Triaxial stress strength designing method for vertical well casing string

Abstract

The invention discloses a triaxial stress strength designing method for a vertical well casing string. The triaxial stress strength designing method for the vertical well casing string comprises the following steps of: determining the steel grade, the wall thickness and the setting lengths of a first-section casing; performing internal pressure strength check and tensile strength check on the top of the first-section casing; calculating the setting lengths Lon and Lan of the first-section casing; and performing internal strength and extrusion strength check on the first-section casing till the designed well depth is met. By simultaneously considering the influence of coactions of an axial force, an external extrusion force and an internal pressure on the strength of the casing, the magnitude of the triaxial stress is calculated, an equivalent stress is calculated and supposed to be equal to the yield strength of the casing, and the strength of the casing is designed, so that the design is more reasonable and the designed vertical well casing string is more durable.

Description

technical field [0001] The invention relates to a method for designing triaxial stress strength of casing strings in vertical wells. Background technique [0002] With the continuous deepening of exploration and development, the number of directional wells, horizontal wells and extended-reach wells is increasing, especially for the development of beach and offshore oil fields, due to the limitation of platform location and the needs of later management and production, all Directional wells and horizontal wells are used for development. In recent years, with the development of offshore oilfield exploration to shallow sea and deep sea, extended-reach wells have been increasingly adopted by oilfields due to their cost advantages, and more requirements have been put forward for the casing string strength design of extended-reach wells. high demands. Due to the large inclination angle, long open hole section, and deeper and deeper casing, the load acting on the casing of oil an...

AI Technical Summary

Problems solved by technology

However, with the development of drilling technology and the needs of exploration and development, the drilling depth is getting deeper, the geological conditions are becoming more and more complex, and the working conditions of oil wells are getting worse and worse. The uniaxial stress design and biaxial stress design can no longer meet the needs of drilling And the requirements of oil and gas well development often cause the early damage of oil and gas well casing

The problem with the biaxial stress method is that when using the biaxial stress method to design, although the interaction of external extrusion force, internal pressure and axial force is considered, the influence of radial stress is ignored

According to the experimental data in the relevant literature, the experimental data of the specimens with collapsed damage are far from the theoretical curve of the biaxial stress ellipse, and the degree of agreement between the two is not high. This experimental result shows that the biaxial stress design method has flaws

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