LIMIT STATE DESIGN OF OIL AND GAS WELL CASINGS

The design of oil and gas well casings is crucial for ensuring well integrity, operational safety, and economic efficiency. Traditionally, casing design relied on the working stress design (WSD) method, which applied uniform safety factors but often led to over-conservative or suboptimal solutions. This thesis advances the application of Limit State Design (LSD) for casing, a modern methodology that evaluates the probability of specific failure modes such as collapse, burst, and axial tension, rather than solely relying on fixed safety factors. By employing advanced analytical equations and finite element analysis, this study systematically investigates the effects of parameters like diameter-to-thickness ratio, ovality, eccentricity, material properties, and residual stress on casing performance. The results demonstrate that LSD enables engineers to select casing types and grades with a higher degree of confidence, optimizing both cost and safety by addressing real operational risks. Comparative analysis with experimental data confirms LSD's accuracy in predicting failure. Ultimately, LSD promotes a risk-based, tailored approach to well design, reducing material and operational costs while significantly improving safety margins, making it an effective alternative for modern oil and gas field applications.

Keywords:

Limit State Design , Oil and Gas Casings , Finite Element Analysis , Well Integrity , Structural Reliability