Effect Of Variable Drill Pipe Sizes On Casing Wear Collapse Strength

Casing wear, on the process of drilling complex structure well, has resulted in the casing collapse strength being weaker, which could be one of the important causes of casing damage accidents. For the complex structure wells with variable drill pipe size, a bigger error would occur if the casing wear is calculated by the single size crescent wear model.In this paper, based on the hypothesis of the single size crescent wear and the size of the drill pipe joints being involved in wear, we have established two geometric models, named compound sharp wear and compound blunt wear and deduced the casing collapse strength formula considering the compound wear. Meanwhile, how the compound wear rained influence on casing collapse strength was also analyzed with two methods-analytical and finite element analysis.At the same wear depth, for the collapse strength, there are not many differences between the compound crescent wear casing and the single crescent wear casing with minimum wear radius and the maximum error, less than 5%, would decrease as the wear depth increased. That was why we regarded the latter as an approximation of the former to calculate the collapse strength of compound wear casing in our study, which will provide references for the deformation mechanism and strength analysis of casing section in complex cases.