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

岩盐是一种沉积岩，被归类为蒸发岩，是内海或任何封闭水体蒸发的结果，可以在自然界中以层状或穹窿状地层的形式发现。 盐丘通常在其边缘捕获石油，天然气和其他矿物。 盐穴是在地下盐矿床内部形成的大型洞穴或室，无论是自然的地质作用还是人为的。 自20世纪70年代初以来，它们一直被用作不同类型碳氢化合物的储存，包括美国战略石油储备。 盐穴有可能成为二氧化碳、核废料和石油钻井作业废料的长期安全储存库。 钻穿岩盐带来了许多挑战，包括长期井筒稳定性/完整性、由于侧向压力引起的套管坍塌以及钻井液-盐相互作用。 任何材料（包括岩石等地质材料）断裂行为的模拟精度取决于工程模型和裂纹体几何表示的保真度。 盐岩在蠕变过程中的各向异性响应是应力和温度相关的，累积蠕变应变影响裂纹形核。 当岩盐地层与热和应力变化源相互作用时，这种行为产生了许多挑战。 一个改进的和定量的了解，何时，何地，以及如何在三维多晶岩石中的裂缝演变有许多重要的技术意义与建模钻井，地热能提取，碳封存，机器-岩石相互作用，爆炸渗透的潜在利益。 该项目（一）影响研究界并促进技术转让;（二）使少数民族/女本科生参与进行尖端工程研究;以及（iii）通过高中生参与研究，吸引下一代科学家，激发他们对土木工程领域的兴趣，并帮助提高下一代土木工程教育工作者的素质，现有的唯象蠕变模型的一个关键限制是岩盐的各向异性响应没有在微观结构水平上表示。 虽然晶体塑性模型捕捉各向异性在岩盐确实存在，他们采用经验的流量方程，这是有效的温度和应变速率范围很窄。 目前，有一个明显的缺乏晶体取向敏感的模型在文献中的蠕变和断裂的三维岩石标本耦合的直接测量的三维晶体结构。因此，这项研究将结合联合收割机无损三维X射线衍射（3DXRD），三维同步微计算机断层扫描（SMT）原位实验测量，和三维晶体塑性建模，以提高目前的蠕变和裂纹的形成和生长机制在多晶岩石的理解是前所未有的在许多方面。 最近，PI证明了在岩石微观结构内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一个更丰富的数据集校准的微观结构本构模型占各向异性。 通过采用位错机制为基础的晶体塑性模型，我们计划阐明的管理机制，产生所观察到的蠕变和断裂响应的岩盐晶体。

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.