Collaborative Research: Salt Rock Microstructure and Deformation

盐岩被用于安全储存石油、高压气体和核废料，因为它具有蠕变能力，并形成气体和流体流动的障碍。然而，地下储存设施附近的蠕变过程可能导致裂缝脱粘、打开、关闭和重新粘接，从而损害流动屏障的完整性和工程结构的稳定性。开裂和愈合的数学描述还不完全完善。该奖项将支持基础岩石物理和力学研究，将裂缝剥离、打开和重新粘合的变形与微观结构和力学变量联系起来，这些变量在地质空间和时间尺度上控制着盐岩的随时间变化的行为。盐的变形在实验室条件下发生迅速，使其成为研究其他晶体材料和多孔介质中的损伤和愈合的良好模拟物。项目发现有望推进定量关系，使工程项目行为的准确建模和预测成为可能。这项工作将促进对其他岩石的开裂和愈合的基本理解，这些岩石在同样的过程中变形，特别是在地震断层和诱发地震活动区附近。地球科学和工程研究人员团队将与其他项目合作，扩大妇女和其他代表性不足的群体在研究和工程领域的参与。大多数盐的连续损伤模型都是基于剪胀边界的概念，没有考虑到裂纹引起的弹性特性的各向异性。微观力学和均匀化原理成功地用于模拟盐岩弹塑性行为，但不能用于测试变形状态下微观结构的尺度不变性。本项目的目标是将盐的变形机制和流变行为与微观结构的密度和取向分布联系起来。代表性基本体积尺度上的变形机制将被分解为独立的过程（例如，开裂），每个过程都与不同的微观结构描述符（例如，晶粒长径比）相关。宏观热力学变量将与微观结构描述符正式相关，以测试变形制度中过渡点的空间和时间尺度不变性。具体的研究目标是：(1)确定盐微观结构的拓扑成分和子成分；(2)确定晶内和晶间裂纹的解粘、张开、闭合和重粘能量成本；(3)计算与晶粒和REV尺度变形机制转换相关的能量阈值；(4)测试相变过程中微观组织的时间和尺度依赖性；(5)设计岩盐微观结构系统，优化地下储存环境中的愈合性能。

Salt rock is used for secure storage of oil, high-pressure gas, and nuclear waste because of its ability to creep and form barriers to gas and fluid flow. However, creep processes near subsurface storage facilities can lead to crack debonding, opening, closure and rebonding that compromise the integrity of flow barriers and stability of engineered structures. Mathematical descriptions of cracking and healing are incompletely developed. This award will support fundamental rock physics and mechanics research to link deformation by crack debonding, opening and rebonding to microstructures and mechanical variables that govern the time-dependent behavior of salt rock over geological space and time scales. Deformation of salt occurs rapidly at laboratory conditions making it a good analog to study damage and healing in other crystalline materials and porous media. Project findings are expected to advance quantitative relations enabling accurate modeling and prediction of behaviors in engineering projects. The work will advance fundamental understanding of cracking and healing in other rocks that deform by the same processes, especially around earthquake faults and zones of induced seismicity. The team of geoscience and engineering researchers will collaborate with other programs to broaden the participation of women and other under-represented groups in research and engineering.Most continuum damage models for salt are based on the concept of dilatancy boundary, and do not account for crack-induced anisotropy of elastic properties. Micro-mechanics and homogenization principles were successfully employed to model salt rock elastoplastic behavior, but were not used to test scale invariance of microstructure to transitions in deformation regimes. The goal of this project is to link salt deformation regimes and rheological behaviors with the density and orientation distribution of microstructures. Deformation regimes at the scale of a Representative Elementary Volume will be decomposed into independent processes (e.g., cracking), each related to different microstructure descriptors (e.g., grain aspect ratio). Macroscopic thermodynamic variables will be formally related to the microstructure descriptors to test the space and time scale invariance of transition points in deformation regimes. Specific research objectives are to: (1) Identify topological components and subcomponents of salt microstructure; (2) Determine the energy cost of intra- and inter-granular crack debonding, opening, closure and rebonding; (3) Compute energy thresholds associated with transitions between deformation regimes at the grain and REV scales; (4) Test the time and scale dependence of microstructure organization during transitions; (5) Design rock salt microstructural systems that optimize healing properties in subsurface storage environments.