基于统一强度理论的泥页岩蠕变损伤强度解

The creep strength solution of mud shale based on the twin shear unified strength theory

针对目前泥页岩井壁蠕变计算未考虑中间主应力的问题,依据双剪统一强度理论,引入中间主应力参数b,通过理论分析和实践验证,推导了三轴试验条件下泥页岩蠕变损伤强度准则表达式,分析了b值、时间、井壁深度等因素变化对井壁蠕变的影响。结果表明:中间主应力对浅层井壁蠕变的影响较大,考虑中间主应力的作用将会进一步加剧泥页岩的蠕变;中间主应力的作用会使短时间泥页岩蠕变值有较大上升,因此应结合工程实际合理选择相应的中间主应力参数。依据本文所建立的泥页岩蠕变损伤强度准则可以考察中间主应力对泥页岩蠕变变形的影响,同时进一步预测不同时间段泥页岩的变形情况,为现场井壁稳定的判别提供理论支撑。

As the theoretical values of mud shale creep are not considering the intermediate principal stress effect,with the twin shear unified strength theory and the mechanic model of wellbore rock,the creep strength solution of mud shale is analyzed and derived under triaxial test conditions. Furthermore,the factors such as b value,time,depth are analyzed in order to evaluate their effects on wellbore creep. The results show that the intermediate principal stress has greater impact on shallow wellbore creep. And considering the intermediate principal stress effect will aggravate the creep of the mud shale. The effect of the intermediate principal stress will increase the creep value in a short period of time. So it is important to select the proper b value according to theactual project. The deduced creep damage strength criterion of mud shale based on the twin shear unified strength theory in this article can offer theoretical support for site wellbore stability discrimination and predict the deformation of mud shale in different time periods by changing the value of b.