Popularization of knowledge: basic function and function of casing head

Popularization of knowledge: basic function and function of casing head

The casing head is usually made of 35 or 42 chromium molybdenum alloy structural steel. A casing hanger is also arranged in the casing head to hang the casing string of corresponding specifications and seal the space gap of the ring. BOP stack shall be installed on it. After well completion, Christmas tree is installed on casing head.

Basic functions:

When drilling on land or offshore, in order to support and fix the casing string running into the well, BOP stack and other wellhead devices should be installed, and connected with the top of casing string through thread or flange, and located at the outer casing.

The production of casing head generally includes the following process flow:

1. Casting blank: casting material into workpiece blank.

2. Rough cutting, i.e. preliminary cutting of workpiece blank.

3. Finish turning, that is to use the lathe to process the rough machined workpiece to the designed accuracy.

4. Boring diameter: use boring machine to bore the designed inner diameter.

5. Drill, drill, drill out external connection bolts.

6. Heat treatment: the workpiece is quenched and tempered.

7. Inspection and test: after the machining process is completed, the geometric dimension, hardness, roughness and internal and external defects of casing head shall be inspected and NDT.

Function of casing head:

The casing head is installed at the upper end of the surface casing string, which is used to hang all casing layers except the surface casing and wellhead components, and seal the annular space of the casing. Its main functions are as follows:

1. Hang part or all weight of each layer of casing except surface casing with hanger;

2. Connect wellhead devices such as BOP;

3. A pressure seal is formed between the inner casing string and the outer casing string;

4. Provide an outlet to relieve the pressure that may accumulate between 20% casing strings;

5. In case of emergency, killing fluid or fire extinguishing agent can be pumped into the well through the side hole of casing head;

6. Special operation: A. if the cementing quality is not good, cement can be injected into the side hole; B. during acidizing and fracturing, the pressure balance fluid can be injected from the side hole.