The pressure of the
API 5CT oil casing in the oil well: to ensure that the casing enters the well continuously, without cracks or deformation, the casing is required to have a certain strength to resist the external force it receives. Therefore, it is necessary to analyze the stress on the casing of the inner well.
1) pull force
2) squeezing pressure
3) internal pressure
4) bending force
In short, the casing in the well is mainly subjected to the first three forces. The force of each component is different, the upper part bears the pulling force, the lower part bears the external pressure, and the middle bears little external force. When designing the casing string, the steel and wall thickness of the casing should be selected according to the above safety factor. For API standard casing, the general safety factor of tensile is 1.6-2.0, the impact safety factor is 1.00-1.50, generally 1.125, the internal pressure safety factor is 1.0-1.33, the safety factor of compressive strength is ideal value at cement injection point is 0.85. It should be emphasized that the safety factor of casing string strength design is carefully chosen according to the regional, stratigraphic, late production and gas production processes. He is an experience figure. Because of the different external forces on the middle and lower parts of the casing string, the upper and lower walls of the design of the casing string are often thick or more steel, and the middle is the opposite, so the number shell needs to be numbered. Go into this well. In most cases, bushing work in corrosive media. Therefore, in addition to requiring a certain degree of bonding strength, the casing also needs to have good sealing performance and corrosion resistance.
