Transport in Porous Media最新文献

Using extensive numerical simulation of the Navier–Stokes equations, we study the transition from the Darcy’s law for slow flow of fluids through a disordered porous medium to the nonlinear flow regime in which the effect of inertia cannot be neglected. The porous medium is represented by two-dimensional slices of a three-dimensional image of a sandstone. We study the problem over wide ranges of porosity and the Reynolds number, as well as two types of boundary conditions, and compute essential features of fluid flow, namely, the strength of the vorticity, the effective permeability of the pore space, the frictional drag, and the relationship between the macroscopic pressure gradient ({varvec{nabla }}P) and the fluid velocity v. The results indicate that when the Reynolds number Re is low enough that the Darcy’s law holds, the magnitude (omega _z) of the vorticity is nearly zero. As Re increases, however, so also does (omega _z), and its rise from nearly zero begins at the same Re at which the Darcy’s law breaks down. We also show that a nonlinear relation between the macroscopic pressure gradient and the fluid velocity v, given by, (-{varvec{nabla }}P=(mu /K_e)textbf{v}+beta _nrho |textbf{v}|^2textbf{v}), provides accurate representation of the numerical data, where (mu) and (rho) are the fluid’s viscosity and density, (K_e) is the effective Darcy permeability in the linear regime, and (beta _n) is a generalized nonlinear resistance. Theoretical justification for the relation is presented, and its predictions are also compared with those of the Forchheimer’s equation.

Colloidal transport and clogging in porous media is a phenomenon of critical importance in many branches of applied sciences and engineering. It involves multiple types of interactions that span from the sub-colloid scale (electrochemical interactions) up to the pore-scale (bridging), thus challenging the development of representative modelling. So far published simulation results of colloidal or particulate transport are based on either reduced set of forces or spatial dimensions. Here we present an approach enabling to overcome both computational and physical limitations posed by a problem of 3D colloidal transport in porous media. An adaptive octree mesh is introduced to a coupled CFD and DEM method while enabling tracking of individual colloids. Flow fields are calculated at a coarser scale throughout the domain, and at fine-scale around colloids. The approach accounts for all major interactions in such a system: elastic, electrostatic, and hydrodynamic forces acting between colloids, as well as colloids and the collector surface. The method is demonstrated for a single throat model made of four spherical segments, and the impact of clogging is reported in terms of the evolution of the critical path diameter for percolation and permeability. We identified four stages of clogging development depending on position and time of individual colloid entrapment, which in turn correlates to a cluster evolution and local transport.

Internal insulation of the building envelope is a prime topic in building physics, due to the risk of moisture problems that this technique entails. As a remedy to these problems, the application of a water-repellent agent, which reduces the amount of absorbed wind-driven rain, has become popular in recent years. When such an agent is applied on a building material, it penetrates the pore network of the material, hereby attaching itself to the pore surfaces and rendering them hydrophobic. It is generally believed that some smaller pores can remain hydrophilic due to the inability of the agent to enter. An in-depth microscopic investigation towards these hydrophilic pores, however, has never been performed. Since direct visualisation of the polymer chains was proven impossible, this paper locates the hydrophilic (parts of) pores in a material, hydrophobised with 3 different water-repellent agents, by imaging the moisture storage at pore level using X-ray computed tomography images at different stages of the desaturation process. While completely hydrophilic pore bodies and throats are not found in the studied material, water storage remains possible in hydrophilic corners of hydrophobised pore bodies and throats. These corner islands are less present than in hydrophilic media and do not form a continuous liquid flow path. Therefore, they provide possible locations for little moisture storage but do not contribute notably to moisture flow.

To meet the extensive demand for lithium (Li) for rechargeable batteries, it is crucial to enhance Li production by diversifying its resources. Recent studies have found that produced water from shale reservoirs contains various organic and inorganic components, including a significant amount of Li. In this study, findings from hydrothermal reaction experiments were analyzed to fully understand the release of Li from organic-rich shale rock. Subsequently, numerical algorithms were developed for both pore-scale and continuum-scale models to simulate the long-term behavior of Li in shale brines. The experimental conditions considered four different hydrothermal solutions, including the solutions of KCl, MgCl₂, CaCl₂, and NaCl with various concentrations under the temperature of 130 °C, 165 °C, and 200 °C. The release of Li from shale rock into fluid was regarded as a chemical interaction of cation exchange between rock and fluid. The reactive transport pore-scale and upscaled continuum-scale models were developed by coupling the chemical reaction model of Li interaction between rock and fluid. The model was first implemented to investigate the release and transport of Li in the pore scale. Continuum-scale properties, such as effective diffusivity coefficients and Li release rate, were obtained as the field-averaged pore-scale modeling results. These properties were used as the input data for the upscaled continuum-scale simulation. The findings of this study are expected to provide new insight into the production of Li from shale brines by elucidating the release, fate, and transport of Li in subsurface formations.

Colloid particle size plays an important role in contaminant adsorption and clogging in the hyporheic zone, but it remains unclear how the particle size changes during the transport of colloids. This study investigated the variation of the particle size of colloids in the overlying water and the effects of settlement and hyporheic exchange via laboratory experiments and numerical simulations with two main factors settlement and hyporheic exchange being considered. The results show that the particle size distribution varies when colloids transport in hyporheic zone, and both settlement and hyporheic exchange are involved in the exchange of colloids between stream and streambed. Large-sized particles are mainly controlled by settlement and advection and thus their concentration in the overlying water decreases more quickly; but small-sized particles are mainly controlled by hyporheic exchange and thus their concentration decreases more slowly, and some particles can be resuspended. The increase of retention coefficient and settling velocity will accelerate the transfer of colloids into the streambed. This study may provide important insights into the variation of the particle size of colloids in the overlying water and the effects of settlement and hyporheic exchange.

The pore-scale numerical modeling of CO₂ injection into natural rock saturated with oil–water mixture was performed using the density functional hydrodynamics approach. The detailed 3D digital model of the sandstone core sample contained over 7 billion cells, which allowed us to perform analysis of oil displacement efficiency at different scales. Utilization of large-size detailed numerical models make it possible to characterize, both qualitatively and quantitatively, the processes at pore scale to the level of detail not achievable on smaller models. The obtained results indicate large-scale effects even on relatively heterogeneous core indicating possible need for multiscale hierarchical models even in heterogeneous cases. This fact imposes the demand for scalability performance on both the software and hardware used in such simulations, as well as the need for adequate modeling upscaling methods.