基于卸荷作用的深部围岩拉伸蠕变损伤演化机理及本构模型研究

Oil and gas well drilling and underground cavern excavating for the surrounding rock of deep high stress area is a long-term unloading process, while during this process the tensile stress is often appears. Due to the tensile strength of rock is only 1/6-1/32 of the compressive strength, therefore, using the traditional method of compression parameters has been unable to meet the needs of solving the deep surrounding rock rheological mechanics problems. In view of this, t In this project, the direct tensile creep test and the specimen fracture surface SEM test of the shale and sandstone that are in the deep oil and gas engineering and deep underground caverns marble will be take into account, while the deep hole creep damage simulation experiment and numerical simulation experiment were also carry out. On the basis of experimental research and combined with theory analysis, the tensile creep damage evolution mechanism of deep surrounding rock will be explored, the microscopic creep damage law of deep surrounding rock will be revealed, the function relationship between creep and damage will be discussed, finally, a tensile creep damage constitutive model of deep surrounding rock will be established that can widely used to describe in three stages of decay creep, steady creep and accelerated creep. Research on the surrounding rock deformation damage propagation prediction of oil and gas deep exploration holes and deep underground cavern has important theoretical significance and application prospects.

油气井的钻探与地下洞室的开挖对深部高地应力区的围岩是一个长期的卸荷过程，而卸荷过程中又往往伴随着拉应力的出现。由于岩石的抗拉强度仅为抗压强度的1/6-1/32，因而，传统沿用压缩参数的方法已不能满足解决深部围岩流变力学问题的需要。鉴于此，本项目将对深部油气工程中的页岩、砂岩以及深部地下洞室工程常见的大理岩等多种岩石展开室内直接拉伸蠕变试验、试样破裂面电镜扫描试验以及深部孔洞蠕变损伤相似模拟试验与数值模拟仿真试验。在试验研究的基础上，结合理论分析探索深部围岩拉伸蠕变损伤演化机理，揭示深部围岩拉伸蠕变细观破坏规律，探讨蠕变损伤函数关系，最终，建立一种深部岩体广泛适用的可描述衰减蠕变、稳态蠕变以及加速蠕变等三个阶段的拉伸蠕变损伤本构模型。研究成果对深部油气开采孔洞、深部地下洞室等围岩的变形与损伤扩展预测具有重要的理论意义与应用前景。

随着地下洞室工程建设的深度以及深部油气的开采深度的逐渐加深，面临的岩石流变力学问题尤为突出。而油气井的钻探与地下洞室的开挖对深部高地应力区的围岩是一个长期的卸荷过程，这一过程中又往往伴随着拉应力的出现。围绕开挖卸荷引起的拉应力条件下深部围岩蠕变损伤演化机理以及建立可以预测深部孔洞围岩在拉应力条件下变形与损伤扩展规律的拉伸蠕变损伤模型等拟解决的重要关键科学问题，采用现场调研、相似模拟实验、室内实验、理论分析和数值仿真相结合的研究方法，开展系统的研究。首先，结合页岩气井现场工程地质调查，开展了室内相似模拟实验获得了卸荷作用下井壁围岩变形破坏规律；其次，通过页岩、砂岩及大理岩等多种深部岩体的室内直接拉伸蠕变损伤实验获得了深部岩石的拉伸蠕变及损伤演化规律。在此基础上，构建了适合深井页岩的蠕变损伤本构模型，并将该模型与FLAC3D接合，实现了深井岩石的蠕变损伤数值模拟预测分析。研究成果为深井围岩缩颈等蠕变行为提供了新的研究方法与思路，可应用于深部地下工程的安全与长期稳定性评价，对深部油气开采孔洞、深部地下洞室等围岩的变形与损伤扩展预测具有重要的理论意义与应用前景。