A calculation method for ultimate and allowable loads in high-pressure thick-walled worn casing

• Published in: Ocean engineering 2024-12, Vol.313, p.119448, Article 119448
• Main Authors: Shi, Junlin, Zhang, Qiang, Lian, Zhanghua, Ding, Liangliang, Wan, Zhiyong
• Format: Article
• Language: English
• Subjects: Allowable load; Elastic-plastic finite element analysis; High pressure thick walled casing; Limit load; Wear of casing
• ISSN: 0029-8018
• DOI: 10.1016/j.oceaneng.2024.119448

Casing wear has become a critical issue in oil and gas drilling, significantly reducing casing burst strength. As exploration and development progress, the number of high-pressure, ultra-deep wells continues to rise, requiring high-strength, thick-walled casings capable of withstanding ultra-high internal pressures. However, research on the strength characteristics of worn high-strength, thick-walled casings under such conditions remains limited. This study fills that gap by quantitatively evaluating worn casings to determine the maximum allowable internal pressure, particularly for high-pressure, thick-walled casings. A systematic analysis of existing methods for calculating the ultimate load of casings is conducted, and a suitable approach for high-grade steel casings is proposed. A parametric finite element model (FEM) of worn casings was developed to assess the impact of various dimensionless structural parameters, including the thickness ratio (Do/t), wear percentage (h/t), wear circle ratio (2ri/Do), and nominal yield strength (Rp0.2), on the ultimate load. The results demonstrate that both wear depth and casing dimensions significantly affect the ultimate load. A new formula is proposed for calculating the ultimate and allowable loads of worn casings based on the results of a finite element analysis. This formula is applicable to high-strength casings of varying wall thicknesses, particularly under ultra-high pressure. •Proposed a method for determining the ultimate load of high-grade steel casings.•Established a calculation formula for the allowable load of high-strength, thick-walled worn casings.•Compared and verified different methods for determining ultimate loads.•Conducted finite element analysis to study the influence of casing wear parameters.