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The pore (A) and core (B) scale flow and imaging apparatus which show how high pressure syringe pumps were connected to the flow cells to assemble the in situ experiments. In (A) CO 2 is pressurized by the injection pump and used to equilibrate brine in the reactor. Reactive brine is pulled through core assembly by the receiving pump. The cell is confined by deionized water in the confining pump and heated using heating tape controlled by a thermocouple in the confining fluid. The experimental system is connected using tubing and fluid flow is directed using Valves (V) and Unions (U). In the core-scale apparatus (B) CO 2 and brine are circulated using the bypass loop and two-phase separator to equilibrate the brine. Reactive brine is then pushed through the core assembly by the brine pumps. Pressure is measured by the pressure transducers on either side of the core and the cell is confined by deionized water in the confining pump. The entire system is heated using PID controlled heaters and thermocouples.
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We have experimentally investigated the impact of heterogeneity on the dissolution of two limestones, characterised by distinct degrees of flow heterogeneity at both the pore and core scales. The two rocks were reacted with reservoir-condition CO2-saturated brine at both scales and scanned dynamically during dissolution. First, 1 cm long 4 mm diame...
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... experimental apparatus were used to image the dynamics of dissolution in our samples. Fig. 2A depicts the apparatus used for the mm-scale experiments and Fig. 2B depicts the apparatus used for the cm-scale experiments. The Zeiss Versa XRM-500 μ-CT scanner for Ketton and the Diamond Lightsource pink beam for Portland were used to image reaction between calcite and CO 2 -saturated brine at reservoir conditions (50 °C and 10 MPa). ...
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... experimental apparatus were used to image the dynamics of dissolution in our samples. Fig. 2A depicts the apparatus used for the mm-scale experiments and Fig. 2B depicts the apparatus used for the cm-scale experiments. The Zeiss Versa XRM-500 μ-CT scanner for Ketton and the Diamond Lightsource pink beam for Portland were used to image reaction between calcite and CO 2 -saturated brine at reservoir conditions (50 °C and 10 MPa). ~1 cm length and 4 mm diameter samples were reacted by injecting ...
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... experiments were then repeated at the core scale using samples that were drilled from the same 0.04 m 3 blocks as in the pre- vious experiments. Cores of Ketton and Portland, ~8 cm long and 3.8 cm in diameter, were reacted with CO 2 saturated brine using the core-scale experimental apparatus [ Fig. 2B] by injecting pH 3.1 brine at a flow rate of 9 mL·min −1 . This flow rate was chosen to keep conditions identical by having the same amount of fluids injected per cross-sec- tional area of core [mL·m −2 ] at both experimental scales. The core- scale samples were imaged using XCT ~13 times over the course of 1.5 h with a 250 × 250 × 500 ...
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Citations
... Indeed, they are representative of the real geo-flow chemistry for a specific location. When coupled with characterization via X-rays tomography, it is possible to monitor the evolution of transient porous media characteristics in reactive flow conditions [6][7][8][9][10][11]. These experiments have been used for decades in particular by the petroleum industry to access important information on porosity, relative permeability, capillary pressure, chemistry, wettability and electrical properties of reservoirs. ...
In this study, X-ray laminography is used to monitor the evolution of a model 3D packed bed porous medium on a chip (micromodels) undergoing reactive flows. The obtained 3D images are used to compute the fluid flow patterns and develop insights into dissolution mechanisms. This study is a first proof of concept study, with controlled micromodels, and could later be extended towards deeper understanding of the dissolution and precipitation processes occurring in porous media at the microscale, mechanisms which are relevant to many industrial areas including catalysis, geochemistry, energy, and waste storage in deep geological formations, etc.
... The preferential fluid flow in inter-particle pore networks plays a crucial role in the hydraulic conduction inside unsaturated ore heaps (Wu et al., 2009;Nimmo, 2012). In four-dimensional (4-D) computed tomography (CT) (Kazantsev et al., 2015;Menke et al., 2018), the time domain is also considered, thereby realising the 3-D dynamic visualisation of the fluid flow and mass transfer inside the inter-particle pore networks. Previous experimental and computational fluid dynamics studies have found that fluid flows into heaps packed with coarse particles at higher flow velocity, while the liquid flows into heaps packed by fine feeds at lower flow velocity (McBride et al., 2012(McBride et al., , 2014(McBride et al., , 2015. ...
Due to the differences in ore feeds and stacking procedures, segregated pore networks are commonly observed in industrial heap leaching operations, which strongly affect the pore-scale fluid flow and the resulting metal leaching efficiency. Three segregated models, namely, the agglomeration model or AM with intra-particle pores, the crushed ore model or COM with inter particle pores and the mixed segregated model or MSM with both intra- and inter-particle pores, are defined in this work. The segregated pore network in the MSM consists of agglomerates and crushed particles. The models were obtained by performing micro-computed tomography scanning experiments in packed beds followed by image processing algorithms. Several fluid flow related parameters were quantified to understand the effects of segregated pore networks on fluid flow in heap leaching. The isolated and connected pores co-exist in porous ore heaps, and the latter determines heap hydrodynamics. The number of connected pores in the AM is higher than in the COM. However, the connected pores with too small pore throats are very slow in fluid transfer by capillarity, resulting in stagnant regions in ore beds. A smaller tortuosity value was also observed in the COM, resulting in fast-flowing preferential fluid flow paths. These are unfavourable to yield uniform fluid flow distributions in industrial heaps. The results of this work suggest the prerequisites for improving fluid flow distribution in heaps, including well-organised heap construction procedures, controlling the particle size distribution and large-scale studies coupled with non-invasive imaging and flow simulations.
... The pioneering study of this kind was performed by Bazin et al. (1996), however, due to technology of the time, acquisition times were long compared to wormhole growth, thus imaging was limited to only a few, low resolution, 2D scans (i.e., radiographs) through the sample. Recently, this technique has been used more frequently for wormhole studies (Ott and Oedai, 2015;Al-Khulaifi et al., 2019;Menke et al., 2018;Snippe et al., 2020), although with limited time resolution (∼30 min), and usually only a few 3D scans per experiment. By finding a compromise between the resolution and acquisition time, we are able to make a detailed, time-resolved study of growing wormholes, with as many as ∼130 (Supplementary Material, Sec. 1) scans per experiment and scan times down to five minutes. ...
... In this work we did not study large scale heterogeneities on the basis that the sample we imaged was larger than the representative elementary volume (REV) for saturation, porosity and capillary pressure (Jackson et al., 2020). The permeability can be increased significantly through dissolution or fracturing, or decreased from precipitation (Tartakovsky et al., 2007;Ellis et al., 2013;Garing et al., 2015;Menke et al., 2018). Although the impact of this is large, it is beyond the scope of this research as it creates highly transient flow. ...
Subsurface fluid flow is ubiquitous in nature, and understanding the interaction of multiple fluids as they flow within a porous medium is central to many geological, environmental, and industrial processes. It is assumed that the flow pathways of each phase are invariant when modelling subsurface flow using Darcy’s law extended to multiphase flow; a condition that is assumed to be valid during steady-state flow. However, it has been observed that intermittent flow pathways exist at steady-state, even at the low capillary numbers typically encountered in the subsurface.
In this thesis we use both laboratory-based and synchrotron-based micro-CT imaging to capture the pore-scale flow dynamics that arise when multiple fluids flow simultaneously through the pore space of a rock.
Using laboratory-based micro-CT we observed that intermittent flow pathways occur in intermediate sized pores due to the competition between both flowing fluids. This competition moves to smaller pores when the flow rate of the non-wetting phase increases. Intermittency occurs in regions where the non-wetting phase is poorly connected. Intermittency leads to the interrupted transport of the fluids; the impact on flow properties is significant because it occurs at key locations, whereby the non-wetting phase is otherwise disconnected. The amount of intermittency expected during flow is dependent on the capillary number and the viscosity ratio of the fluids.
Using fast synchrotron X-ray tomography, with 1 s time resolution, we imaged the pore-scale fluid dynamics as the macroscopic flow transitioned to steady-state, and then during steady-state. We observed distinct behaviour during transient flow, with the intermittent fluid occupancy largest and most frequent during the initial invasion into the rock. Our observations suggest that transient flows require separate modelling parameters. We observed that, during steady-state flow, intermittent fluid transport allows the non-wetting phase to flow through a more ramified network of pores. While a more ramified flow network favours lowered relative permeability, intermittency is more dissipative than laminar flow through connected pathways,
and the relative permeability remains unchanged for low capillary numbers, where the pore geometry controls the location of intermittency. As the capillary number increases further, the role of pore structure in controlling intermittency decreases, resulting in an increase in relative permeability. These observations can serve as the basis of a model for the causal links between intermittent fluid flow, fluid distribution throughout the pore space, and its upscaled manifestation in relative permeability.
... Recent advances in x-ray-CT imaging techniques [9] have enabled direct observation and quantification of dissolution-induced changes in the pore structure and provided insight into influences of structural heterogeneity, flow, and reaction rate on dissolution regime. Several experimental studies have observed mineral dissolution at the pore-scale in reservoir rock samples [10][11][12][13][14]. Others [15][16][17][18] studied the dissolution dynamics in situ during fast flow in rocks of varying complexity, observing uniform dissolution in a structurally simple rock, but the opening of preferential flow pathways in the more complex rock samples. This path-widening did not progress longitudinally with flow, as is the case for wormholes, but instead opened everywhere along the dominant flow channel and was thus named 'channeling'. ...
The current conceptual model of mineral dissolution in porous media is comprised of three dissolution patterns (wormhole, compact, and uniform) - or regimes - that develop depending on the relative dominance of flow, diffusion, and reaction rate. Here, we examine the evolution of pore structure during acid injection using numerical simulations on two porous media structures of increasing complexity. We examine the boundaries between regimes and characterise the existence of a fourth regime called channeling, where already existing fast flow pathways are preferentially widened by dissolution. Channeling occurs in cases where the distribution in pore throat size results in orders of magnitude differences in flow rate for different flow pathways. This focusing of dissolution along only dominant flow paths induces an immediate, large change in permeability with a comparatively small change in porosity, resulting in a porosity-permeability relationship unlike any that has been previously seen. This work demonstrates that our current conceptual model of dissolution regimes must be modified to include channeling for accurate predictions of dissolution in applications such as geologic carbon storage and geothermal energy production.
... The reactive transport models (RTMs) only then can provide precise and realistic predictions on the intricate interplay between transport mechanisms and reaction kinetics and, therefore, advection-diffusion-reaction (ADR). However, accurately representing the dynamics and dimensionality of mineral nucleation and growth (or, in general, ICDP) in porous media is still challenging [8,9,12,13,[23][24][25][26]. The RTM complexity arises from the ADR dependence on multiple parameters, including fluid flow, fluid chemistry, and the mineral substrate that might vary notably over different time-and length-scales [3,9,[27][28][29][30][31][32]. ...
Precipitation and growth of solid phases during a reactive fluid flow and solute transport are critical in many natural and industrial systems. Mineral nucleation and growth is a prime example where (geo)chemical reactions give rise to geometry evolution in porous media. The precipitation reactions can reduce the amount of void space, alter pore space connectivity and morphology, modify tortuosity, deteriorate permeability, and change the fluid flow and solute transport. Additionally, precipitation events reshape the available surface area for growth, leading to changes in reactivity, reaction progress, and reaction rates. The target is to ideally limit the mineral growth in many applications, such as avoiding damage to reservoir permeability due to solid precipitation near CO2 injection wells. In other cases, maximizing mineral growth in porous media can be highly favorable, such as sealing fractured caprocks or increasing mineral trapping in the sequestration sites. Understanding, controlling, and predicting this reactive transport phenomenon is challenging because it requires coupling flow, transport, and chemical processes often characterized by different temporal and spatial resolutions. Nucleation is the pre-growth process that controls the primary position of any mineral precipitation and subsequent growth dynamics. Mineral nucleation is a probabilistic process where crystals might nucleate anywhere given similar conditions, such as surface properties, supersaturation, and temperature. It is imperative to use a probabilistic approach or an upscaled physically sound representation to understand the effect of mineral precipitation on porous medium hydrodynamics. Motivated by the importance of incorporating stochastic dynamics of nucleation and growth kinetics in studying various multiphase and multiscale processes occurring in geo-environmental and geo-energy systems, this paper provides numerical and experimental insights into the recently proposed probabilistic nucleation model. We present laboratory experiments (microfluidic and flow-through column reactor) and pore-scale reactive Lattice Boltzmann Method (LBM) numerical simulations. As variations in the properties of the porous medium are intimately linked to the spatial distribution of the precipitation events, we quantify the evolution of experimental and numerical modeled systems at different physiochemical conditions by mapping the disorder of the system (Shannon's entropy) induced by the spatial mineral distributions across time. We use experimental and numerical results to show the importance of the spatial and temporal location and distribution of nucleation and growth events, particularly when the interplay among several determining parameters is inevitable. The results show that probabilistic nucleation contributes to broad stochastic distributions in both amounts and locations of crystals in temporal and spatial domains.
... The last decade has seen an explosion in the study of flow and transport behaviour at the pore-scale (Noiriel et al., 2009;Raoof et al., 2013;Varloteaux et al., 2013;Starchenko et al., 2016;Menke et al., 2017;Molins et al., 2017;Soulaine et al., 2017;Yang et al., 2020). Recent advances in X-ray imaging techniques have enabled direct observation and quantification of dissolution-induced changes in pore structures (Noiriel et al., 2009;Hao et al., 2013;Luquot et al., 2014;Menke et al., 2015Menke et al., , 2016Menke et al., , 2017Menke et al., , 2018. Numerical modeling has played an important role in these investigation of pore-scale physics, as it provides a mechanistic understanding of the relevant coupled processes. ...
We present two novel Volume-of-Solid (VoS) formulations for micro-continuum simulation of mineral dissolution at the pore-scale. The traditional VoS formulation (VoS-ψ) uses a diffuse interface localization function ψ to ensure stability and limit diffusion of the reactive surface. The main limitation of this formulation is that accuracy is strongly dependent on the choice of the localization function. Our first novel improved formulation (iVoS) uses the divergence of a reactive flux to localize the reaction at the fluid-solid interface, so no localization function is required. Our second novel formulation (VoS-ψ′) uses a localization function with a parameter that is fitted to ensure that the reactive surface area is conserved globally. Both novel methods are validated by comparison with experiments, numerical simulations using an interface tracking method based on the Arbitrary Eulerian Lagrangian (ALE) framework, and numerical simulations using the VoS-ψ. All numerical methods are implemented in GeoChemFoam, our reactive transport toolbox and three benchmark test cases in both synthetic and real pore geometries are considered: 1) dissolution of a calcite post by acid injection in a microchannel and experimental comparison, 2) dissolution in a 2D polydisperse disc micromodel at different dissolution regimes and 3) dissolution in a Ketton carbonate rock sample and comparison to in-situ micro-CT experiments. We find that the iVoS results match accurately experimental results and simulation results obtained with the ALE method, while the VoS-ψ method leads to inaccuracies that are mostly corrected by the VoS-ψ’ formulation. In addition, the VoS methods are significantly faster than the ALE method, with a speed-up factor of between 2 and 12.
... Experimental studies using a column packed with quartz and magnesite have confirmed the significant role of spatial heterogeneities in subsurface reactive transport and can be used to quantify the effect of spatial mineral distribution on dissolution rates (Salehikhoo et al. 2013;Li et al. 2014;Li and Salehikhoo 2015). X-ray micro-tomography provides observations of the impact of physical and chemical heterogeneity on reaction rates in multimineral porous media (Tutolo et al. 2015;Luhmann et al. 2017;Al-Khulaifi et al. 2017Menke et al. 2016Menke et al. , 2018. Fischer et al. (2014) and Fischer and Luttge (2017) studied how mineral surface roughness at the nanometer scale affects surface reaction rates and proposed to upscale the mineral reaction rate using Monte Carlo simulations. ...
Due to spatial scaling effects, there is a discrepancy in mineral dissolution rates measured at different spatial scales. Many reasons for this spatial scaling effect can be given. We investigate one such reason, i.e., how pore-scale spatial heterogeneity in porous media affects overall mineral dissolution rates. Using the bundle-of-tubes model as an analogy for porous media, we show that the Darcy-scale reaction order increases as the statistical similarity between the pore sizes and the effective-surface-area ratio of the porous sample decreases. The analytical results quantify mineral spatial heterogeneity using the Darcy-scale reaction order and give a mechanistic explanation to the usage of reaction order in Darcy-scale modeling. The relation is used as a constitutive relation of reactive transport at the Darcy scale. We test the constitutive relation by simulating flow-through experiments. The proposed constitutive relation is able to model the solute breakthrough curve of the simulations. Our results imply that we can infer mineral spatial heterogeneity of a porous media using measured solute concentration over time in a flow-through dissolution experiment.
... In these systems, heterogeneities in the porous structure often exist at multiple scales, which can range from micrometers to kilometers in the case of the geological subsurface [4]. The smaller-scale heterogeneities can often have larger-scale macroscopic impacts [5] and understanding the interaction between multiscale heterogeneities is key to predicting large-scale phenomena [6]. However, methodologies to characterize and model multiscale heterogeneous systems in a tractable way are lacking. ...
Field-of-view and resolution trade-offs in x-ray micro-computed-tomography (micro-CT) imaging limit the characterization, analysis, and model development of multiscale porous systems. To this end, we develop an applied methodology utilizing deep learning to enhance low-resolution (LR) images over large sample sizes and create multiscale models capable of accurately simulating experimental fluid dynamics from the pore (microns) to continuum (centimeters) scale. We develop a three-dimensional (3D) enhanced deep-superresolution (EDSR) convolutional neural network to create superresolution (SR) images from LR images, which alleviates common micro-CT hardware and/or reconstruction defects in high-resolution (HR) images. When paired with pore-network simulations and parallel computation, we can create large 3D continuum-scale models with spatially varying flow and material properties. We quantitatively validate the workflow at various scales using direct HR and SR image similarity, pore-scale material and/or flow simulations, and continuum-scale multiphase-flow experiments (drainage-immiscible flow pressures and 3D fluid-volume fractions). The SR images and models are comparable to the HR ground truth and generally accurate to within experimental uncertainty at the continuum scale across a range of flow rates. They are found to be significantly more accurate than their LR counterparts, especially in cases where a wide distribution of pore sizes are encountered. The applied methodology opens up the possibility to image, model, and analyze truly multiscale heterogeneous systems that are otherwise intractable.
... The multiphase mass transport process interacts with the fluid-solid heterogeneous reactions, determining the concentration distribution of the reactive species, which in turn affects the chemical reaction rate. Furthermore, the heterogeneous chemical reactions are always accompanied by pore structure evolution, such as mineral acidification [5], which may further modify the multiphase flow pattern and mass transport phenomenon. These multiphysical processes are fully coupled within the pore structure and have a significant effect on macroscopic scales. ...
Multiphase reactive transport in porous media is an important component of many natural and engineering processes. In the present study, boundary schemes for the continuum species transport-lattice Boltzmann (CST-LB) mass transport model and the multicomponent pseudopotential model are proposed to simulate heterogeneous chemical reactions in a multiphase system. For the CST-LB model, a lattice-interface-tracking scheme for the heterogeneous chemical reaction boundary is provided. Meanwhile, a local-average virtual density boundary scheme for the multicomponent pseudopotential model is formulated based on the work of Li et al. [Li, Yu, and Luo, Phys. Rev. E 100, 053313 (2019)]. With these boundary treatments, a numerical implementation is put forward that couples the multiphase fluid flow, interfacial species transport, heterogeneous chemical reactions, and porous matrix structural evolution. A series of comparison benchmark cases are investigated to evaluate the numerical performance for different pseudopotential wetting boundary treatments, and an application case of multiphase dissolution in porous media is conducted to validate the present models' ability to solve complex problems. By applying the present LB models with reasonable boundary treatments, multiphase reactive transport in various natural or engineering scenarios can be simulated accurately.
