Creep Deformation in Shale at Submicron Scale

页岩是一种细粒沉积岩，由粘土、石英、长石、黄铁矿、碳酸盐和有机物质的混合物组成，形成高度异质的纳米复合材料。 作为一种密封岩石，页岩一直被用来在地下储存有毒的、长期存在的化学和放射性废物。 事实上，结晶岩和厚页岩序列长期以来一直被认为是主要的储存场所，因为页岩的抗断裂能力。 页岩的力学性质取决于其基本成分的性质，包括粘土颗粒和有机包裹体的性质，以及混合物的孔隙度。 在很大程度上由于其粘土和有机物含量，页岩表现出显著的蠕变变形，这可能会在区域范围内造成沉降问题，并改变其作为有毒废物密封的有效性，这些废物必须容纳数千年。 该奖项支持在纳米尺度上研究页岩蠕变变形行为的基础研究。 这种异质材料的机械性能的调查提供了深入了解蠕变的基本过程，其功能作为一个密封的关键尺度，以及允许解释蠕变现象在更大的尺度。纳米多孔材料的研究涉及材料科学、生物力学等多个学科。该项目支持一名女博士生，她将帮助扩大代表性不足的群体和本科生的参与。该项目结合实验室测试和数值模拟，研究页岩在纳米尺度上的蠕变特性。 实验包括纳米压痕测试，以确定页岩成分的基本机械性能，并使用全场透射X射线显微镜（TXM），在SLAC国家加速器实验室内的斯坦福大学同步辐射光源可用的稀缺资源与纳米级分辨率的孔隙结构的成像。 数值模拟包括一种新的配方的混合物理论的固体-固体混合物的软物质和硬物质，反映了现实的物理表示的页岩在亚微米尺度的非均质结构。 这两种物质之间的相互作用，具有截然不同的刚度和蠕变性能，可能揭示微裂纹形成和传播通过异质纳米复合材料的性质。 从建模的角度来看，混合物理论是第一次用于描绘在纳米尺度上的软物质和硬物质的固-固混合物。

Shale is a fine-grained sedimentary rock consisting of a mixture of clay, quartz, feldspar, pyrite, carbonate, and organic materials forming a highly heterogeneous nanocomposite. As a seal rock, shale has been used to contain toxic, long-lived chemical and radioactive waste products in the ground. In fact, crystalline rocks and thick shale sequences have long been considered as prime storage sites because of the shale's ability to resist fracture. The mechanical properties of shale depend on the properties of its basic constituents, including those of clay particles and organic inclusions, as well as the porosity of the mixture. Due in large part to its clay and organic content, shale exhibits significant creep deformation that can create subsidence issues on a regional scale, as well as alter its effectiveness as a seal for toxic waste products that must be contained for thousands of years. This award supports fundamental research to investigate the creep deformation behavior of shale at the nanometer scale. Investigation into the mechanical properties of this heterogeneous material provides insight into the fundamental processes governing creep at a scale critical for its function as a seal, as well as allows interpretation of the creep phenomena at larger scales. The research involves several disciplines including materials science, biomechanics, and other scientific disciplines concerned with the studies of nanoporous materials. It supports a female doctoral student who will help broaden the participation of underrepresented groups and undergraduate students.The project investigates the creep properties of shale at nanometer scale using a combination of laboratory testing and numerical modeling. Experiments include nanoindentation testing to determine basic mechanical properties of the shale constituents, and imaging of the pore structure with nanometer-scale resolution using full-field Transmission X-Ray Microscopy (TXM), a scarce resource available at the Stanford Synchrotron Radiation Lightsource within the SLAC National Accelerator Laboratory. Numerical modeling includes a novel formulation of mixture theory for solid-solid mixture of softer matter and harder matter, reflecting a realistic physical representation of the heterogeneous structure of shale at submicron scale. Interaction between these two matters, which possess starkly different stiffness and creep properties, could potentially shed light onto the nature by which micro-cracks form and propagate through a heterogeneous nanocomposite. From a modeling standpoint, mixture theory is used for the first time to delineate a solid-solid mixture of softer matter and harder matter at the nanometer scale.