Controlling fingering instabilities

一种粘性流体被另一种流体驱替的过程和动力学无处不在，影响着涉及流体驱替的无数自然现象和技术应用。特别是，当粘性较低的流体取代另一种不混溶的流体(如水推油)时，在多孔介质或狭窄通道中的波状界面可能会发生由粘度差异引发的流体动力不稳定性。这种所谓的粘性指进不稳定会产生一个手指形状的传播锋面，将驱替的流体(例如，油)部分扫除，从而对各种技术造成不利影响。例如，众所周知，粘性指进不稳定是提高石油采收率、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，它们的粘度对比是主要决定流动不稳定性的给定因素。这一发现计划解决了这一挑战，旨在创新控制和在微观和宏观尺度上对粘性指进不稳定性进行批判性理解。我们将用一种新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理。为此，提出了三个综合项目，以使用(I)复杂流体、(Ii)微流体和(Iii)电气手段进行最先进的实验。这些项目还旨在填补文献中的关键空白，即如何从宏观上控制锥形单元中复杂的粘性指进，在非均质孔结构中控制复杂的粘性指进，以及在外部电气手段下控制复杂粘性指进。有了这些新颖的实验配置，几个HQP(高素质人员)将对较低粘度的流体置换更粘性、更复杂的流体的界面轮廓和回收率进行高分辨率测量。得到的定量结果包括不同流量下的时变界面分布和采收率，从而得到了复杂流体稳定和不稳定粘性指进的重要相图，与简单的牛顿流体相比，很少有人研究这些相图。我们将通过实验阐明如何控制多孔介质中复杂流体的粘性指进不稳定性的机理和技术。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、含盐含水层的碳捕获和储存、层析技术、膜应用和地下水技术的各种应用。

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.