An Analysis of the Collapse Strength of Down-Hole Tubings Loaded by Axial Compressive Forces and Bending Moment

Due to collapses of tubings during well testing and completing in HPHT wells, it is required by Petrochina officially to calculate and analysis the collapse strength of down hole tubings with axial forces and corresponding bending moment being taken into considerations. Based on the 4th strength theorem, formulas were derived and method was present to analyze the collapse strength of down hole tubings loaded by compressive axial forces and bending moment to fulfill the official requirements, which could not be accomplished according to published standards and references. And, influences of axial tensile forces, compressive forces and bending loads on the collapse strengths of down hole tubings were studied. It is found that the collapse strength of down hole tubing loaded by compressive axial force is smaller with compressive axial force and buckling bending moment taking into considerations. The bigger the compressive axial forces, the smaller the collapse strengths.