In-situ X-ray Tomography and Chemical Tracer Experiments Examining Hydrothermal Alteration of Peridotite: Pore Scale Studies with Implications for Water-Rock Interaction Models

原位 X 射线断层扫描和化学示踪实验检查橄榄岩的热液蚀变：孔隙尺度研究及其对水-岩石相互作用模型的影响

• 批准号: 1426695
• 负责人: William Seyfried
• 金额: $ 25.14万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-07-15 至 2019-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1426695&HistoricalAwards=false
• 关键词: situ; ray; Tomography; Chemical; Tracer

The porosity and permeability of rocks is impacted heavily by reactions between minerals and through-going fluids. The resulting dissolution of minerals that are unstable at the temperature, pressure, and chemical conditions at which the fluids and rocks are interacting and the precipitation of more stable mineral species in the pores, fractures, and grain boundaries between minerals controls where and how much porosity a rock has and how easily fluids can flow through it. This research uses novel, flow-through, hydrothermal, reactor vessels where changes in the porosity and permeability of rocks and the precipitation and dissolution of minerals can be observed and measured in real time. Results of these experiments will be analyzed using a mathematical technique (i.e., Lattice-Boltzmann approach) that provides a better simulation of the fine-scale processes than mathematical techniques presently used in water-rock interaction studies that depend solely on continuum conditions. Intact cores of classic seafloor peridotites, rocks that commonly host or are the source of sulfide-rich, hydrothermal deposits on the seafloor, will be used in the experiments; and alteration of the original mineralogy will be tracked using the stable isotopes of Ca, Mg, and Si, which will document reactions and reaction rates of carbonate and silicate minerals. Broader impacts of the work include improving infrastructure for science by developing new experimental and mathematical methods to advance studies of water-rock interaction and how the porosity and permeability of geological materials change as rocks and sediments react with waters flowing through them. The research has significant potential applications in improving our understanding of the behavior of carbon sequestration reservoirs, the migration of pollutants, and the conditions of nuclear waste disposal. The project also involves undergraduate students from the National Science Foundation Research Experience for Undergraduates (NSF-REU) program in cutting-edge science; trains a graduate student and a postdoc; and helps to develop and verify theoretical and model simulations use to predict the chemical and physical property evolution of natural rocks and fluids.This research focuses on understanding the hydrolysis and carbonation of mantle peridotite by through-going aqueous fluids, an important process affecting the geochemical and geophysical properties of the ocean crust at mid-ocean ridges and in subduction zones. Reactions will be examined using coupled experimental, analytical, and theoretical approaches that emphasize the time series monitoring of the chemical and physical evolution of peridotite-fluid systems using a novel flow-through hydrothermal reactor and transparent reaction cells that are coupled to an X-ray Computed Tomography instrument that allows changes in mineral dissolution and precipitation processes to be examined in real time and in high resolution. This allows direct investigation of changes in the 3D architecture of the rock on a fine scale during water-rock interaction. Chemical tracers using non-traditional stable isotopes (Si, Mg and Ca) will be used to constrain mineral dissolution and precipitation rates and indicate changes in mineral surface area. The experiments and their results will be modeled using a Lattice-Boltzmann multicomponent, multiphase, fluid flow and solute transport computer code with the results being used to develop more accurate reservoir-scale modeling approaches using continuum-scale simulators. Goals of the research are to investigate the feedback between fluid-mineral reactions and associated pore-space geometry changes in peridotites that result from processes like fluid flow, advection of chemical species, and reaction locations and reaction rates. Samples will consist of cores of seafloor peridotite.

岩石的孔隙度和渗透率受矿物和流体之间的反应的影响很大。在流体和岩石相互作用的温度、压力和化学条件下不稳定的矿物的溶解，以及更稳定的矿物物种在孔隙、裂缝和矿物之间的晶界中的沉淀，控制着岩石的孔隙度和孔隙度的大小，以及流体流过岩石的容易程度。反应器容器，其中可以真实的时间观察和测量岩石的孔隙度和渗透率以及矿物的沉淀和溶解的变化。这些实验的结果将使用数学技术（即，格子玻尔兹曼方法），提供了一个更好的模拟精细尺度的过程比目前使用的数学技术在水-岩相互作用的研究，只依赖于连续条件。实验中将使用典型海底橄榄岩的完整岩心，这些岩石通常是海底富含硫化物的热液矿床的宿主或来源;将使用Ca、Mg和Si的稳定同位素跟踪原始矿物学的变化，这将记录碳酸盐和硅酸盐矿物的反应和反应速率。这项工作的更广泛影响包括通过开发新的实验和数学方法来改善科学基础设施，以推进水-岩石相互作用的研究，以及地质材料的孔隙度和渗透率如何随着岩石和沉积物与流经它们的沃茨的反应而变化。 该研究在提高我们对碳封存库行为、污染物迁移和核废料处置条件的理解方面具有重要的潜在应用价值。该项目还涉及来自国家科学基金会本科生研究经验（NSF-REU）计划的本科生在尖端科学;培训研究生和博士后;并有助于发展和验证用于预测天然岩石和流体的化学和物理性质演化的理论和模型模拟。本研究的重点是了解地幔橄榄岩通过-这是一个影响洋中脊和俯冲带洋壳地球化学和地球物理特性的重要过程。反应将使用耦合实验，分析和理论的方法，强调橄榄岩流体系统的化学和物理演化的时间序列监测，使用一种新的流动通过水热反应器和透明的反应细胞，耦合到X射线计算机断层扫描仪，允许矿物溶解和沉淀过程的变化被检查在真实的时间和高分辨率。 这允许在水-岩石相互作用期间在精细尺度上直接调查岩石的3D结构的变化。使用非传统稳定同位素（Si、Mg和Ca）的化学示踪剂将用于限制矿物溶解和沉淀速率，并指示矿物表面积的变化。实验及其结果将使用格子玻尔兹曼多组分，多相，流体流动和溶质输运计算机代码建模，其结果用于开发更准确的连续尺度模拟器的小行星尺度建模方法。该研究的目标是调查流体矿物反应和相关的孔隙空间几何形状的变化，如流体流动，化学物质的平流，反应位置和反应速率的过程中产生的橄榄岩之间的反馈。样品将包括海底橄榄岩的岩芯。