The casing is a steel pipe used to support the well wall of oil and gas wells, so as to ensure the normal operation of the whole oil well during the drilling process and after the completion of the well. According to different drilling depth and geological conditions, several layers of casing shall be used for each well. After casing running into the well, cement should be used for cementing. It is different from tubing and drill pipe, and can not be reused. It belongs to disposable consumption material.
*Casing pipe lines the borehole. It is liable to internal pressure by fluid purging, axial tension by its dead weight, and external pressure by surrounding rock formations. The casing is especially exposed to axial tension and internal pressure by the pumped oil or gas emulsion.
*Tubing is the pipe through which the oil or gas is transported from the wellbore. Tubing segments are generally around 30 ft [9 m] long with a threaded association on each end.