Significance The simultaneous flow of multiple fluid phases through a porous solid occurs in many natural and industrial processes—for example, rainwater infiltrates into soil by displacing air, and carbon dioxide is stored in deep saline aquifers by displacing brine. It has been known for decades that wetting—the affinity of the solid to one of the fluids—can have a strong impact on the flow, but the microscale physics and macroscopic consequences remain poorly understood. Here, we study this in detail by systematically varying the wetting properties of a microfluidic porous medium. Our high-resolution images reveal the fundamental control of wetting on multiphase flow, elucidate the inherently 3D pore-scale mechanisms, and help explain the striking macroscopic displacement patterns that emerge. Multiphase flow in porous media is important in many natural and industrial processes, including geologic CO2 sequestration, enhanced oil recovery, and water infiltration into soil. Although it is well known that the wetting properties of porous media can vary drastically depending on the type of media and pore fluids, the effect of wettability on multiphase flow continues to challenge our microscopic and macroscopic descriptions. Here, we study the impact of wettability on viscously unfavorable fluid–fluid displacement in disordered media by means of high-resolution imaging in microfluidic flow cells patterned with vertical posts. By systematically varying the wettability of the flow cell over a wide range of contact angles, we find that increasing the substrate’s affinity to the invading fluid results in more efficient displacement of the defending fluid up to a critical wetting transition, beyond which the trend is reversed. We identify the pore-scale mechanisms—cooperative pore filling (increasing displacement efficiency) and corner flow (decreasing displacement efficiency)—responsible for this macroscale behavior, and show that they rely on the inherent 3D nature of interfacial flows, even in quasi-2D media. Our results demonstrate the powerful control of wettability on multiphase flow in porous media, and show that the markedly different invasion protocols that emerge—from pore filling to postbridging—are determined by physical mechanisms that are missing from current pore-scale and continuum-scale descriptions.

Wettability control on multiphase flow in patterned microfluidics

To characterize the pore features of outburst coal samples and investigate whether outburst coal has some unique features or not, one of the authors, working as the member of the State Coal Mine Safety Committee of China, sampled nine outburst coal samples (coal powder and block) from outburst disaster sites in underground coal mines in China, and then analyzed the pore and surface features of these samples using low temperature nitrogen adsorption tests. Test data show that outburst powder and block coal samples have similar properties in both pore size distribution and surface area. With increasing coal rank, the proportion of micropores increases, which results in a higher surface area. The Jiulishan samples are rich in micropores, and other tested samples contain mainly mesopores, macropores and fewer micropores. Both the unclosed hysteresis loop and force closed desorption phenomena are observed in all tested samples. The former can be attributed to the instability of the meniscus condensation in pores, interconnected pore features of coal and the potential existence of ink-bottle pores, and the latter can be attributed to the non-rigid structure of coal and the gas affinity of coal.

Pore characterization of different types of coal from coal and gas outburst disaster sites using low temperature nitrogen adsorption approach

Gas diffusion in coal particles: A review of mathematical models and their applications

Advancing CO2 enhanced oil recovery and storage in unconventional oil play—Experimental studies on Bakken shales

Potential of palm kernel shell as activated carbon precursors through single stage activation technique for carbon dioxide adsorption.

Physical simulation of temperature influence on methane sorption and kinetics in coal: Benefits of temperature under 273.15 K

Temperature-dependent diffusion process of methane through dry crushed coal

Understanding the sorption behavior of gas in organic-rich sedimentary rocks and, more specifically, recognizing the adsorption properties of methane in coal and crucial steps for evaluating the coalbed methane (CBM) gas-in-place content, gas quality, and CBM recovery potential. However, the adsorption affinity of coal on methane has not been previously considered. This paper introduces the isosteric heat of adsorption in Henry’s region, renamed the mean isosteric heat of adsorption, as means to evaluate the adsorption affinity of coal on methane. 18 group isothermal adsorption tests for methane in three different coals were conducted from 243.15 to 303.15 K. The mean isosteric heat of adsorption for anthracite, lean coal, and gas-fat coal is −23.31, −20.47, and −11.14 kJ/mol, respectively. The minus signs indicate that the adsorption is an exothermal process. The mean isosteric heat of adsorption is independent of the temperature from 243.15 to 303.15 K and shows the overall heterogeneous property of dif...

Zhaofeng Wang

Papers

Pore characterization of different types of coal from coal and gas outburst disaster sites using low temperature nitrogen adsorption approach

Physical simulation of temperature influence on methane sorption and kinetics in coal: Benefits of temperature under 273.15 K

Temperature-dependent diffusion process of methane through dry crushed coal

Adsorption Affinity of Different Types of Coal: Mean Isosteric Heat of Adsorption

Influence of water invasion on methane adsorption behavior in coal