are rammed together, much like a couple of fighting rams butting heads. Of the ram-type preventers there are blind rams, which seal off open hole, and pipe rams, which seal off the hole when drill pipe is in use. Usually, only the annular preventer will be closed when the well kicks, but should it fail, or should it be necessary to use special techniques, the ram-type preventers are used as a backup.
Of course, closing in the well with one or more of the blowout preventer is installed as part of the system. A choke is simply a valve whose opening is capable of being restricted or pinched in. It can be fully closed or fully open, and it may be infinitely variable in size between open and closed. In order to circulate the kick out of the well and pump heavy mud in, the choke is fully opened, the mud pump started, and, as the kick starts moving up the hole, the choke opening reduced in size by an amount that holds just enough back-pressure to allow the mud and kick out but prevents further entry of formation fluid. Once the kick is out and the heavier mud is in, a few checks are made, and normal drilling operations can resume. s is only the first step that must be taken. In order to resume drilling, the kick must be circulated out and mud of the proper weight circulated in. Therefore, a series of valves called the choke manifold.
3. Introduction to blowout preventers
Blowout preventers, in conjunction with other equipment and techniques, are used to close the well in and allow the crew to control a kick before it becomes a blowout. The two basic types of blowout preventers on a drilling rig are annular preventers and ram preventers. An annular preventer has a rubber sealing element that, when activated, closes tightly around the kelly, drill pipe, or drill collars or, if no part of the drill stem is in the hole, closes on the open hole. Ram preventers consist of large steel valves (the rams) that have sealing elements. One type of ram preventer is called a pipe ram because it closes on the drill pipe and is not able to affect a seal on open hole. Bind ram preventers are used to close on open hole.
Usually several blowout preventers are installed on top of the well in a stack with the annular preventer at the top of the stack and the pipe rams and blind rams below. Several preventers are installed together in this way so that an impending blowout, or kick, can be controlled even if one or more of the preventers fails.
Blowout preventers are opened and closed by hydraulic fluid, which is stored under pressure in a device called an accumulator. Several bottle or ball-shaped containers are located on the operating unit, and hydraulic fluid is stored in these containers. Rugged high-pressure lines carry the hydraulic fluid from the accumulator to the BOP stack and when control valves are actuated by the driller the fluid operates the preventers. Because the preventers must close quickly when needed, the hydraulic fluid is put under 1500 to 3000 psi of pressure by the nitrogen gas in the bottles or balls.
1) Differences between RAM blowout preventer (BOP) and annular blowout preventer (BOP)
A ram blowout preventer utilizes two horizontally opposed hydraulic rams that either close around the drill string, shear through the drill string and then seal, or close off a wellbore when no drill pipe or tubing is in it. An annular blowout preventer, also known as a spherical blowout preventer, utilizes a hemispherical piece of rubber reinforced with steel. Unlike a ram blowout preventer which closes with a sharp horizontal motion, the annular blowout preventer closes around the drill string in a smooth simultaneous upward and inward motion. The annular design also allows a much lower operating pressure, reducing the number of hydraulic accumulators necessary and thereby reducing cost and complexity of the operation.
2) Inner blowout preventer (BOP)
Inner blowout preventer is a flexible blowout control tool at wellhead. When well kick or blowout happening, an inner blowout preventer is connect to the top of drill string to control the well kick and blowout.
Control equipment of blowout preventer (BOP)
The QY series products can control two to eight heads and can respectively or simultaneously meet the requirements of controlling the open/close operation of annual blowout preventer, single or double ram blowout preventer and hydraulic valve. The hydraulic control pressure reaches 21MPa to make the sealing of the hydraulic pressure blowout preventer more reliable.
Blowout preventer ram
Currently there are two successful variable bore blowout preventer rams: Φ114-140mm ram supporting FZ35-25 BOP and Φ89-127mm ram supporting FZ35-70 blowout preventer.
Cross, rising nipple and adapter flange
Nowadays, there are such three connected forms with flanged, studded and hubbed of the end and exit of domestic blowout preventers for customers to choose. The pad ring slot has been welded with the stainless steel cover according to API Spec 6A Specification, which has extended the life cycle of the body and decreased the maintenance costs. Cross, rising nipple and adapter flange can be designed according to customers’ needs into all kinds of models and sizes to meet the requirement of the field operation to the max.
Materials for blowout preventer (BOP)
The important bearing-pressure components such as the blowout preventer shell are made of 25CrNiMo alloy steel in line with U.S. ANSI Standard replacing ZJ18CrMnSiMoV and 20CrMoV alloy steel. Meanwhile the forging process, the casting process and heat treatment have been improved. What’s more, the comprehensive performances of the materials, such as hardness and toughness, have been enhanced to reduce greatly the shell breakage fracture. To avoid the failure of the bolt breakage in their early serving time, the blowout preventer side-door bolts use 42CrMo material with the improved heat treatment technology.
In respect of rubber sealing materials, the hydrolysis resistant H-PU developed by China experts has overcome the shortcoming of the common H-PU with poor hydrolysis resistance and has good performances of anti-H2S and low temperature resistance, suitable for the working conditions of packing elements. The hydrolysis resistant H-PU has showed good effect after various tests.
Sealing structure of blowout preventer (BOP)
The new technologies such as stainless steel welding and the abrasion-resistant and corrosion-resistant alloy plating are used to protect the blowout preventer’s important sealing surfaces, which can prolong the working life of the equipment; the structure has been improved to eliminate the acting force of the well pressure on elastic baffle ring; The material of elastic baffle ring has been changed form 65Mn into special anti-sulfur stainless steel to enhance the reliability of blowout preventers.
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