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Casing head-Wellhead Equipment

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Casing head overview

Wellhead devices refer to Christmas trees.tubing heads,drive heads and related accessories, and are oil production equipment used for suspension, support, control, and adjustment.

As an important equipment for oil and gas production.its performance is related to the safe and efficient production of oil and gas wells.

Casing head

The casing head is an important connection between the casing and the wellhead.

Its lower end is connected with the surface casing through a thread.and the upper end is connected with a wellhead device,or a blowout preventer through a flange or a clamp.

Commonly used casing head

Features

The casing connection can be threaded connection or slip connection. Hanging casing is fast and convenient;

The casing hanger adopts a rigid and rubber compound sealing structure, and can also adopt a metal seal.which enhances the sealing performance of the product.

Designed with pressure test removal tool,and anti-wear sleeve  in order to facilitate the removal of the anti-wear sleeve and pressure test on the drive head.
The upper flange is designed with pressure test and secondary grease injection device
The flank valve configuration of the drive head is designed according to user requirements;

The role of casing head

The casing head is installed on the upper end of the surface casing string to suspend all layers of casing other than the surface casing and to seal the casing annular space. The main functions are as follows:

  • 1.Hang part or all of the weight of each layer of casing except for the surface casing through the 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 two percent of the casing strings;
  • 5.In an emergency,fluid, such as killing fluid or fire extinguishing agent.can be pumped into the well from the side hole of the drive head;
  • 6.Special operations: a. The cementing quality is not good, but the side holes can be refilled with cement. b. During acid fracturing, the pressure balance fluid can be injected from the side holes.

drive head structure of each layer


Supplement | Knowledge

For the sake of memory, the functions and uses of the drive head are summarized into four sentences:

Hanging the weight of each layer of casing

Support the blowout preventer above thedrive head;

Provide a seal between each layer of casing;

Provide channels for special operations;

Classification

1. According to the number of hanging casing layers

According to the number of suspended casing layers, it can be divided into: single-stage drive head, double-stage casing head, and three-stage drive head; among them, single-stage casing heads are generally used in production wells in low-pressure shallow formations; double-stage casing heads It is suitable for most areas where the formation pressure is relatively clear, and the amount of use is large; the three-stage casing head is generally used in high-pressure deep wells or exploration wells.

For instance:

Single stage 

Double-stage 

Three-stage 

2.According to the structure of casing hanger

According to the structure of the casing hanger, it can be divided into slip type drive head, mandrel type (thread type) drive head, and integral type (welded type) casing head;

Slip type 

Mandrel type

Integral (welded) 

3.According to the connection between the bodies

According to the connection mode between the bodies, it is divided into flange type drive head, clamp type drive head, and independent thread type.

(the upper end of the suspension casing string,and the lower end of the tubing head body are connected by threads);

4.According to the structure of the body

According to the structure of the main body, it is divided into single drive head.(one body is equipped with one hanger) and combined drive head.(one body is equipped with multiple hangers);

Model notation of casing head

Structure and sealing of casing head 

1.Structure of casing head

Above all,the drive head is composed of four-way, casing hanger, jack wire assembly, flange type parallel gate valve, connecting piece, pressure display mechanism, etc.

2.Working principle of rubber seal

 The drive head seal is composed of drive head body, BT-shaped rubber seal ring, casing hanger, dovetail rubber seal ring, top wire V-shaped seal ring, and gasket ring. The casing hanger seat is hung on the casing head body. On the step, due to the hanging weight of the casing, the metal-to-metal contact produces a rigid passive seal. The casing hanger and the casing are sealed by threaded seals.

 The casing head four-way 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 using it, high pressure sealing grease must be injected from the grease injection valve before it can be used.

The BT seal works. If the seal leaks, seal grease should be injected separately from the grease injection valve and the pressure test valve to make the seal continue to take effect. The pressure of the grease injection not exceed the rated working pressure of the flange ;it shall not exceed the rated allowable collapse pressure of the casing if it is sealed type .

The pressure test hole is used for the external sealing test of the casing hanger. There is a top wire on the flange, which is used to lock the anti-wear sleeve (to protect the sealing surface). After the casing hanger is seated, the casing hanger can be locked. If leakage occurs at the top wire, the compression cap can be tightened to make the seal effective.

Four-way flanges on both sides of the drive head, one end is connected to a flat valve (or blind flange), and the other end is connected to a flat valve, threaded flange, joint, stop valve and pressure gauge. The two casing layers can be observed by the pressure gauge. The annulus pressure between.

3. In conclusion,Metal and rubber seal of drive head

The metal and rubber seal of the casing head consists of the casing head body, BT-shaped rubber seal ring, upper metal seal assembly, lower metal seal assembly, casing hanger, dovetail rubber seal ring, top wire V-shaped seal ring, and 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 produces a rigid passive seal. The seal between the casing hanger and the casing is threaded seal (see the above figure);

the upper metal sealing ring is to measure.the position and size of the upper metal sealing ring in the upper flange hole before installing the upper flange, and then determine the installation and adjustment.

The thickness of the ring makes,the adjustment ring have a certain amount of interference in the upper flange hole.

I have in addition,when the upper flange is connected with the casing head four-way.the adjusting ring is compressed,by the drive head four-way to deform the upper metal sealing ring.then to  meet 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 seal ring.

the drive head cross and the casing hanger, and use the 45° cone rotation on the top wire to rotate.

We have the pressure ring of the lower metal seal assembly is moved down.and the U-shaped ring of the metal seal ring assembly is deformed.

so as to achieve the function of sealing the casing hanger.

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