Multiscale modelling of miscible interfaces: Application on surfactant-enhanced aquifer remediation

通过在注射溶液中应用表面活性剂的原位化学增强增溶是回收这些污染物的有前途的方法。然而，该过程涉及相边界的动态演化，以及相互作用的多种驱动力，包括毛细管力和粘性力。一方面，量化NAPL恢复的主要机制的贡献（通过降低界面张力和增强溶解NAPL神经节的动员），需要集成的基本物理接口与连续尺度预测工具。另一方面，跨越多孔介质的多个长度尺度的纹理不均匀性使预测污染物物种的迁移路径变得复杂，影响置换机制，并增加了修复操作在回收效率方面的成功的不确定性。尽管积累的兴趣在建模的过程中，涉及动态演变的接口和基础科学的混相驱，通过计算流体动力学（CFD）的最新进展，微流体研究，微观模型实验和热力学的接口，多尺度异质性的影响NAPL恢复的机制还没有被系统地量化。因此，我们的总体目标是通过设计一种新的多尺度计算装置，集成了表面活性剂增强含水层修复的背景下，混溶位移的动态，以解决纳入微观和宏观的非均质性的多孔系统。在WP 1中，我们数值上进行了达西尺度的相互作用的驱动力的无量纲分析。特别是，我们将利用无量纲的数字，包括达姆克勒数（代表质量转移平流比），佩克莱数，粘度比，和地质统计参数的绝对渗透率分布，如空间相关长度。我们构建了一个流态图，并描绘相互作用的粘性和化学溶解锋煽动的程度，分别由流体之间的粘度差和渗透率反馈机制。我们展示了渗透率非均质性（以各种形式，如渠道化河流系统，长空间相关分布，高斯渗透率实现等）的相互作用。在WP 2中，我们寻求创新的孔隙网络建模，以支持在微观尺度上对驱替机制至关重要的物理过程（神经节折断和动员与相间扩散和传质）。我们使用CFD理论模型的界面演化和严格的传输模型的粘性和化学位移。我们从孔隙尺度上放大流动和输运解的结果，以获得代表性基本体积平均的多相流动和输运宏观性质。通过新的孔隙网络生成技术，我们描绘了孔隙水平统计，形态和结构对升级性能的影响，在WP 3中，我们通过一种新颖的时空自适应计算装置集成了两个尺度的建模，该装置将为确定表面活性剂效率的潜在物理现象提供独特的见解。加强含水层补救进程。除了用于含水层修复的新型多尺度工具的具体应用之外，计算装置将服务于各种工程学科的目的，例如废物处理、地质碳封存、提高石油采收率、药物递送等，其中跨动态界面的相间质量传递是普遍存在的特征。

In situ chemically enhanced solubilisation through the application of surfactants in injection solutions is a promising method to recover these contaminants. The process, nonetheless, involves dynamic evolution of phase boundaries, and multiple driving forces interacting with each other including capillary and viscous forces. On one hand, quantifying the contribution of the main mechanisms of NAPL recovery (mobilisation of NAPL ganglia through reduced interfacial tension and enhanced solubilisation), requires integration of fundamental physics of interfaces with continuum scale predictive tools. On the hand, the textural heterogeneities that span across multiple length scales of the porous medium complicates predicting the migration paths of the contaminant species, impacts the displacement mechanisms and adds uncertainty to the success of remediation operation in terms of recovery efficiency. Despite accumulated interest in modelling of the processes that involve dynamically evolving interfaces and underpinned science of miscible displacement through recent advances in Computational Fluid Dynamics (CFD), microfluidic studies, micromodel experiments and thermodynamics of interfaces, the impact of multiscale heterogeneity on the mechanisms of NAPL recovery has not been systematically quantified. Our overall aim is therefore to address incorporation of micro- and macro-heterogeneities of the porous system, by devising a novel multiscale computational apparatus that integrates dynamics of miscible displacement in the context of surfactant-enhanced aquifer remediation. In WP1 we numerically undertake a dimensionless analysis of interacting driving forces in Darcy scale. In particular we will utilise dimensionless numbers including Damköhler number (to represent mass transfer to advection ratio), Péclet number, viscosity ratio, and geostatistical parameters of the absolute permeability distribution such as spatial correlation lengths. We construct a flow-regime diagram and delineate extent of interacting viscous and chemical dissolution fronts instigated by, respectively, viscosity difference between fluids and permeability-feedback mechanism. We demonstrate the interplay of permeability heterogeneities (in various forms such as channelised fluvial systems, long spatially correlated distributions, Gaussian permeability realisations, etc.) on the interaction of viscous and chemical dissolution fingering, and overall NAPL recovery.In WP2 we seek innovative pore network modelling to underpin the physical processes (ganglia snap-off and mobilisation vs. interphase diffusion and mass transfer) that crucially shape the displacement mechanisms at microscale. We use a CFD theoretical model of interface evolution and rigorous transport model of viscous and chemical displacement. We upscale the results of flow and transport solutions from pore-scale to obtain Representative-Elementary-Volume-averaged multiphase flow and transport macroscopic properties. Through novel pore network generation techniques, we delineate the effect of pore-level statistics, morphology and structure on upscaled properties, and reduce the reliance over from commonly used empirical correlations.In WP3 we integrate the two-scales of modelling through a novel spatio-temporal adaptive computational apparatus that will provide unique insights into underlying physical phenomena that determine the efficiency of surfactant-enhanced aquifer remediation processes. Beyond the specific application of the novel multiscale tool for aquifer remediation, the computational apparatus will serve the purpose of various disciplines of engineering, such as waste treatment, geological carbon sequestration, enhanced oil recovery, drug delivery, etc. where interphase mass transfer across dynamic interfaces is a ubiquitous feature.