The limit state equations of different casing failure modes of deep and ultra-deep wells were analyzed,and the corresponding theoretical formulas of failure probability were given. The casing continuous system was discretized into several basic elements,and system reliability calculation model of deep and ultra-deep wells was established. Taking an ultra-deep field (depth 7380m) as an example,the quantitative computation of reliability for casing system and its basic elements were calculated based on the model,and the reliability factors and main failure modes of the ultra-deep well casing were studied. The results showed that the main influencing factors of casing reliability of deep and ultra-deep wells were collapsing strength, external collapsing load and axial pressure;casing failure modes of deep and ultra-deep wells were instability and collapsing.%分析深井、超深井套管柱不同失效形式的极限状态方程,给出了相应的失效概率理论公式.在井深方向上将套管柱离散为多个基本单元,建立深井、超深井系统可靠度计算模型.以西部油田某超深井(井深7 380m)为例,利用系统可靠度模型对套管柱基本单元和整体可靠度进行定量计算,分析套管柱的可靠性影响因素和主要失效形式.计算结果表明,影响深井、超深井套管整体可靠度的主要因素为套管抗挤强度、外挤载荷和轴向压力；深井、超深井套管失效形式主要为失稳和挤毁.
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