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We propose a simple microfluidic approach: Dissolution-After-Precipitation (DAP), to investigate regimes of carbonate rock dissolution and multiphase reactive transport. In this method, a carbonate porous medium is created in a glass microchannel via calcium carbonate precipitation, after which an acid is injected into the channel to dissolve the precipitated porous medium. Utilizing the DAP method, for the first time we realized all five classical single-phase carbonate rock dissolution regimes (uniform, compact, conical, wormhole, ramified wormholes) in a microfluidic chip. The results are validated against the established theoretical dissolution diagram, which shows good agreement. Detailed analysis of these single-phase dissolutions suggests that the heterogeneity of the porous medium may significantly impact how the dissolution patterns evolve over time. Furthermore, DAP is utilized to investigate multiphase dissolution. As examples we tested the cases of an oleic phase (tetradecane) and a gaseous phase (CO2). Results show that the presence of a nonaqueous phase in pore spaces induces the formation of wormholes despite weak advection, and these wormholes ultimately become pathways for nonaqueous phase transport. However, the transport of tetradecane in the wormhole is very slow, causing acid breakthrough into neighboring regions. This mechanism enhances lateral connectivity between wormholes and may lead to a wormhole network. In contrast, CO2 moves rapidly and continuously seeks to enter a widening wormhole from a narrower wormhole or the porous regions, generating phenomena such as ganglia redistribution and counterflow (flow of gas opposite to acid flow). Extensive independent experiments are conducted to verify the reproducibility of the observed phenomena/mechanisms and further analyze them. Real-time monitoring of fluid pressure drop during dissolution is implemented to complement microscopy image analysis. Our method can be implemented repeatedly on the same chip, which offers a convenient and inexpensive option to study pore-scale reactive transport mechanisms. [ABSTRACT FROM AUTHOR]

Geometric straining of particles in porous media is of critical importance in a broad range of natural and industrial settings, such as contaminant transport in aquifers and the permeability decline due to pore plugging in oil reservoirs. Pore network modeling is a computationally efficient approach to simulate transport problems in porous media that has been used to simulate particle deposition and size exclusion. However, existing network models are unable to simulate particle jamming due to the simplification of geometry and the lack of capability for simulating particle–particle interactions. Here, we develop a novel pore network model for particle jamming in porous media. The jamming in pore throats is predicted by the probability of jamming, which is a function of pore/particle size ratio, particle concentration, and coefficient of friction (COF). A unified probability model is developed based on Discrete Element Method (DEM) simulations of particle jamming in porous media consisting of a single layer of spherical grains. The geometry is based on two packing extremes, those with grains arranged in a triangle and a square. The model is then implemented into the pore network model to predict jamming in porous media. This framework combines the efficiency of network modeling and the accuracy of direct simulations on particle jamming. We verify the model against CFD-DEM simulations. The results of network simulations show that the probability of jamming increases with COF. At low particle concentrations (C = 5%), the probability of jamming for large pore throats is small. There is a critical particle concentration (C = 9%) when the grain/particle size ratio is 10, above which jamming is self-reinforcing and the inlet face of the porous medium will be completely blocked (C = 11%). The effect of velocity on the probability of jamming is insignificant compared with the effects of particle concentration and pore/particle size ratio. Article Highlights: We propose a novel pore network model for particle jamming based on the probability. The pore network model has a higher computational efficiency, compared with other numerical models, such as CFD-DEM model. The pore network model can accurately predict the permeability changes of porous media during the jamming process. [ABSTRACT FROM AUTHOR]

Preferential flow that leads to non-uniform displacement, especially in heterogeneous porous media, is usually unwelcome in most practical processes. We propose a self-adaptive preferential flow control mechanism by using dispersed polymers, which is supported strongly by experimental and numerical evidence. Our experiments are performed on a microchip with heterogeneous porous structures where oil is displaced by dispersed polymer microsphere particles. Even though the size of the particles is much smaller than the pore-throat size, the diversion effect by the dispersed microspheres is still proved. Therefore, the plugging effect is not the major mechanism for preferential flow control by dispersed polymers. The mechanisms are further investigated by pore-scale modelling, which indicates that the dispersed polymers exhibit an adaption ability to pressure and resistance in the porous flow field. In such an intelligent way, the displacing fluid with dispersed polymers smartly controls the preferential flow by inducing pressure fluctuations, and demonstrates better performance in both efficiency and economic aspects than the traditional method by simply increasing the viscosity. These insights can be applied to improve techniques in the field, such as enhanced oil recovery and soil wetting. [ABSTRACT FROM AUTHOR]

Transport and filtration of micron and submicron particles in porous media is important in applications such as water purification, contaminants dispersion, and drilling mud invasion. Existing macroscopic models often fail to be predictive without empirical adjustments and a more fundamental approach may be required. We develop a physically-representative, 3D pore network model based on a particle tracking method to simulate particle retention and permeability impairment in polydisperse particle systems. The model includes the effect of hydraulic drag, gravity, electrostatic and van der Waals forces, as well as Brownian motion. A converging-diverging pore throat geometry is used to capture the mechanism of interception. With the analytical solution of fluid velocity within a pore throat, the trajectory of each particle is calculated explicitly. We also incorporate surface roughness and particle-surface interaction to determine particle attachment and detachment. Pore throat structure and conductivity are updated dynamically to account for the effect of deposited particles. Predictions of effluent concentration and macroscopic filtration coefficient are in good agreement with published experimental data. We find that the filtration coefficient is dependent on the relative angle between fluid flow and gravity. Particle deposition by interception is significant for large particle/grain size ratios. Brownian diffusion is the primary cause of retention at low Peclet numbers, especially for small gravity numbers. Particle size distribution is found to be a cause of hyperexponential deposition often observed in experiments. Permeability reduction was small for strong repulsive forces because particles only deposited in paths of slow velocity. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3118-3131, 2017 [ABSTRACT FROM AUTHOR]

• Modeling of tracer transport in two-phase flow in capillary-dominated porous media. • Hydrodynamic dispersion, partition coefficient, and solute adsorption are examined. • Accurate modeling of tracer transfer by spontaneous imbibition in porous media. Transport of chemical tracers in porous media is an important physical mechanism for applications in oil reservoir characterization, aquifer remediation, and CO 2 storage. Although numerous analytical solutions exist to model the flow of solutes under single-phase flow, the modeling of solute transport in two-phase media driven by imbibition has been insufficiently examined. In tight porous media and the matrix of fractured reservoirs, spontaneous imbibition (SI) represents a key driving mechanism for fluid infiltration because the low permeability in these systems results in negligible transport by advection. Here, we present a new semi-analytical solution to model the transport of chemical tracers under one-dimensional countercurrent SI in oil–water porous media. The model presented is derived from the analysis of fluid imbibition driven by capillarity and numerically solved as a function of water distribution. We model ideal and partitioning tracers to examine the contacted region and estimate the average oil saturation in capillary-dominated media under countercurrent SI. The concentration profiles obtained with the derived model show an excellent agreement against numerical simulation results, verifying that the semi-analytical solution accurately models the mechanisms of partitioning, hydrodynamic dispersion, and adsorption. The concentration profiles exhibit a significant delay in displacement behind the imbibition front when hydrodynamic dispersion is ignored and for high partitioning coefficients, demonstrating the importance of determining these properties under two-phase flow conditions. We consider that our solution derived represents an accurate alternative to time-consuming simulations that can be extended for the analysis of tracers in fractured reservoirs to estimate oil saturation in the matrix medium. [ABSTRACT FROM AUTHOR]

Micro/nanofluidic experiments in synthetic representations of tight porous media, often referred to as “reservoir-on-a-chip” devices, are an emerging approach to researching anomalous fluid transport trends in energy-bearing and fluid-sequestering geologic porous media. We detail, for the first time, the construction of dual-scale micro/nanofluidic devices that are relatively large-scale, two-dimensional network representations of granular and fractured nanoporous media. The fabrication scheme used in the development of the networks on quartz substrates (master patterns) is facile and replicable: transmission electron microscopy (TEM) grids with lacey carbon support film were used as shadow masks in thermal evaporation/deposition and reactive ion etch (RIE) was used for hardmask pattern transfer. The reported nanoscale network geometries are heterogeneous and composed of hydraulically resistive paths (throats) meeting at junctures (pores) to mimic the low topological connectivity of nanoporous sedimentary rocks such as shale. The geometry also includes homogenous microscale grid patterns that border the nanoscale networks and represent microfracture pathways. Master patterns were successfully replicated with a sequence of polydimethylsiloxane (PDMS) and Norland Optical Adhesive (NOA) 63 polymers. The functionality of the fabricated quartz and polymer nanofluidic devices was validated with aqueous imbibition experiments and differential interference contrast microscopy. These dual-scale fluidic devices are promising predictive tools for hypothesis testing and calibration against bulk fluid measurements in tight geologic, biologic, and synthetic porous material of similar dual-scale pore structure. Applications to shale/mudrock transport studies in particular are focused on herein. [ABSTRACT FROM AUTHOR]

A novel Eulerian network model that incorporates "shear dispersion," the stretching of solute due to nonuniform velocity profiles within pore throats is developed. The superposing transport method (STM) is nonlocal in time (i.e., uses information from several previous time steps) and is equivalent to performing network-wide time convolutions of elementary throat response functions. Predicted macroscopic longitudinal dispersion coefficients for disordered sphere packs are in good agreement with published experimental data. We further investigate the impact of mixing assumptions within pores on macroscopic longitudinal dispersion and find the dependence to be weak for disordered sphere packs. Limitations of Eulerian network models as a whole are also discussed, and their inappropriateness for ordered porous media concluded. [ABSTRACT FROM AUTHOR]

Several approaches have been developed in the literature for solving flow and transport at the pore scale. Some authors use a direct modeling approach where the fundamental flow and transport equations are solved on the actual pore-space geometry. Such direct modeling, while very accurate, comes at a great computational cost. Network models are computationally more efficient because the pore-space morphology is approximated. Typically, a mixed cell method ( MCM) is employed for solving the flow and transport system which assumes pore-level perfect mixing. This assumption is invalid at moderate to high Peclet regimes. In this work, a novel Eulerian perspective on modeling flow and transport at the pore scale is developed. The new streamline splitting method ( SSM) allows for circumventing the pore-level perfect-mixing assumption, while maintaining the computational efficiency of pore-network models. SSM was verified with direct simulations and validated against micromodel experiments; excellent matches were obtained across a wide range of pore-structure and fluid-flow parameters. The increase in the computational cost from MCM to SSM is shown to be minimal, while the accuracy of SSM is much higher than that of MCM and comparable to direct modeling approaches. Therefore, SSM can be regarded as an appropriate balance between incorporating detailed physics and controlling computational cost. The truly predictive capability of the model allows for the study of pore-level interactions of fluid flow and transport in different porous materials. In this paper, we apply SSM and MCM to study the effects of pore-level mixing on transverse dispersion in 3-D disordered granular media. [ABSTRACT FROM AUTHOR]

A conference paper about the use of physically representative pore-scale network model for non-Darcy flow in porous media is presented. It notes that the quantitative and predictive results of the study are gathered using computer-generated porous media and real sandstones digitized through x-ray computed microtomography (XMT). It relates that the validity of Forchheimer's equation, which includes a quadratic correction to Darcy's Law, is determined using network simulations.

Countercurrent spontaneous imbibition (SI) is an important flow mechanism to recover oil in water-wet porous media through capillarity. Experimental imbibition tests conducted in core samples show that oil recovery as a function of time occurs in a characteristic S-shaped curve, which describes the infinite-acting and the boundary-dominated regime. Although several dimensionless time groups have been proposed to model countercurrent SI in porous media, they fail to properly scale the results, causing inaccurate estimates of oil recovery. In this work, we present a new approach, using a hybrid solution, to model countercurrent SI for oil-water systems dominated by capillary forces. The infinite-acting regime is modeled by an early-time solution using a new dimensionless time group, which enables the correct scaling of imbibition results onto a universal single curve. To model the boundary-dominated regime, we introduce a late-time solution derived as a function of a characteristic distribution of saturation to estimate the flow behavior after the imbibing fluid reaches the no-flow boundary. The novelty of the model is that it enables the accurate estimation of fluid imbibition under the boundary-dominated regime, a flow condition critical to evaluate the true potential of countercurrent SI driven by capillarity for oil recovery in porous media. We verified the model against numerical simulations under a wide range of flow conditions relevant in water-oil systems, and used experimental data reported in the literature to validate our model. The solution presented provides an accurate approach to model countercurrent SI, which could be extended for dynamic conditions and the modeling of the flow of fluids in fractured media. • Countercurrent SI can be used as an oil recovery mechanism in porous media. • A hybrid solution is introduced to model countercurrent SI at early and late times. • Early-time imbibition results collapse onto a universal single curve. • A new dimensionless time group is introduced to scale countercurrent SI results. [ABSTRACT FROM AUTHOR]

Network modeling is a useful tool for investigating pore-scale behavior and in some cases for determining macroscopic information such as permeability, relative permeability, and capillary pressure. Physically representative network models are particularly useful because quantitative and predictive results can be obtained. In the past, network models have been used as stand-alone tools for predicting flow behavior at the pore scale. In these cases, simple boundary conditions such as a pressure gradient in one direction are generally imposed on the network. However, with the increasing emphasis on multiscale modeling techniques, the real potential of network models is as a bridge from the pore to the continuum scale. In this context, continuum-scale and pore-scale models are used jointly; pore-scale behavior is upscaled and substituted into a continuum-scale simulator. Methods for integrating these techniques are being developed, and one important question is how to match boundary conditions for the two scales. In this work, physically representative network models created from computer-generated sphere packings are coupled to adjacent continuum-scale models. By coupling the two regions, realistic boundary conditions are enforced, which reflect the heterogeneity of the packed bed as well as the resistance of the adjacent medium. Results of the direct coupling show that both pore-scale phenomena and macroscopic behavior (such as flowrate) are significantly different than when these same parameters are obtained by implementing simple (decoupled) boundary conditions. [Copyright &y& Elsevier]

The dynamic behavior of microemulsion-forming water-oil-amphiphiles mixtures is investigated in a 2.5D micromodel. The equilibrium phase behavior of such mixtures is well-understood in terms of macroscopic phase transitions. However, what is less understood and where experimental data are lacking is the coupling between the phase change and the bulk flow. Herein, we study the flow of an aqueous surfactant solution--oil mixture in porous media and analyze the dependence of phase formation and spatial phase configurations on the bulk flow rate. We find that a microemulsion forms instantaneously as a boundary layer at the initial surface of contact between the surfactant solution and oil. The boundary layer is temporally continuous because of the imposed convection. In addition to the imposed flow, we observe spontaneous pulsed Marangoni flows that drag the microemulsion and surfactant solution into the oil stream, forming large (macro)emulsion droplets. The formation of the microemulsion phase at the interface distinguishes the situation from that of the more common Marangoni flow with only two phases present. Additionally, an emulsion forms via liquid-liquid nucleation or the Ouzo effect (i.e., spontaneous emulsification) at low flow rates and via mechanical mixing at high flow rates. With regard to multiphase flow, contrary to the common belief that the microemulsion is the wetting liquid, we observe that the minor oil phase wets the solid surface. We show that a layered flow pattern is formed because of the out-of-equilibrium phase behavior at high volumetric flow rates (order of 2 m/day) where advection is much faster than the diffusive interfacial mass transfer and transverse mixing, which promote equilibrium behavior. At lower flow rates (order of 30 cm/day), however, the dynamic and equilibrium phase behaviors are well-correlated. These results clearly show that the phase change influences the macroscale flow behavior. [ABSTRACT FROM AUTHOR]

Multiphase displacements in porous media are expected to be stable if the injectant has a smaller mobility than the resident phase and injection velocity is small. We investigate two-phase displacements (aqueous phase displacing oleic phase) at favorable mobility ratios, which are expected to be stable, and find that the presence of low-viscosity irreducible water promotes the formation of viscous instabilities. Microfluidic experiments and Lattice Boltzmann (LB) simulations were utilized to identify the effects of pore-scale mobilization of irreducible water on centimeter-scale flow patterns during favorable displacements. Displacements in glass micromodels showed the presence of low viscosity irreducible water resulted in fingering and early breakthrough compared to experiments with high viscosity irreducible water (glycerol solution). The LB simulations were used to explain that fingers formed because irreducible water was mobilized ahead of the injected water. The low viscosity aqueous front fingered through the oil as the viscosity of the oil was larger than that of the low viscosity aqueous phase bank. Additionally, we conducted a coreflood that showed breakthrough of the aqueous phase occurred slightly earlier when irreducible aqueous phase viscosity was low (1 cp) than when irreducible aqueous phase viscosity was large (69 cp). The novelty of this work lies in showing that presence of low viscosity irreducible water may result in an unstable displacement of medium viscosity oil by high viscosity aqueous solution at small flooding velocities. [ABSTRACT FROM AUTHOR]