Controlling fingering instabilities

粘性流体被另一种流体驱替的过程和动力学是无所不在的，影响着无数的自然现象和涉及流体驱替的技术应用。特别是，当粘度较低的流体取代另一种不混相的流体（如水推油）时，由粘度对比引发的流体动力学不稳定性可能在多孔介质或狭窄通道中的波浪界面中发生。这种所谓的粘性指向不稳定性会产生一个手指状的传播前缘，并导致部分被驱替的流体（如石油）被扫过，从而对各种技术产生不利影响。例如，粘性指指不稳定性是提高采收率、地下水技术和印刷工艺的关键限制因素。然而，由于流体通常是预先选定的，因此它们的粘度对比是决定流动不稳定性的一个给定因素，因此控制粘性指指不稳定性是困难和具有挑战性的。这个发现计划解决了这一挑战，旨在创新控制和对微观和宏观尺度上的粘性指法不稳定性的批判性理解。我们将用一种新颖的方法进行微流控和大规模实验，以阐明流体之间界面轮廓的动力学和机制。为此目的，提出了三个综合项目，利用（一）复杂流体、（二）微流体和（三）电气手段开展最先进的实验。这些项目还旨在填补文献中关于如何在宏观上、在非均质孔隙结构中以及在外部电手段下分别控制锥形细胞中复杂粘性指指的关键空白。有了这些新颖的实验配置，几个hqp（高素质的人员）将对低粘性流体取代高粘性复杂流体的界面剖面和采收率进行高分辨率测量。获得的定量结果包括不同流量下随时间变化的界面轮廓和采收率，因此，对于复杂流体来说，稳定与不稳定粘性指指的重要相图，与简单的牛顿流体相比，很少进行探索。我们将通过实验来阐明其机理和如何控制多孔介质中复杂流体的粘性指指不稳定性。我们将应用该项目中获得的新见解来帮助改善复杂粘性流体的不利部分波及和采收率。预期的结果将有利于石油和天然气行业的各种应用，包括含盐含水层的碳捕获和储存、色谱技术、膜应用和地下水技术。

The process and dynamics of a viscous fluid displaced by another are omnipresent, affecting a myriad of both natural phenomena and technological applications involving fluid--fluid displacement. In particular, when a less viscous fluid displaces another immiscible one (such as water pushing oil), a hydrodynamic instability triggered by a viscosity contrast can occur with a wavy interface in a porous medium or narrow passage. This so--called viscous fingering instability produces a finger--shaped propagation front with a partial sweep of the displaced fluid (e.g., oil), thereby detrimentally hampering a variety of technologies. For example, the viscous fingering instability is notoriously a critical limiting factor for enhanced oil recovery, groundwater technologies, and printing processes, to name a few. The control of viscous fingering instability is, however, difficult and challenging because the fluids are often pre--selected and, hence, their viscosity contrast is a given factor that predominately determines the flow instabilities. This Discovery program tackles this challenge and aims at both innovative control and critical understanding of the viscous fingering instability at both micro- and macro--scales. We will conduct both microfluidic and large--scale experiments with a novel approach to elucidate the dynamics and mechanism of the interfacial profiles between the fluids. To this end, three comprehensive projects are proposed to carry out state--of--the--art experiments using (i) complex fluids, (ii) microfluidics, and (iii) electrical means. These projects also aim to fill the crucial gaps in the literature regarding how to control complex viscous fingering in a tapered cell macroscopically, in heterogeneous pore--structures, and under external electrical means, respectively. With these sets of novel experimental configurations, several HQPs (highly qualified personnel) will carry out high--resolution measurements of the interfacial profile and recovery rate for a less viscous fluid displacing a more viscous, complex fluid. The quantitative results obtained include time--varying interfacial profiles and recovery rates under different flow rates and, hence, the important phase diagram of stable vs. unstable viscous fingering for complex fluids, which are rarely explored comparing to simple, Newtonian fluids. We will elucidate the mechanisms and know--how on how to control the viscous fingering instability for complex fluids in porous media with experiments. We will apply new insights gained in this program to help to improve the disadvantageous partial sweep and recovery of complex viscous fluids. The expected results will benefit various applications for the oil and gas industry, carbon capture and storage in saline aquifers, chromatography technologies, membrane applications, and groundwater technologies.