Transport in Porous Media最新文献

Numerical simulation can provide detailed understanding of mass transport within complex structures. For this purpose, numerical tools are required that can resolve the complex morphology and consider the contribution of both convection and diffusion. Solving the Navier–Stokes equations alone, however, neglects self-diffusion. This influences the simulated displacement distribution of flow especially in porous media at low Péclet numbers (Pe < 16) and in near-wall regions where diffusion is the dominant mechanism. To address this problem, this study uses μCT-based computational fluid dynamics (CFD) simulations in OpenFOAM coupled with the random-walk particle tracking (PT) module disTrackFoam and cross-validated experimentally using pulsed-field gradient (PFG) nuclear magnetic resonance (NMR) measurements of gas flow within open-cell foams (OCFs). The results of the multi-scale simulations—with a resolution of 130–190 µm—and experimental PFG NMR data are compared in terms of diffusion propagators, which are microscopic displacement distributions of gas flows in OCFs during certain observation times. Four different flow rates with Péclet numbers in the range of 0.7–16 are studied in the laminar flow regime within 10 and 20 PPI OCFs, and axial dispersion coefficients were calculated. Cross-validation of PFG NMR measurements and CFD-PT simulations revealed a very good matching with integral differences below 0.04%, underpinning the capability of both complementary methods for multi-scale transport analysis.

Imaging of fluid flow at the pore scale in permeable media requires high spatial resolution to observe the topology of fluid in the pore system, along with high temporal resolution to study dynamic processes. The two most popular imaging techniques in modern experiments are microfluidic device imaging and X-ray micro-computed tomography, both having significant limitations as applied to the micro-level. In particular, microfluidic experiments examine flow in quasi-2D system of pores instead of natural 3D geometry of permeable media, whereas X-ray computed tomography (reconstruction of a 3D object representation from a set of 2D projections collected at different rotation angles) is considerably slow when studying fast pore-scale events. In this work, we present a novel approach to examination of local fluid dynamics by combining traditional fast X-ray microtomography and radiographic analysis of successive projections. After initial tomographic imaging of the 3D pore structure, we perform projection-wise analysis comparing differences between two successive projections. As a result, we obtain flow visualization with time resolution determined by the projection time, which is orders of magnitude faster than standard microtomographic scan time. To confirm the effectiveness of this approach, we investigate the pore-scale mechanisms of unstable water migration that occurs during gas-hydrate formation in coal media. We first show that the displacement of brine by methane gas due to cryogenic suction can lead to multiple snap-off events of brine flow in pores. Second, we study a fast local drainage process accompanied by the formation of the gradually swelling gas bubble in the center of the pore. The measured maximum interfacial velocity in our experiments varies from 1.3 to 5.2 mm/s. We also simulate this outflow process accompanied by the bubble expansion and estimate the average brine flow rate during brine-methane displacement.

Electroosmotic flow through porous media is a crucial contemporary research field that finds its application in the areas of various engineering, geological, and biological settings. Obeying Darcy’s law for electroosmotic flow through porous media in similar lines to that of pressure-driven flow yields a very important physical property of electro-permeability. This work aims to examine the influence of wall zeta potential, Debye length, the solid particle shape, and preferential orientation on the electro-permeability tensor using multiscale homogenization methodology for a single-phase fluid flow. For determining the range of possible particle shapes from prolate-oblate ellipsoid to sphere, the parameter of aspect ratio is employed. Additionally, anisotropy ratio and tortuosity have been explored. The governing equations for this study comprise a mass continuity equation, an advection–diffusion equation, a Poisson–Boltzmann equation for electric double layer, and a Laplace equation for solving the electric field in a fully coupled manner. A two-scale computational homogenization technique is employed to model the fluid-saturated periodic media subjected to external electric effects. The finite element approach is adopted to solve the multiscale and multi-physics problem in a coupled manner. The results indicate that the electro-permeability is significantly affected by wall zeta potential, aspect ratio, and orientation of solid particles. Also, one of the major findings is that the EDL thickness has a vital effect on the electro-permeability, anisotropy ratio, and tortuosity of the porous media.

We study the formation of oil droplets from an initially trapped large oil ganglion under surfactant flooding, using a microfluidic device consisting of a two-dimensional array of regularly spaced square posts. We observe that above a critical capillary number for oil mobilization, breakage of the ganglion results in the formation of either trapped patches spanning multiple pores or numerous mobile droplets that exit the device at a velocity comparable to the average flooding fluid velocity. These mobile droplets, however, are only observed when above a secondary capillary number threshold. The formation of these droplets is found to involve the simultaneous occurrence of three different passive droplet generation mechanisms where a droplet is formed as it is pulled by perpendicular fluid flow, as it is pulled by co-axial fluid flow, and or as it splits due to collision with a post. Our results show that oil breakthroughs only occur when the oil is in the form of mobile droplets, suggesting that droplet formation can be an important condition for the mobility of residual oil in porous media. Additionally, this post-array microfluidic device can be used for the production of monodisperse droplets whose size can be controlled by the spacing of the posts.

Convective drying of porous media is central to many engineering applications, ranging from spray drying over water management in fuel cells to food drying. To improve these processes, a deep understanding of drying phenomena in porous media is crucial. Therefore, detailed simulation of multiphase flows with phase change is of great importance to investigate the complex processes involved in drying porous media. While many studies aim to access the phenomena solely by simulations, here we succeed to compare comprehensively simulations with an experimental methodology based on microfluidic multiphase flow studies in engineered porous media. In this contribution, we propose a Navier–Stokes Cahn–Hilliard model coupled with balance equations for heat and moisture to simulate the two-phase flow with phase change. The phase distribution of the two fluids air and water is modeled by the Phase-Field equation. Comparisons with experiments are rare in the literature and usually involve very simple cases. We compare our simulation with convective drying experiments of porous media. Experimentally, the interface propagation of the water–air interface was visualized in detail during drying in a structured microfluidic cell made from PDMS. The drying pattern and the drying time in the experiment are very well reproduced by our simulation. This validation will enable the application for the presented Navier–Stokes Cahn–Hilliard model in more complex cases focused more on applications, e.g., in the field of fibrous materials.

The purpose of this study is to systematically examine the basic fluid dynamics associated with a fully liquid region within a porous material. This work has come about as a result of our investigation on the ocular fluid dynamics and transport process in a partially liquefied vitreous humor. The liquid is modeled as a sphere with Stokes flow while the surrounding infinite porous region is described by Brinkman flow. The development here provides basic three-dimensional axisymmetric results on flow characterization and also serves to evaluate the limits of validity of Darcy flow analysis for the same geometry. In the Darcy flow model, the liquid region is also treated as a porous region with a much higher permeability. Therefore, both liquid and porous regions are modeled by Darcy’s law. Besides the analytical results from Brinkman–Stokes model, the simpler case of Darcy–Darcy flow for the same geometry has been provided. The results of both cases are compared and the differences between the two sets of results provide the range of validity of our computational model (Khoobyar et al. in J Heat Transf 144:031208, 2022). Some interesting fluid-dynamical aspects of the system are observed through the analysis. For the Darcy–Darcy system, the liquid region velocity is uniform throughout, as expected for potential flow. With the Brinkman–Stokes model, the liquid region has a paraboloidal profile with the maximum possible peak value of six times the far-field velocity in the porous medium. With the liquid region having a lower resistance, the flow tends to converge there for both models as it seeks the path of least resistance. As for the validation of the Darcy–Darcy model, it is a good approximation as far as the exterior flow is concerned. However, the liquid region flow profiles for the two models are different as noted. The current Brinkman–Stokes model has led to explicit analytical solutions for the flow field for both regions. This has permitted an asymptotic analysis giving deeper insight into the flow characterization.

Carbon, capture, and storage (CCS) is an important bridging technology to combat climate change in the transition toward net-zero. The FluidFlower concept has been developed to visualize and study CO₂ flow and storage mechanisms in sedimentary systems in a laboratory setting. Meter-scale multiphase flow in two geological geometries, including normal faults with and without smearing, is studied. The experimental protocols developed to provide key input parameters for numerical simulations are detailed, including an evaluation of operational parameters for the FluidFlower benchmark study. Variability in CO₂ migration patterns for two different geometries is quantified, both between 16 repeated laboratory runs and between history-matched models and a CO₂ injection experiment. The predicative capability of a history-matched model is then evaluated in a different geological setting.

Due to the high computing cost of the fine-scale compositional simulations needed to effectively model miscible CO₂ flooding, upscaling techniques are needed to approximate the behaviour of these fine-scale grids on more realistic coarse-scale models. The use of transport coefficients to better represent small-scale interactions, such as the time-dependent flux of the components within the hydrocarbon phases (molecular diffusion), and the pseudoisation of relative permeabilities to ensure the matching of large-scale effects, such as the volumetric fluxes of the phases, are two of these procedures. Most times, a mismatch between the phase fluxes of the integrated fine-scale and that of the coarse-scale is observed. By adjusting or calibrating some of the generated coarse-scale pseudo functions, such as the transport coefficients, absolute permeability, or relative permeability endpoints, the accuracy of the upscaling results can be improved. This procedure can be treated a reservoir history matching problem which is typically computationally expensive. In this study, we provide a framework for representing the dynamics of small-scale molecular diffusion and macro-scale heterogeneity-induced channelling related to miscible CO₂ displacements on upscaled coarser grid reservoir models. The method used was based on the pseudoisation of relative permeability and transport coefficients and was applied to two benchmark reservoir models from the Society of Petroleum Engineers (SPE). Our results demonstrated that using effectively calibrated transport coefficients improved the upscaling results, so that the  calculated pseudo-relative permeability functions can be ignored. We proposed a unique approach to upscaling miscible floods that utilised a genetic algorithm and a neural-network-based proxy model to minimise the associated computing cost. The data-driven approximation model considerably decreased the computing cost associated with the assisted tuning technique, and the optimisation algorithm was used to reduce the error between the predictions of the upscaled models. In conclusion, the methodology described in this study effectively captured the small- and large-scale behaviour related to the miscible displacements on upscaled coarse-scale reservoir models while reduced associated computational costs.

The study reviews the theoretical models, numerical implementation and practical applications of chloride reactive transport in concrete. Thermodynamic modeling is capable of accurately predicting chloride binding behaviors across the entire concentration range. It also considers the impact of the pH variation in the pore solution. Thus, the reactive transport model, integrating thermodynamic calculations into transport equations, can provide a more comprehensive representation of chloride ingress in concrete. Furthermore, we discuss the effects of water transport and external stresses on chloride reactive transport. In addition to the well-known advection phenomenon, water transport has the ability to alter the effective transport pathway and influence chloride binding reactions. These three influences exhibit typical temporal and spatial characteristics. Capturing the temporal and spatial characteristics in chloride reactive transport model can be achieved by continuously updating the saturation degree and chloride diffusion coefficient at each finite element mesh node. The effect of stress on chloride reactive transport can be categorized into two scenarios based on the response of transport pathway to external loads: (1) high stress levels, which result in the formation of cracks in concrete, and (2) low stress levels, where concrete remains crack-free. Quantitating the influence of stress levels on the transport pathway is crucial for simulating chloride reactive transport.