Controlling fingering instabilities

一种粘性流体被另一种流体置换的过程和动力学是无所不在的，影响着无数涉及流体-流体置换的自然现象和技术应用。特别是，当一个较低的粘性流体取代另一个不混溶的（如水推油），流体动力学不稳定性触发的粘度对比可以发生在多孔介质或狭窄的通道中的波浪形界面。这种所谓的粘性指进不稳定性产生了指形传播前缘，其具有被驱替流体的部分扫掠（例如，石油），从而在精神上阻碍了各种技术。例如，众所周知，粘性指进不稳定性是提高石油采收率、地下水技术和印刷工艺的关键限制因素，仅举几例。然而，粘性指进不稳定性的控制是困难和具有挑战性的，因为流体通常是预先选择的，因此，它们的粘度对比度是主要决定流动不稳定性的给定因素。 这个发现计划解决了这一挑战，并在微观和宏观尺度上的粘性指进不稳定性的创新控制和批判性的理解为目标。我们将进行微流体和大规模的实验与一种新的方法来阐明流体之间的界面轮廓的动力学和机制。为此，提出了三个综合项目，以进行国家--这些项目还旨在填补文献中关于如何宏观地控制锥形单元中的复杂粘性指进、异质孔结构中的指进和外部电手段下的指进的关键空白。 有了这些新的实验配置，几个HQP（高素质的人员）将进行高分辨率的界面剖面和恢复率的测量，为较低的粘度流体取代更粘，复杂的流体。所获得的定量结果包括不同流速下随时间变化的界面剖面和采收率，因此，对于复杂流体的稳定与不稳定粘性指进的重要相图，与简单的牛顿流体相比很少被探索。本文将通过实验阐明控制多孔介质中复杂流体粘性指进不稳定性的机理和方法。我们将应用在该计划中获得的新见解，以帮助改善复杂粘性流体的不利部分波及和回收。预期的结果将有利于石油和天然气工业的各种应用，盐水层中的碳捕获和储存，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.