52 research outputs found
Unravelling effects of pore-size correlation length on two-phase flow and transport properties
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Upscaling Hydrodynamic Dispersion in non‐Newtonian Fluid Flow through Porous Media
Get PDFHydrodynamic dispersion in flow through porous media is an essential phenomenon in many geosystems. While dispersion in flow of Newtonian fluids is relatively well-understood, many subsurface applications, such as groundwater remediation, use the flooding system with non-Newtonian fluids, such as polymer oxidants. Despite its significance, however, very limited studies have been carried out focusing on hydrodynamic dispersion in flow of non-Newtonian fluids. The present study addresses a fundamental question regarding how solute transport in flow of non-Newtonian fluids in porous media differs from the Newtonian limit. We report on the results of an extensive pore-scale study of upscaling of advection-diffusion in flow of a non-Newtonian, shear-thinning fluid through disordered and spatially-correlated porous media, using an advanced GPU-based pore-scale simulator, in order to delineate effects of the fluid’s rheology, dynamics of fluid flow, and pore-scale spatial correlations on hydrodynamic dispersion. The simulations indicate a surprising non-monotonic relation between the injection rate (or injection velocity) and the dispersivity. While dispersivity in Newtonian fluid flow in porous media is constant in the flow regime that we study, we find, however, that the dispersivity in flow of non-Newtonian fluids is shear-dependent. This highlights the gap in the existing theories of transport through porous materials for non-Newtonian fluids, which can lead to erroneous estimates of dispersion coefficients in porous materials, when the fluid’s rheology cannot be represented by Newtonian mechanic
Kinetics of wettability alteration and droplet detachment from a solid surface by low-salinity: a lattice-Boltzmann method
No full textThe dynamics of droplet detachment from a surface is a fundamental topic studied in coating engineering, fluid mechanics, and subsurface engineering applications. This topic has direct relevance to wettability alteration using the modified ionic composition of water in contact with oil droplet, low salinity waterflooding (LSWF). Previous experimental studies of LSWF have shown a very long timescale in wettability alteration which cannot be explained using bulk diffusion coefficient. In the present study, we address both the time scale of detachment, as well as the impact of buoyancy and interfacial forces (referred to as Bond number) on droplet detachment by proposing an advanced GPU-enhanced lattice Boltzmann model. In this model, the immiscible two-phase flow has been coupled with wettability alteration due to the salinity dilution. After full validation of the model against the former experiments, a set of computational setups with distinct Bond numbers were designed to investigate the effect of interfacial tension and droplet size on the dynamics of droplet detachment. Results demonstrate that droplet detachment from a surface is not a unique function of Bond number and diffusion length scale is critical in detachment time. In summary, this study provides a fully validated model of LSWF and delineates the significant difference in impacts of interfacial tension and bubble size on detachment time, which can be used to predict capability for LSWF, to determine favorable conditions, as well as to observe and explain low-salinity-effect
Lattice-Boltzmann simulation of dissolution of carbonate rock during CO2-saturated brine injection
No full textGeological carbon sequestration is one of the few effective technologies to reduce atmospheric CO2, which is essential to reach the net zero-emission target. Both rock pore space characteristics and injected fluids control the reactions in the CO2-brine-rock system. To address the geochemical reactions in the CO2-brine-rock system, computational simulations and specifically pore-scale simulations are of great advantages to assist in-depth understanding and support the design of experiments. In this study, we have developed a lattice-Boltzmann model to investigate the pore-scale reactive transport in carbonate rocks. The proposed algorithm couples the pore-scale flow simulation, kinetic and equilibrium solid-fluid reactions by changing the solid occupancy in each grid due to the dissolution/precipitation under fixed mesh structure. Using the proposed simulator, the dynamic dissolution of calcite by HCl in a channel was simulated and compared against the experimental results based on an upscaled calcite dissolution rate and concentration profiles. After validating the model, the reactive flow in the CO2–brine–rock system was simulated and compared against the corresponding pore-scale experiments reported in the literature. Finally, the evolution of porosity and permeability with time was studied under various flow rates, pressures and temperatures of the injected CO2-dissolved brine. The pore-scale model provides extra flexibility in predictive modelling, in-depth understanding of the physical-chemical processes and can be used for assessment of the caprock integrity in the long term
Unravelling Effects of the Pore‐Size Correlation Length on the Two‐Phase Flow and Solute Transport Properties: GPU‐based Pore‐Network Modeling
No full textContinuum-scale models for two-phase flow and transport in porous media are based on the empirical constitutive relations that highly depend on the porous medium heterogeneity at multiple scales including the microscale pore-size correlation length. The pore-size correlation length determines the representative elementary volume and controls the immiscible two-phase invasion pattern and fluids occupancy. The fluids occupancy controls not only the shape of relative permeability curves but also the transport zonation under two-phase flow conditions, which results in the non-Fickian transport. This study aims to quantify the signature of the pore-size correlation length on two-phase flow and solute transport properties such as the capillary pressure- and relative permeability-saturation, dispersivity, stagnant saturation, and mass transfer rate. Given the capability of pore-scale models in capturing the pore morphology and detailed physics of flow and transport, a novel graphics processing unit (GPU)-based pore-network model has been developed. This GPU-based model allows us to simulate flow and transport in networks with multimillions pores, equivalent to the centimeter length scale. The impact of the pore-size correlation length on all aforementioned properties was studied and quantified. Moreover, by classification of the pore space to flowing and stagnant regions, a simple semianalytical relation for the mass transfer between the flowing and stagnant regions was derived, which showed a very good agreement with pore-network simulation results. Results indicate that the characterization of the topology of the stagnant regions as a function of pore-size correlation length is essential for a better estimation of the two-phase flow and solute transport properties
Lattice-Boltzmann simulation of dissolution of carbonate rock during CO2-saturated brine injection
No full textGeological carbon sequestration is one of the few effective technologies to reduce atmospheric CO2, which is essential to reach the net zero-emission target. Both rock pore space characteristics and injected fluids control the reactions in the CO2-brine-rock system. To address the geochemical reactions in the CO2-brine-rock system, computational simulations and specifically pore-scale simulations are of great advantages to assist in-depth understanding and support the design of experiments. In this study, we have developed a lattice-Boltzmann model to investigate the pore-scale reactive transport in carbonate rocks. The proposed algorithm couples the pore-scale flow simulation, kinetic and equilibrium solid-fluid reactions by changing the solid occupancy in each grid due to the dissolution/precipitation under fixed mesh structure. Using the proposed simulator, the dynamic dissolution of calcite by HCl in a channel was simulated and compared against the experimental results based on an upscaled calcite dissolution rate and concentration profiles. After validating the model, the reactive flow in the CO2–brine–rock system was simulated and compared against the corresponding pore-scale experiments reported in the literature. Finally, the evolution of porosity and permeability with time was studied under various flow rates, pressures and temperatures of the injected CO2-dissolved brine. The pore-scale model provides extra flexibility in predictive modelling, in-depth understanding of the physical-chemical processes and can be used for assessment of the caprock integrity in the long term
Effects of Wettability and Minerals on Residual Oil Distributions Based on Digital Rock and Machine Learning
Get PDFAbstractThe wettability of mineral surfaces has significant impacts on transport mechanisms of two-phase flow, distribution characteristics of fluids, and the formation mechanisms of residual oil during water flooding. However, few studies have investigated such effects of mineral type and its surface wettability on rock properties in the literature. To unravel the dependence of hydrodynamics on wettability and minerals distribution, we designed a new experimental procedure that combined the multiphase flow experiments with a CT scan and QEMSCAN to obtain 3D digital models with multiple minerals and fluids. With the aid of QEMSCAN, six mineral components and two fluids in sandstones were segmented from the CT data based on the histogram threshold and watershed methods. Then, a mineral surface analysis algorithm was proposed to extract the mineral surface and classify its mineral categories. The in situ contact angle and pore occupancy were calculated to reveal the wettability variation of mineral surface and distribution characteristics of fluids. According to the shape features of the oil phase, the self-organizing map (SOM) method, one of the machine learning methods, was used to classify the residual oil into five types, namely, network, cluster, film, isolated, and droplet oil. The results indicate that each mineral’s contribution to the mineral surface is not proportional to its relative content. Feldspar, quartz, and clay are the main minerals in the studied sandstones and play a controlling role in the wettability variation. Different wettability samples show various characteristics of pore occupancy. The water flooding front of the weakly water-wet to intermediate-wet sample is uniform, and oil is effectively displaced in all pores with a long oil production period. The water-wet sample demonstrates severe fingering, with a high pore occupancy change rate in large pores and a short oil production period. The residual oil patterns gradually evolve from networks to clusters, isolated, and films due to the effects of snap-off and wettability inversion. This paper reveals the effects of wettability of mineral surface on the distribution characteristics and formation mechanisms of residual oil, which offers us an in-deep understanding of the impacts of wettability and minerals on multiphase flow and helps us make good schemes to improve oil recovery
Transition From Viscous Fingering to Capillary Fingering: Application of GPU‐Based Fully Implicit Dynamic Pore Network Modeling
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