A New High Collapse OCTG Collapse Strength Model Based on Twin Shear Unified Strength Theory

Abstract

Drilling through and completing wells through deep and acid environment regions are technically challenging and costly. Based on twin shear unified strength theory (TSUST), a new high collapse (HC) oil country tubular goods (OCTG) collapse strength model, involving the manufacturing imperfections and significant anisotropy of the material, was developed in this paper. Comparisons of numerical calculations with fullscale test collapse data show that the new HC OCTG collapse strength model gets higher calculation accuracy for predicating HC OCTG collapse strength than both American Petroleum Institute (API) Bulletin 5C3 and ISO/TR 10400. Thus, the new HC OCTG collapse strength model will provide a more scientific method and exciting possibility for deep and acid environment wells design and construction.