Resistance of Cemented Concentric Casing Strings Under Nonuniform Loading

Abstract

Summary This paper discusses the case of two opposing unidirectional collapse loads uniformly distributed along the diameter of a single casing string and two cemented concentric casing strings. The stress distribution in the casing and cement and the deformation of the pipe are determined by adapting known solutions in the mathematical theory of elasticity to the problem of single- and dual-casing strings subjected to this type of loading. Results were obtained for the case of uniform hydrostatic radial collapse loads for the two casing sizes (9⅝ and 7 in.) and their cemented structures. The resistance of the single pipe to this type of nonuniform loading may drop to 11 % of its design resistance to uniform hydrostatic collapse pressure. The resistance of the cemented concentric strings under uniform and nonuniform loads is about the sum of the steel pipe resistances under the same conditions. The paper also includes the superposition of uniform and nonuniform collapse loads and the practical implications of these results. We conclude that nonuniform loading should be considered in casing design, especially opposite salt formations.