Multiphase flow in porous media is important in many natural and industrial processes, including geologic CO 2 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.porous media | capillarity | wettability | microfluidics | pattern formation M ultiphase flow in porous media is important in many natural and industrial processes, including geologic CO 2 sequestration (1), enhanced oil recovery (2), water infiltration into soil (3), and transport in polymer electrolyte fuel cells (4). Much of the research on multiphase flow in porous media has focused on the effect of fluid properties and flow conditions. Much less emphasis has been given to the fluids' affinity to the porous media (i.e., wettability), even though wettability has a profound influence on fluid-fluid interactions in the presence of a solid surface (5-7). Despite recent advances in our ability to accurately measure wettability under reservoir conditions (8, 9), and to engineer wettability in the subsurface (10-13), the complex physics of wetting continues to challenge our microscopic and macroscopic descriptions (14).Fluid-fluid displacement in the presence of a solid surface can be characterized as either drainage or imbibition, depending on the system's wettability. Drainage refers to the regime where the invading fluid is less wetting to the solid surface than the defending fluid. Imbibition refers to the opposite case, where the invading fluid is more wetting to the solid surface than the defending fluid. Drainage in porous media has been studied extensively through laboratory experiments and computer simulations (15-18), and we now have a fairly good understanding of the different displacement ...

In carbon capture and storage (CCS), CO 2 is captured at power plants and then injected underground into reservoirs like deep saline aquifers for long-term storage. While CCS may be critical for the continued use of fossil fuels in a carbon-constrained world, the deployment of CCS has been hindered by uncertainty in geologic storage capacities and sustainable injection rates, which has contributed to the absence of concerted government policy. Here, we clarify the potential of CCS to mitigate emissions in the United States by developing a storage-capacity supply curve that, unlike current large-scale capacity estimates, is derived from the fluid mechanics of CO 2 injection and trapping and incorporates injection-rate constraints. We show that storage supply is a dynamic quantity that grows with the duration of CCS, and we interpret the lifetime of CCS as the time for which the storage supply curve exceeds the storage demand curve from CO 2 production. We show that in the United States, if CO 2 production from power generation continues to rise at recent rates, then CCS can store enough CO 2 to stabilize emissions at current levels for at least 100 y. This result suggests that the large-scale implementation of CCS is a geologically viable climate-change mitigation option in the United States over the next century.carbon sequestration | pressure dissipation | residual trapping | solubility trapping C arbon dioxide is a well-documented greenhouse gas, and a growing body of evidence indicates that anthropogenic CO 2 emissions are a major contributor to climate change (1). One promising technology to mitigate CO 2 emissions is carbon capture and storage (CCS) (2-4). In the context of this study, CCS involves capturing CO 2 from the flue gas of power plants, compressing it into a supercritical fluid, and then injecting it into deep saline aquifers for long-term storage (4, 5). Compared with other mitigation technologies such as renewable energy, CCS is important because it may enable the continued use of fossil fuels, which currently supply >80% of the primary power for the planet (6, 7). We focus on CO 2 produced by power plants because electric power generation currently accounts for >40% of worldwide CO 2 emissions (8) and because power plants are large, stationary point sources of emissions where CO 2 capture technology will likely be deployed first (4). We further restrict our analysis to coal-and gas-fired power plants because they emit more CO 2 than any other type of plant: Since 2000, they have emitted ∼97% by mass of the total CO 2 produced by electricitygenerating power plants in the United States (9). We focus on storing this CO 2 in deep saline aquifers because they are geographically widespread and their storage capacity is potentially very large (4, 5).We define the storage capacity of a saline aquifer to be the maximum amount of CO 2 that could be injected and securely stored under geologic constraints, such as the aquifer's size and the integrity of its caprock. Regulatory, legal, and economic factors...

Adherent cells, crawling slugs, peeling paint, sessile liquid drops, bearings and many other living and non-living systems apply forces to solid substrates. Traction force microscopy (TFM) provides spatially-resolved measurements of interfacial forces through the quantification and analysis of the deformation of an elastic substrate. Although originally developed for adherent cells, TFM has no inherent size or force scale, and can be applied to a much broader range of mechanical systems across physics and biology. In this paper, we showcase the wide range of applicability of TFM, describe the theory, and provide experimental details and code so that experimentalists can rapidly adopt this powerful technique.

Swelling is a volumetric-growth process in which a porous material expands by spontaneous imbibition of additional pore fluid. Swelling is distinct from other growth processes in that it is inherently poromechanical: Local expansion of the pore structure requires that additional fluid be drawn from elsewhere in the material, or into the material from across the boundaries. Here, we study the swelling and subsequent drying of a sphere of hydrogel. We develop a dynamic model based on large-deformation poromechanics and the theory of ideal elastomeric gels, and we compare the predictions of this model with a series of experiments performed with polyacrylamide spheres. We use the model and the experiments to study the complex internal dynamics of swelling and drying, and to highlight the fundamentally transient nature of these strikingly different processes. Although we assume spherical symmetry, the model also provides insight into the transient patterns that form and then vanish during swelling as well as the risk of fracture during drying. arXiv:1605.00599v3 [cond-mat.soft]

Compressing a porous material will decrease the volume of the pore space, driving fluid out. Similarly, injecting fluid into a porous material can expand the pore space, distorting the solid skeleton. This poromechanical coupling has applications ranging from cell and tissue mechanics to geomechanics and hydrogeology. The classical theory of linear poroelasticity captures this coupling by combining Darcy's law with Terzaghi's effective stress and linear elasticity in a linearized kinematic framework. Linear poroelasticity is a good model for very small deformations, but it becomes increasingly inappropriate for moderate to large deformations, which are common in the context of phenomena such as swelling and damage, and for soft materials such as gels and tissues. The well-known theory of large-deformation poroelasticity combines Darcy's law with Terzaghi's effective stress and nonlinear elasticity in a rigorous kinematic framework. This theory has been used extensively in biomechanics to model large elastic deformations in soft tissues, and in geomechanics to model large elastoplastic deformations in soils. Here, we first provide an overview and discussion of this theory with an emphasis on the physics of poromechanical coupling. We present the large-deformation theory in an Eulerian framework to minimize the mathematical complexity, and we show how this nonlinear theory simplifies to linear poroelasticity under the assumption of small strain. We then compare the predictions of linear poroelasticity with those of large-deformation poroelasticity in the context of two uniaxial model problems: Fluid outflow driven by an applied mechanical load (the consolidation problem) and compression driven by a steady fluid throughflow. We explore the steady and dynamical errors associated with the linear model in both situations, as well as the impact of introducing a deformation-dependent permeability. We show that the error in linear poroelasticity is due primarily to kinematic nonlinearity, and that this error (i) plays a surprisingly important role in the dynamics of the deformation and (ii) is amplified by nonlinear constitutive behavior, such as deformation-dependent permeability.arXiv:1510.03455v3 [physics.flu-dyn]