Collapse Strength Study for the Solid Expandable Tubular

The paper summarized an experimental and theoretical study of the collapse resistant ability of solid expandable tubular （SET）after expansion, and the formula used to calculate the collapse strength of casing was modified to make it adaptable to the expandable tubular. One key limiting factor of the expandable tubular in its application in the open hole well to replace the casing is its postexpanded mechanical properties. The collapse strength of the expandable tubular after expansion was significantly compromised as the result of the comprehensive influence by the change of factors like the ovality, eccentricity and residual stress. In view of these problems, firstly full-scale expansion experiments were performed to examine all the impact of those factors; secondly the formula was modified based on the experimental data; thirdly the collapse experiments were carried out to test the strength of post-expanded tubulars as well as the accuracy of the modified formula. The results demonstrated that after large-scale plastic deformation, the dimension of the tubular changed dramatically as represented by the increase of eccentricity and ovality, the residual stress also appeared on both inside and outside surface of the tubular, the starting point of the collapse occurred at the position with the least wall thickness. The calculation results which reflected the average collapse strength of the tubular were larger than the actual experimental outcome but the error was kept well within 15%. We expect the research will contribute to the better understanding of the collapse resistant ability of post-expanded tubular and form the necessary technical basis for it future broad use.