Evaluation of the Effects of Porous Media Structure on Mixing-Controlled Reactions Using Pore-Scale Modeling and Micromodel Experiments

Abstract

The objectives of this work were to determine if a pore-scale model could accurately capture the physical and chemical processes that control transverse mixing and reaction in microfluidic pore structures (i.e., micromodels), and to directly evaluate the effects of porous media geometry on a transverse mixing-limited chemical reaction. We directly compare pore-scale numerical simulations using a lattice-Boltzmann finite volume model (LB-FVM) with micromodel experiments using identical pore structures and flow rates, and we examine the effects of grain size, grain orientation, and intraparticle porosity upon the extent of a fast bimolecular reaction. For both the micromodel experiments and LB-FVM simulations, two reactive substrates are introduced into a network of pores via two separate and parallel fluid streams. The substrates mix within the porous media transverse to flow and undergo instantaneous reaction. Results indicate that (i) the LB-FVM simulations accurately captured the physical and chemical process in the micromodel experiments, (ii) grain size alone is not sufficient to quantify mixing at the pore scale, (iii) interfacial contact area between reactive species plumes is a controlling factor for mixing and extent of chemical reaction, (iv) at steady state, mixing and chemical reaction can occur within aggregates due to interconnected intra-aggregate porosity, (v) grain orientation significantly affects mixing and extent of reaction, and (vi) flow focusing enhances transverse mixing by bringing stream lines which were initially distal into close proximity thereby enhancing transverse concentration gradients. This study suggests that subcontinuum effects can play an important role in the overall extent of mixing and reaction in groundwater, and hence may need to be considered when evaluating reactive transport.

Pore Scale Modeling of Reactive Transport Involved in Geologic CO2 Sequestration

“…The reaction front of the large circle structure propagates much further than that of the other three porous media, and the mineral volume fraction for the horizontal ellipse structure almost coincides with that for the vertical ellipse structure. These results are quite different from those of the micromixing problem [27], where product formation is almost identical for small and large circles, but very different for the two ellipse structures. There are three reasons for this differ ence: first, the chemical reaction considered is different, while a homogeneous reaction assumed to be instantaneous is considered in the micromixing problem, in the present study, we are concerned about the heterogeneous reactions between the solution and minerals, which is treated kinetically.…”

“…Particle size and porosity are prescribed when the images are generated, and permeability is calculated using the incompressible LB model presented here. The same structures have been used in [27] to investigate the effects of porous media geometry on a transverse mixing limited chemical reaction. Unlike the micromixing problem, in our study, the structure is periodic in the y direction.…”

The Impact of Pore Structure Heterogeneity, Transport, and Reaction Conditions on Fluid–Fluid Reaction Rate Studied on Images of Pore Space

“…Willingham et al (2008) conducted micromodel experiments of bimolecular reactive transport in different porous media structures and compared it with a lattice Boltzmann model. The porous medium was a 2D system and had different pore shapes and sizes.…”

Do Current Lattice Boltzmann Methods for Diffusion and Advection-Diffusion Equations Respect Maximum Principle and the Non-Negative Constraint?

“…We consider the combined effect of transport and chemical reactions in a porous medium. Problems of this type are frequently encountered in precipitation studies and ground-water hydrology [Willingham et al, 2008]. It needs to be mentioned that Willingham et al [Willingham et al, 2008] have performed numerical modeling but employed the finite volume method for the transport problem and LBM for the flow problem.…”