The choice of casing is very important. Generally, we follow the two characteristics of impact resistance and light weight. Of course, the price factor cannot be ignored. Many units nowadays often prefer thick-walled tubes when using casings. In fact, this is a misunderstanding. At present, the ordinary geological casing (such as D40) has a yield strength ≥ 390Mpa and a tensile strength ≥ 680Mpa; it is basically available in the case of a hole depth of about six meters, but once the hole is deep, the casing is easily broken and an accident occurs. In order to meet the deep hole heel requirements, the casing will greatly increase the durability after special treatment. The parameters can reach: yield strength ≥ 515Mpa, tensile strength ≥ 810Mpa; plus casing joints, which is beneficial to casing The rigidity, especially the cuff is to be chamfered where the casing joint and the casing are joined, so that the inner surface of the casing is smooth and the eccentric head can pass smoothly.