The stress on the API 5CT oil casing in the oil well: to ensure that the casing running into the well is continuous, not cracked or deformed, the casing is required to have a certain strength, enough to resist the external force it receives. Therefore, it is necessary to analyze the stress on the inner well casing.
1) Pulling force
2) Extrusion force
3) Internal pressure
4) Bending force
In conclusion, the casing in the well mainly bears the first three forces. The stress conditions of the various parts are different, the upper part receives the pulling force, the lower part has the outer pressing force, and the middle part receives less external force. When designing the casing string, the steel grade and wall thickness of the casing are selected based on the above consideration of the safety factor. For the API standard casing, the general safety factor for tensile is 1.6-2.0, the safety factor for impact resistance is 1.00-1.50, generally 1.125, the safety factor for internal pressure is 1.0-1.33, and the safety factor for the compression resistance at the cement injection site is The desirable value is 0.85. It should be emphasized that the safety factor in the design of casing string strength is carefully selected according to the region, stratum and the later oil extraction and gas production process. He is an empirical figure. Due to the different external forces applied to the upper, middle and lower parts of the casing string, the designed casing string is often thicker or more steel grades in the upper and lower walls, and opposite in the middle, so it is necessary to number the casing. Into this well. In most cases, the casing is working in corrosive media. Therefore, in addition to requiring a certain degree of joint strength, the casing is required to have good sealing performance and to be resistant to corrosion.
Post time: Sep-15-2023