1.What is ahead?
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The casing head is an important connection between casing and wellhead equipment.Its lower end is connected to the surface casing pipe through threads, and its upper end is connected to the wellhead device or blowout preventer throughor clamps.
2. Characteristics of casing head
(1) The casing connection can be either threaded or slip connected, and hanging the casing is fast and convenient;
(2) The casing hanger adopts a rigid and rubber composite sealing structure, and a metal seal can also be used to enhance the sealing performance of the product;
(3) It is designed with a wear protection sleeve and a pressure test removal tool to facilitate the removal of the wear protection sleeve and pressure testing of the casing head;
(4) The upper flange is designed with pressure testing and secondary grease injection devices;
(5) Theconfiguration on the side of the casing head is designed according to user needs;
3.The function of casing head
The casing head is installed at the upper end of the surface casing string. It is used to hang all layers of casing other than the surface casing and to seal the wellhead device components of the casing annular space. Its main functions are as follows:
(1) Hang part or all of the weight of each layer of casing except the surface casing through a hanger;
(2) Connect wellhead devices such as blowout preventers;
(3) Form a pressure seal between the inner and outer casing strings;
(4) Provide an outlet to release the pressure that may accumulate between the two sets of pipe strings;
(5) In an emergency, fluid, such as well killing fluid or fire extinguishing agent, can be pumped into the well through the side hole of the casing head;
(6) Special operations: a. If the cementing quality is not good, cement can be replenished through multiple side holes. b. During acidification fracturing, pressure balancing fluid can be injected from the side holes.
4. Classification of casing heads
(1) According to the number of hanging casing layers
According to the number of suspended casing layers, it can be divided into: single-stage casing head, double-stage casing head, and three-stage casing head; single-stage casing head is generally used in low-pressure shallow formation production wells; double-stage casing head It is suitable for most areas with relatively clear formation pressure and is widely used; three-stage casing heads are generally used in high-pressure deep wells or exploration wells;
(2) According to the structural type of casing hanger
According to the structural type of the casing hanger, it can be divided into slip-type casing heads, mandrel-type (threaded) casing heads, and integral (welded) casing heads;
(3)According to the connection method between bodies
According to the connection method between bodies, it is divided into flange type casing head, clamp type casing head, and independent thread type (casing head in which the upper end of the hanging casing string and the lower end of the tubing head body are connected by threads);
(4) According to the structural type of the body
According to the structural type of the body, it is divided into single-piece casing head (one body is equipped with one hanger) and combined casing head (one body is equipped with multiple hangers).
5. Structure and sealing of casing head
The casing head consists of four-way, casing hanger, jackscrew assembly, flange-type parallel gate valve, connectors, pressure display mechanism, etc.
(1) Structure of casing head
The casing head is composed of four-way, casing hanger, jackscrew assembly, flange-type parallel gate valve, connectors, pressure display mechanism, etc.;
(2) Working principle of rubber seal
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The pipe head seal consists of the casing head body, BT-shaped rubber sealing ring, casing hanger, dovetail-shaped rubber sealing ring, jackscrew V-shaped sealing ring, and sealing gasket ring. The casing hanger seat is hung on the step of the casing head body. Due to the suspended weight of the casing, the contact between metal and metal creates a rigid passive seal, and the seal between the casing hanger and the casing is a thread seal.
The casing head spool has a BT seal that matches the outer diameter of the casing hanger (or casing outer diameter) and corresponding grease injection and pressure test holes. When used, high-pressure sealing grease must be injected from the grease injection valve before it can be used. BT seal works. If leakage occurs in the seal, sealing grease should be injected from the grease injection valve and pressure test valve respectively to make the seal continue to be effective. The grease injection pressure does not exceed the rated working pressure of the flange; if the casing is sealed, it does not exceed the rated allowable collapse pressure of the casing. The pressure test hole is used for the external sealing test of the casing hanger.
There is a jackscrew on the flange, which is used to lock the wear sleeve (protect the sealing surface), and lock the casing hanger after the casing hanger is installed. If leakage occurs at the top screw, the pressure cap can be tightened to make the seal effective. There are flanges on both sides of the four-way casing head. One end is connected to the flat valve (or blind flange), and the other end is connected to the flat valve, threaded flange, joint, stop valve and pressure gauge. The two casing layers can be observed through the pressure gauge. annular pressure between.
(3) Metal and rubber seal of casing head
The metal and rubber seal of the casing head consists of the casing head body, BT-shaped rubber sealing ring, upper metal sealing component, lower metal sealing component, casing hanger, dovetail-shaped rubber sealing ring, top wire V-shaped sealing ring, and sealing gasket ring The casing hanger seat is hung on the step of the casing head body. Due to the hanging weight of the casing, the metal-to-metal contact creates a rigid passive seal. The seal between the casing hanger and the casing is a thread seal; before installing the upper flange, the upper metal sealing ring is measured by measuring the position and size of the upper metal sealing ring in the upper flange hole, and then determining the thickness of the installation adjustment ring, so that The adjusting ring has a certain amount of interference in the upper flange hole. When the upper flange is connected to the casing head four-way, the adjusting ring is compressed through the casing head four-way to deform the upper metal sealing ring, thereby achieving the function of sealing the casing hanger.
The sealing principle of the lower metal sealing component of the casing hanger is to ensure the geometric dimensions of each part through the design of the metal sealing ring, casing head spool, and casing hanger, and use the 45° cone rotation on the top wire to The pressure ring of the lower metal sealing assembly is moved downward to deform the U-shaped ring of the metal sealing ring assembly, thereby achieving the function of a sealing casing hanger.
The casing head is an important connection between casing and wellhead. Its lower end is connected with the surface casing through the thread, and the upper end is connected with the wellhead (or BOP) through the flange or clamp.
a. Support the weight of each layer of casing other than the surface casing through the hanger;
b. Bear the weight of wellhead equipment;
c. Pressure seal can be formed between inner and outer casing strings;
d. Provide an outlet for the pressure that may accumulate between the two casing strings, or pump liquid (kill drilling fluid, water or efficient fire extinguishing agent, etc.) into the well in case of emergency;
e. Special operations in drilling and production technology can be carried out, such as:
(1) if the well is not fixed, it can be refilled with cement from the side port;
(2) when acid fracturing is carried out by taking stimulation measures, the pressure liquid can be injected from the side hole to balance the tubing pressure.
a. Casing connection can be either threaded connection or slip connection. Hanging casing is fast and convenient;
b. The casing hanger adopts the composite seal structure of rigidity and rubber, and can also adopt the metal seal, which enhances the sealing performance of the product;
c. Anti-wear sleeve and pressure test take-out tool are designed to facilitate the take-out of anti-wear sleeve and pressure test of casing head.
d. The upper flange is designed with a pressure test and secondary grease injection device.
e. The configuration of casing head side wing valve is designed according to the user's requirements;
a. According to the number of hanging casing layers:
Single-stage casing head (see Figure 1), double stage casing head (see Figure 2), and third stage casing head (see Figure 3);
b. According to the structure type of casing hanger:
Slip type casing head, screw-type casing head;
c. According to the connection mode between bodies:
Flange type casing head, clamp type casing head, and independent screw type (the casing head with thread connection between the upper end of hanging casing string and the lower end of tubing head body);
d. According to the structure of the body:
Single casing head (a hanger is installed in one body), combined casing head (multiple hangers are installed in one body);
1. The design and manufacture of the casing head shall be in accordance with the natural gas industry standard of the people's Republic of China SY / t- specification for wellhead equipment and Christmas tree and API Spec 6A 19th edition specification for wellhead equipment and Christmas tree equipment published by American Petroleum Institute;
2. During the inspection of casing head, the specification for wellhead equipment and Christmas tree (SY / t-) and the 19th edition of API Spec 6A (API Spec 6a) published by American Petroleum Institute shall be implemented;
The casing head is composed of four-way pipe, casing hanger, jacking screw assembly, flange type parallel gate valve, connector, pressure display mechanism, etc;
The casing head seal consists of casing head body, BT rubber seal ring, casing hanger, dovetail rubber seal ring, V-shaped top thread seal ring, and sealing gasket ring. The casing hanger seat is hung on the step of the casing head body. Due to the hanging weight of the casing, the contact between metal and metal produces a rigid passive seal. The seal between the casing hanger and the casing is a threaded seal.
The casing head four-way pipe has a BT seal matching with the casing hanger outer diameter (or casing outer diameter) and corresponding grease injection and pressure test holes. When using, high-pressure sealing grease must be injected from the grease injection valve to make the BT seal work. In case of leakage of the seal, the sealing grease shall be injected into the grease injection valve and the pressure test valve respectively to make the seal continue to take effect. The grease injection pressure shall not exceed the rated working pressure of the flange; if the casing is sealed, it shall not exceed the rated allowable collapse pressure of the casing. A pressure test hole is used for the external sealing test of the casing hanger.
The flange is equipped with jacking wire to lock the anti-abrasion sleeve (to protect the sealing surface). After the casing hanger is seated, it can lock the casing hanger. If there is leakage at the top wire, tighten the pressure cap to make the seal effective.
The flange at both sides of the casing head four-way, one end is connected with a flanged gate valve (or blind flange), the other end is connected with a flat valve, screw flange, joint, stop valve, and pressure gauge. Through the pressure gauge, the annulus pressure between two casing layers can be observed.
The metal and rubber seal of the casing head assembly consists of a casing head body, BT-shaped rubber seal ring, upper metal seal assembly, lower metal seal assembly, casing hanger, dovetail-shaped rubber seal ring, top wire V-shaped seal ring, and sealing gasket ring. The casing hanger seat is hung on the step of the casing head body. Due to the hanging weight of the casing, the contact between metal and metal will produce a rigid passive seal. The seal between the casing hanger and the casing is a threaded seal (see Figure 5); the upper metal seal ring is to measure the position size of the upper metal seal ring in the upper flange hole before installing the upper flange and then determine the thickness of the adjustment ring to make the adjustment ring emit a certain amount of interference in the upper flange hole. When the upper flange is connected with the casing head cross, the adjusting ring is compressed by the casing head cross to deform the upper metal sealing ring, so as to achieve the function of sealing the casing hanger.
The sealing principle of the lower metal seal assembly of the casing hanger is to ensure the geometric dimension of each part through the design of the metal seal ring, the casing head cross, and the casing hanger, and to make the pressure ring of the lower metal seal assembly go down and the U-ring of the metal seal ring assembly deforms by using the 45 ° conical surface rotation on
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