Specification of Casing Head

• Nominal size:9”, 11”, 13-3/8”, 21-1/4”

• Casing size:5”-16-3/4”

• Specifications: API 6A

• Types of casing heads:  Threaded bottom casing head,  Slip bottom casing head,  Welded bottom casing head

Casing head assembly consists of casing head, casing hanger, by pass valve and other accessories parts. It can meet the requirement of sealing of annular space between casing hanger and casing, and can meet the requirement of casing supporting as well;  it can resist to the corrosion of all kinds of medium.

Hanger for casing head and casing spool is designed with 45°shoulder and straight seat, with good load bearing capacity. Casing head can be designed into integral or split structure according to requirement. The connection type between casing head and surface casing can be weld type, thread type and slip type. The corresponding casing hanger structure types are slip type and thread (mandrel) type. Side outlet connection type can be thread type, Studded flange type and flange type. The bottom of casing head and casing spool has secondary sealing and sealing test connection point for casing.

 Casing head design and production 

The casing head is generally made of 35 or 42 chromium-molybdenum alloy structural steel. Casing hanger is also arranged in the casing head to hang the casing string of the corresponding specification and seal the annular space gap, and to install the blowout preventer group above. After well completion, the casing head is fitted with an oil Christmas tree.

Casing head production, generally has the following process:
1. Cast billet, cast material into semi-finished products
2. Coarse cutting, make initial machining of the semi-finished products.
3. Fine machining, use lathe to process the rough-cut piece to the designed precision.
4. Boring diameter, with boring machine to bore out the designed inside diameter.
5. Drilling hole, using drilling machine, drilling out the outer connecting bolt.
6. Heat treatment the workpiece.
7. Inspection the casing head with testing of geometric dimensions, hardness, roughness and internal and external defects.

Casing head function

Casing head is a special short joint located in the outer casing when drilling on land or sea, in order to support and fix the well casing string, installation bop stack and other wellhead device, and with thread or the flange plate connected with the top of the casing string. 

The function of the casing head is:
1. fix drill hole casing string, reliably seal the casing space of each layer; control the casing space pressure;
2. quickly and reliably connect the casing string;
3. prevent the drilling tool from wearing out the casing near the surface;
4. the possibility of vertical movement of casing column when the underground temperature is high;
5. through the casing annulus output and input interface of the casing head, the special operation can be filled in the special case.

The casing head can support larger casing weight than the so-called "simple casing head" (also known as wellhead flange) currently widely used in China, which makes the wellhead device more stable. It can withstand the pressure of the wellhead, so its work pressure can be consistent with the work pressure of the blowout preventer, so as to facilitate the serialization of wellhead device. It is produced in bulk by the factory and avoids the welding necessary for the "simple casing head", so it has better anti-sulfur performance and strength. Therefore, high pressure oil and gas fields, deep Wells and ultra-deep wells should be used to promote the use of this casing head to make the entire wellhead device more secure and reliable.