中文摘要：

针对井壁几何参数、力学性能参数和地层压力存在的随机性特点，对传统井壁稳定性系数评价方法的不足进行分析。根据可靠性理论，从力学角度建立井壁失稳风险评价方法。利用Monte-Carlo随机抽样法，计算井壁失稳的风险概率数值解，分析井壁围岩失稳风险概率分布规律，并与传统井壁稳定性系数进行对比，建立全井段井壁失稳风险评价方法。结果表明：井壁失稳风险评价方法和程序能够满足井壁失稳评价的需要；基于可靠性理论建立的井壁失稳风险评价方法．可对井壁的稳定性进行定量评价；井壁失稳风险概率评价指标．可为传统井壁稳定性系数的选取和不确定性条件下的井壁稳定性评价提供依据。

英文摘要：

For the stochastic property of borehole geometric parameters, mechanical properties and formation pressures, the deficiency of the traditional method of borehole stability coefficient was analyzed. According to the broad structural reliability theory, the risk assessment method of borehole instability was established from the perspective of mechanics. The distribution regularities of the borehole instability risk probabilities were simulated by Monte-Carlo random sampling method, and the instability risk probabilities distribution and the traditional borehole stability coefficient were discussed. The borehole instability risk assessment method of full well section was established. The results show that this method and program could meet the requirements of wellbore stability evaluation. The probabilistic method of borehole instability risk based on the reliability could be used to quantitatively evaluate borehole stability. The borehole instability risk probability could provide foundations for selection of borehole stability coefficient as well as evaluation of borehole stability under uncertainty conditions.