OCTG casing is a steel pipe supporting oil and gas well wall, which ensures the normal operation of the entire well after the drilling process carried out. Different from tubing and drill pipe, casing can not be repeated use and belongs to a one-time consumption of materials. Therefore, the consumption of the casing pipe accounted for more than 70% of all. According to the situation of use, casing can be divided into: tube, surface casing, technical casing and oil layer casing.
In the first drilling, it is used to drill the soft ground until the bedrock layer. In order to seal this part of the formation without collapse, general use surface casing to seal.The depth of the surface casing depends on the depth of the soft ground, generally 80~1500 m. Its external pressure and internal pressure is not large, generally using K55 steel grade or N80 steel grade.
Because some wells are deep and complex and the depth of the well is several kilometers, this kind of deep well needs to use the technical casing. Its mechanical properties and sealing performance requirements are very high, the steel grade is also higher. In addition to K55, most of it use N80 and P110 steel grade and some deep wells also use Q125.
Oil layer casing
When drilling to the oil layer, the oil layer casing is used to seal hydrocarbon reservoir and the internal of it is tubing. The oil layer casing is the deepest in the different casing and the mechanical properties and sealing performance requirements of it are the highest.