3D Experimental and Computational Studies of Crystallographic Effects on Creep and Fracture in Salt Rock

岩盐是一种被归类为蒸发物的沉积岩，是内陆海或任何封闭水体蒸发的结果，在自然界中可发现为层状或穹隆状地层。盐丘经常在其边缘圈闭石油、天然气和其他矿物。盐穴是在地下盐矿中形成的大型洞穴或洞穴，既可以是自然形成的，也可以是人为形成的。自20世纪70年代初以来，它们一直被用来储存不同类型的碳氢化合物，包括美国的战略石油储备。盐穴可能会成为二氧化碳、核废料和石油钻探作业废料的长期安全储存库。通过岩盐钻井带来了许多挑战，包括井筒的长期稳定性/完整性、侧向压力导致的套管坍塌以及钻井液-盐的相互作用。模拟任何材料，包括岩石等地质材料的断裂行为的准确性，取决于工程模型的保真度和裂纹体的几何表示。盐岩在蠕变变形过程中的各向异性响应与应力和温度有关，累积的蠕变应变影响断裂形核。当岩盐地层与热源和应力变化相互作用时，这种行为会带来许多挑战。对3D多晶岩中裂缝何时、何地和如何演化的更好和定量的理解具有许多重要的技术含义，对于模拟钻井、地热能量提取、碳封存、机械-岩石相互作用和爆炸侵彻具有潜在的好处。该项目(I)影响研究界并促进技术转让；(Ii)让少数族裔/女性本科生参与尖端工程研究；以及(Iii)通过高中生参与研究来吸引下一代科学家，激发他们对土木工程领域的兴趣，并有助于提高下一代土木工程教育者和专业人员的质量。现有现象学蠕变模型的一个关键局限性是，岩盐的各向异性响应没有表现在微观结构水平上。虽然在岩盐中确实存在捕捉各向异性的晶体塑性模型，但它们使用的是在较小的温度和应变率范围内有效的经验流速方程。目前，文献中对3D岩石试件的蠕变和断裂的晶体取向敏感模型明显缺乏，并与3D晶体结构的直接测量相结合。因此，这项研究将结合无损三维X射线衍射(3DXRD)、三维同步辐射显微计算机断层扫描(SMT)原位实验测量和三维晶体塑性建模，以增强当前对多晶岩石蠕变和裂纹形成和扩展机制的理解，这在许多方面都是前所未有的。PI最近证明了在岩石微结构中实验测量晶格应变的能力。这些增强的实验技术为我们提供了更丰富的数据集，用于校准考虑各向异性的微结构本构模型。通过采用基于位错机制的晶体塑性模型，我们计划阐明在岩盐晶体中产生观察到的蠕变和断裂响应的支配机制。

Rock salt, a sedimentary rock classified as an evaporate, forms as a result of evaporation of inland seas or any enclosed body of water, and can be found in nature as bedded or domal formations. Salt domes often trap oil, gas, and other minerals around their edges. Salt caverns are large cavities or chambers that form inside underground salt deposits either naturally by the effect of geological processes or are man-made. They have been used as storage for different types of hydrocarbons since early 1970s including the US strategic petroleum reserve. Salt caverns may potentially serve as a long-term and safe repository for carbon dioxide, nuclear waste, and the waste of oil drilling operations. Drilling through rock salt poses many challenges, including long-term wellbore stability/integrity, casing collapse due to lateral pressure, and drilling fluid-salt interaction. The accuracy with which the fracture behavior of any material can be simulated, including geological materials like rock, hinges upon the fidelity of both the engineering model and the geometrical representation of the cracked body. The anisotropic response of rock salt during creep deformations is stress and temperature dependent, and the accumulated creep strain influences fracture nucleation. This behavior creates many challenges when rock salt formations interact with sources of thermal and stress changes. An improved and quantitative understanding of when, where, and how cracks evolve within 3D polycrystalline rocks has many important technological implications with potential benefits for modeling drilling, geothermal-energy extraction, carbon sequestration, machine-rock interaction, and explosive penetration. This project (i) impacts the research community and promotes technology transfer; (ii) involves minority/female undergraduate students in conducting cutting-edge engineering research; and (iii) engages the next generation of scientists through the involvement of high school students in research, sparking their interest in the field of civil engineering and helping contribute to the quality of the next generation of civil engineering educators and professionals.A key limitation of existing phenomenological creep models is that rock salt's anisotropic response is not represented at the microstructural level. While crystal plasticity models for capturing anisotropy in rock salt do exist, they employ empirical flow rate equations which are valid for a narrow range of temperature and strain rate. Presently, there is an apparent lack of crystal-orientation-sensitive models in the literature for creep and fracture in 3D rock specimens coupled with direct measurements of 3D crystal structure. Thus, this research will combine nondestructive 3D x-ray diffraction (3DXRD), 3D synchrotron micro-computed tomography (SMT) in-situ experimental measurements, and 3D crystal-plasticity modeling to enhance current understanding of creep and crack formation and growth mechanisms in polycrystalline rock is unprecedented in many regards. The ability to experimentally measure lattice strains within the microstructure of rock has recently been demonstrated by the PI. These enhanced experimental techniques provide us with a richer dataset for calibrating the microstructural constitutive model accounting for anisotropy. By employing dislocation mechanism-based crystal plasticity models, we plan to elucidate the governing mechanisms operating in the halite crystals that yield the observed creep and fracture response.