Deng Hang, Peters Catherine A
Department of Civil and Environmental Engineering, Princeton University, Princeton, New Jersey.
Environ Eng Sci. 2019 Jan 1;36(1):90-101. doi: 10.1089/ees.2018.0244. Epub 2019 Jan 18.
Underground fractures serve as flow conduits, and they may produce unwanted migration of water and other fluids in the subsurface. An example is the migration and leakage of greenhouse gases in the context of geologic carbon sequestration. This study has generated new understanding about how acids erode carbonate fracture surfaces and the positive feedback between reaction and flow. A two-dimensional reactive transport model was developed and used to investigate the extent to which geochemical factors influence fracture permeability and transmissivity evolution in carbonate rocks. The only mineral modeled as reactive is calcite, a fast-reacting mineral that is abundant in subsurface formations. The X-ray computed tomography dataset from a previous experimental study of fractured cores exposed to carbonic acid served as a testbed to benchmark the model simulation results. The model was able to capture not only erosion of fracture surfaces but also the specific phenomenon of channelization, which produces accelerating transmissivity increase. Results corroborated experimental findings that higher reactivity of the influent solution leads to strong channelization without substantial mineral dissolution. Simulations using mineral maps of calcite in a specimen of Amherstburg limestone demonstrated that mineral heterogeneity can either facilitate or suppress the development of flow channels depending on the spatial patterns of reactive mineral. In these cases, fracture transmissivity may increase rapidly, increase slowly, or stay constant, and for all these possibilities, the calcite mineral continues to dissolve. Collectively, these results illustrate that fluid chemistry and mineral spatial patterns need to be considered in predictions of reaction-induced fracture alteration and risks of fluid migration.
地下裂缝充当流动通道，可能导致地下水中和其他流体出现不必要的运移。一个例子是地质碳封存背景下温室气体的运移和泄漏。本研究对酸如何侵蚀碳酸盐岩裂缝表面以及反应与流动之间的正反馈有了新的认识。开发了一个二维反应输运模型，用于研究地球化学因素对碳酸盐岩裂缝渗透率和 transmissivity 演化的影响程度。唯一被模拟为反应性的矿物是方解石，它是一种反应迅速且在地下地层中大量存在的矿物。先前对暴露于碳酸的岩心进行实验研究获得的 X 射线计算机断层扫描数据集用作基准来检验模型模拟结果。该模型不仅能够捕捉裂缝表面的侵蚀，还能捕捉导致 transmissivity 加速增加的通道化这一特定现象。结果证实了实验发现，即进水溶液的较高反应性会导致强烈的通道化而无大量矿物溶解。使用阿姆赫斯特堡石灰岩标本中方解石矿物图进行的模拟表明，矿物非均质性根据反应性矿物的空间模式既可能促进也可能抑制流动通道的发育。在这些情况下，裂缝 transmissivity 可能迅速增加、缓慢增加或保持不变，并且对于所有这些可能性，方解石矿物都持续溶解。总体而言，这些结果表明，在预测反应引起的裂缝变化和流体运移风险时需要考虑流体化学和矿物空间模式。 （注：这里 transmissivity 未找到确切中文对应词汇，保留英文）
