1. Lower casing
Different from the drill pipe, the casing is a one-time running pipe without any thickening and the length is not strictly specified. In order to ensure the quality of cementing and the smooth running of the casing, the structural design of the casing string should be done. The strength of the casing is designed according to the application, the predicted pressure of the formation and the running depth of the casing, and the used wall thickness, steel grade and thread type of the casing are determined.

2. Cement
Cementing is a key process after the casing is put into the well. Its function is to seal the annular space between the casing and the well wall to seal off the oil and gas water layer, so that the casing becomes the channel for oil and gas to the well.
3. Wellhead installation and casing pressure testing
After the casing is cemented, the wellhead is installed while the cement sets. The top of the surface casing is to be fitted with the casing of the casing. The top of each layer of casing is hung in the casing head, and the casing head is mainly used to support the weight of the technical casing and the oil layer casing, which is particularly important when the cementing cement does not return to the surface. The casing head is also used to seal the annular space between the casings to prevent pressure from channeling each other. The casing head is also a transitional connection between the blowout preventer and the tubing head. There are also two side openings on the casing head used on land, which can supplement cement and monitor well conditions. Inject balancing fluid, etc.
4. Check the cementing quality
After the casing head is installed and the blowout preventer and the blowout preventer are connected, the pressure resistance inspection of the casing head seal and the sealing pressure test of the connection with the blowout preventer should be performed. After the cement plug in the casing is probed, the pressure test of the casing string shall be carried out, and the formation fracturing test shall be carried out after drilling through the casing shoe for 2-3 meters (technical casing). The quality inspection of the cement sheath should be done in the production well, and the cementation between the cement sheath and the casing and the well wall should be detected by sound waves. After all the indicators of cementing quality are qualified, the next operation procedure can be entered.