Study On Safety Evaluation For Single-Leg Jacket Platform

With the rapid development of economy in China, the need of energy source is increasing continually. The exploitation of offshore oil field is the key to make up with the lack of continental oil field. The platform is becoming more and more important as the base of oil exploitation. The proved reserve of marginal oil field exceeds 1.3 billion tons in offshore. For both our country or the exploiting department and designer, it is crucial to invent and manufacture a kind of light, safe and reliable platform to exploit the marginal oil field. This paper studied the safety on the CB271 single-leg jacket platform in ShengLi Oil Field.Firstly, three kinds of FEM models considered fixed pile, equivalent pile, and spring-damper pile respectively was founded by means of the software ANSYS. The numerical results from the above FEM models was compared with the one of in-site test. The model of spring-damper pile is better than the others and is confirmed the numerical simulating model.Secondly, static and dynamic analysis on the single-leg jacket platform was employed. Three environmental cases such as normal wave, extreme wave and extreme ice were performed in static analysis. Meanwhile, earthquake response spectrum analysis was carried out in dynamic cases. Based on the above results, the checks of strength, stability and shear were executed. The results show that the jacket platform satisfies the request of strength and stability.Thirdly, the paper analyses the reliability of the single-leg jacket platform. Response analysis on the jacket platform based on finite element method was performed under environmental loading including wave and ice. Both analysis on member reliability and system reliability were accomplished on the base of the above FEM results. Monte-Carlo method considered four failure modes was used on member reliability analysis, and the range of failure probability for each member was obtained. Then, the range of system reliability considered the platform as series mode was achieved. Meanwhile, Sensitivity analysis is presented to study the influential factors on member reliability.Fourthly, the paper analyses the fatigue and fracture property of the single-leg jacket platform. Using elastic and plastic hypothesis and Miner cumulation fatigue synthesis rule, establishing the cycle time and cycle scale to analyze fatigue property. The result shows thatthe jacket platform satisfies the need of fixed number using years. In fracture analysis, using the calculation result from ANSYS software and fracture theory formula to gain the stress intensity factor K, and based on fracture criterion confirm that the jacket platform satisfy the request of fracture intensity.Finally, the paper draws the conclusion through all above calculation and brings forward the rational advice about the single-leg jacket platform.