Surface casing: Install a casing head at the top and suspend and support subsequent layers of casing through the casing head; Isolate the shallow water layer and complex shallow bottom layer on the surface, so that the freshwater layer is not contaminated by drilling fluid

Intermediate casing (technical casing): Isolates layers with different formation pressures or complex formations that are prone to collapse and leakage.

Production casing: protects the production layer and provides a pathway for oil and gas to flow from the production layer to the ground.

Drilling liner: reduces the load on the drilling rig during casing and the load on the casing head after cementing, while saving a large amount of casing and cement, reducing cementing costs.