Casing failure mechanism and strength design considerations for deep and ultra-deep wells

During deep and ultra-deep well developing, casings failure has brought great economic loss and safety hazards. Cas- ing failure forms and mechanism are analyzed, which mainly includes axial force causing thread off and destabilization, non-uniform loading resulting to collapse, shear deformation, thread losing effectiveness, internal wall wear and corruption. When complete a deep and ultra-deep well casing program, especially a gas well, strength design, thread sealing design and anticorrosion design are needed to introduce. Meanwhile, many factors including external loadings, casing strength models selection, plastic rock creep stress, intermediate casing wear, temperature effect, thread air tight ability are necessarily considered. The coeficient of safety design method is suggested to combined failure probability method in deep and ultra-deep well casing strength design and assessment. The domestic casing criteria and standards are proposed to improve.