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，形成高度不均匀的纳米复合材料。作为一种封闭岩，页岩被用来在地下含有有毒的、寿命长的化学和放射性废物产品。事实上，结晶岩和厚页岩层序长期以来一直被认为是主要的储集地，因为页岩具有抵抗破裂的能力。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。页岩表现出显著的蠕变变形，这在很大程度上是由于其粘土和有机含量所致，这可能会在区域范围内造成下沉问题，并改变其作为有毒废物的密封材料的有效性，而有毒废物必须被封存数千年。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。对这种非均质材料的力学性能的研究有助于深入了解控制蠕变的基本过程，该过程对其作为密封件的功能至关重要，并允许在更大的尺度上解释蠕变现象。这项研究涉及多个学科，包括材料科学、生物力学和其他与纳米多孔材料研究有关的科学学科。该项目支持一名女性博士生，她将帮助扩大未被充分代表的群体和本科生的参与。该项目使用实验室测试和数值模拟相结合的方法，在纳米尺度上调查页岩的蠕变特性。实验包括纳米压痕测试，以确定页岩成分的基本机械性能，以及使用全场透射式X射线显微镜(TXM)以纳米级分辨率成像孔结构，这是SLAC国家加速器实验室内斯坦福大学同步辐射光源提供的稀缺资源。数值模拟包括软物质和硬物质的固固混合物理论的新公式，反映了页岩在亚微米尺度上的非均质结构的真实物理表示。这两种物质具有截然不同的硬度和蠕变特性，它们之间的相互作用可能会揭示微裂纹形成和传播通过非均质纳米复合材料的本质。从建模的角度，首次使用混合物理论在纳米尺度上描绘了较软物质和较硬物质的固体-固体混合物。

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.