Direct characterisation of transport and mixing in unsaturated porous media

不饱和多孔介质中传输和混合的直接表征

• 批准号: EP/R021627/1
• 负责人: Vahid Niasar
• 金额: $ 12.82万
• 依托单位: University of Manchester
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FR021627%2F1
• 关键词: Direct; characterisation; transport; mixing; unsaturated

Multiphase flow and hydrodynamic dispersion in porous media are the key processes in many subsurface and engineering applications, such as vadose zone contamination, soil remediation, and hydrocarbon recovery. To secure sustainable access to clean water and energy, which are identified as the global challenge areas, we urge to enhance our understanding of fundamental processes and improve our predictive capability. Hydrodynamic dispersion in porous media is controlled by the spatially and temporally variable velocity field, described by the advection-dispersion equation for saturated porous media. However, in the case of an unsaturated porous medium (where two or more immiscible fluids are present), the Fickian advection-dispersion equation is not anymore valid. In unsaturated porous media, not only the velocity field varies with the change of saturation topology, but also the spatial variation of velocity can change by orders of magnitude, such that even in homogeneous media some regions become hydrodynamically stagnant. Transport time scales in the stagnant and flowing regions can be different by orders of magnitude, which makes the concentration profiles very skewed. This feature is referred to as the non-Fickian behaviour that varies dramatically with the stagnant saturation and flow dynamics. The existing non-Fickian theories (e.g. the MIM theory) have been used to inversely model the externally-measured concentration profiles. The satisfactory "inverse modelling" results are generally regarded as an indication of the validity of these theories, although this perception has been challenged in the recent 2D micromodel experiments.In this project we articulate the major misconceptions and gaps in our understanding and we hypothesize that the concept of stagnant saturation has been incorrectly employed in the existing theories. The stagnant saturation is a two-phase flow variable, which depends on fluids topology. It should be regarded as the key "variable" to couple two-phase flow and the non-Fickian transport modelling in a hydrodynamically-consistent way, which is absent in the literature. To address the gaps and misconceptions in understanding, we have envisaged a novel experiments and modelling in two work packages (WP). In WP1, we will deliver the first direct visualisation of dispersion and mixing of a tracer in oil-wet and water-wet unsaturated porous media using the fast elapsed-time (4D) X-ray micro-tomography. All experiments will be computationally designed using the in-house developed pore-scale models and the experimental setup will be tested in Henry-Moseley X-ray Imaging Facilities. The 4D experiments are envisaged to take place in the Diamond Light Source (DLS), facilitated by the Diamond Manchester Collaboration. In WP2, the 4D X-ray images will be analysed to extract the concentration field, saturation field at different flow conditions. Transport properties including stagnant saturation, dispersion coefficient, and mass transfer rate will be quantified from the obtained images. Finally, the validity of the existing established models will be tested and a new theoretical framework will be developed. The project will benefit from the collaborations with world-renowned scientists, Prof. M. Celia (MC) from Princeton University, Prof. H. Steeb (HS) from Stuttgart University, and Prof. Brian Berkowitz (BB) from Weizmann Institute of Science and the partial support of two PhD students of the PI's team. MC will bring his key knowledge in multiphase flow and transport in porous media and their applications in large-scale problems of environmental engineering. BB has a renowned track record in mathematical analysis of non-Fickian transport in heterogeneous porous media. HS is an expert in microCT imaging of complex porous media processes and supports the WP1 by offering experimental equipment. Also, the DLS beamline scientist, Dr Nghia Vo, will support the project in data acquisition and reconstruction.

多孔介质中的多相流和流体动力学弥散是许多地下和工程应用中的关键过程，例如包气带污染、土壤修复和烃回收。为了确保可持续地获得清洁水和能源，这被确定为全球挑战领域，我们敦促加强我们对基本过程的理解，提高我们的预测能力。多孔介质中的水动力弥散由饱和多孔介质的对流弥散方程描述的时空变化的速度场控制。然而，在不饱和多孔介质（其中存在两种或更多种不混溶流体）的情况下，菲克对流-弥散方程不再有效。在非饱和多孔介质中，不仅速度场随着饱和拓扑的变化而变化，而且速度的空间变化也会发生数量级的变化，使得即使在均匀介质中，某些区域也会变得流体动力学停滞。在停滞区和流动区的传输时间尺度可以是不同的数量级，这使得浓度分布非常偏斜。该特征被称为非菲克行为，其随着停滞饱和度和流动动力学而显著变化。现有的非Fickian理论（如MIM理论）已被用来逆模型的外部测量的浓度分布。令人满意的“逆建模”的结果通常被认为是这些理论的有效性的指示，虽然这种看法已在最近的2D micromodel experiments.In这个项目中，我们阐明了我们的理解中的主要误解和差距，我们假设，停滞饱和的概念已被错误地采用在现有的理论。滞止饱和度是一个两相流变量，它取决于流体的拓扑结构。它应该被视为关键的“变量”耦合两相流和非Fickian输运模型在流体动力学一致的方式，这是缺乏在文献中。为了解决理解中的差距和误解，我们设想了两个工作包（WP）中的新实验和建模。在WP 1中，我们将使用快速流逝时间（4D）X射线显微断层扫描技术首次直接可视化示踪剂在油湿和水湿非饱和多孔介质中的分散和混合。所有实验都将使用内部开发的孔隙尺度模型进行计算设计，实验装置将在Henry-Moseley X射线成像设施中进行测试。4D实验预计将在钻石光源（DLS）中进行，由钻石曼彻斯特合作组织提供便利。在WP 2中，将对4D X射线图像进行分析，以提取不同流动条件下的浓度场、饱和度场。传输特性，包括停滞饱和度，分散系数，和传质速率将从所获得的图像进行量化。最后，现有建立的模型的有效性将进行测试，并将开发一个新的理论框架。该项目将受益于与世界知名科学家的合作，M。来自普林斯顿大学的Celia（MC）、H.来自斯图加特大学的Steeb（HS）和来自魏茨曼科学研究所的Brian Berkowitz教授（BB）以及PI团队的两名博士生的部分支持。MC将带来他在多孔介质中多相流和运输及其在环境工程大规模问题中的应用方面的关键知识。BB在非均质多孔介质中非Fickian输运的数学分析方面有着著名的记录。HS是复杂多孔介质过程microCT成像的专家，并通过提供实验设备支持WP 1。此外，DLS光束线科学家Nghia Vo博士将支持该项目的数据采集和重建。

项目成果

Direct characterization of solute transport in unsaturated porous media using fast X-ray synchrotron microtomography.

• DOI: 10.1073/pnas.2011716117
• 发表时间: 2020-09-22
• 期刊: Proceedings of the National Academy of Sciences of the United States of America
• 影响因子: 11.1
• 作者: Hasan S;Niasar V;Karadimitriou NK;Godinho JRA;Vo NT;An S;Rabbani A;Steeb H
• 通讯作者: Steeb H

Saturation Dependence of Non-Fickian Transport in Porous Media

• DOI: 10.1029/2018wr023554
• 发表时间: 2019-02-01
• 期刊: WATER RESOURCES RESEARCH
• 影响因子: 5.4
• 作者: Hasan, Sharul;Joekar-Niasar, Vahid;Sahimi, Muhammad
• 通讯作者: Sahimi, Muhammad

Coupled Processes in Charged Porous Media: From Theory to Applications

• DOI: 10.1007/s11242-019-01257-3
• 发表时间: 2019-10-01
• 期刊: TRANSPORT IN POROUS MEDIA
• 影响因子: 2.7
• 作者: Joekar-Niasar, Vahid;Schreyer, Lynn;Huyghe, Jacques
• 通讯作者: Huyghe, Jacques