断层扰动下地应力场三维有限元约束优化反演

3-D FEM inversion for the in-situ stress field around complex faults based on the theory of constrained optimization

在分析复杂断层构造扰动下的区块G的多点实测地应力分布特点的基础上,通过建立符合研究区地质特点的数值模型,采用基于有限元法及数学约束优化理论的有限元约束优化反演法对研究区的三维地应力场进行了模拟,得到了与实测值吻合良好的结果。通过对反演得到的地应力分布特征进行分析,探讨了复杂断层对区域地应力状态的影响。研究结果表明:断层附近的地应力分布主要受其邻近断层的扰动影响,且受扰乱程度与断层的几何尺寸以及离断层的距离等因素相关;由于断层的扰动作用,断层附近地应力分布十分复杂,尤其是断层端部尖灭区的地应力分布更是如此,因此,有限"点"的实测应力值不能全面反映断层发育区地应力场的全貌,三维数值模拟是区域地应力场定量分析与评价的不可缺少的手法。

According to the distribution characteristics of in-situ stresses measured in the fault-block G around complex faults,in-situ stress field is simulated and estimated by establishing numerical model suitable for geological structure of the block G and applying the COFEM method(constrained optimization finite element method) based on the FEM method and the theory of constrained optimization. Simulating results fit with the distribution characteristics of the measurements. In addition,the influence of complex faults on regional in-situ stresses is analyzed by comparing the in-situ measurements with numerical results. It is shown that the distribution of in-situ stresses around faults is mainly affected by its near faults,and depends mainly on the scale of the fault and the distance from the near fault. Because of the influence of the faults,the distribution of in-situ stresses around faults is complicated,especially the terminal portion of faults,the distribution of in-situ stresses field can not be generated by some discrete measuring points. Three-dimensional numerical simulation is very important for us to analyze and estimate the in-situ stresses field.