Precipitation In Porous Media Research Articles

Investigation of Different Throat Concepts for Precipitation Processes in Saturated Pore-Network Models

AbstractThe development of reliable mathematical models and numerical discretization methods is important for the understanding of salt precipitation in porous media, which is relevant for environmental problems like soil salinization. Models on the pore scale are necessary to represent local heterogeneities in precipitation and to include the influence of solution-air-solid interfaces. A pore-network model for saturated flow, which includes the precipitation reaction of salt, is presented. It is implemented in the open-source simulator DuMu$$^{\textrm{X}}$$ X . In this paper, we restrict ourselves to one-phase flow as a first step. Since the throat transmissibilities determine the flow behaviour in the pore network, different concepts for the decreasing throat transmissibility due to precipitation are investigated. We consider four concepts for the amount of precipitation in the throats. Three concepts use information from the adjacent pore bodies, and one employs a pore-throat model obtained by averaging the resolved pore-scale model in a thin-tube. They lead to different permeability developments, which are caused by the different distribution of the precipitate between the pore bodies and throats. We additionally apply two different concepts for the calculation of the transmissibility. One obtains the precipitate distribution from analytical assumptions, the other from a geometric minimization principle using a phase-field evolution equation. The two concepts do not show substantial differences for the permeability development as long as simple pore-throat geometries are used. Finally, advantages and disadvantages of the concepts are discussed in the context of the considered physical problem and a reasonable effort for the implementation and computational costs.

Evaluation of underground gas storage capacity in the depleted gas reservoir with water evaporation and salt precipitation

Water evaporation and salt precipitation will occur in gas reservoirs and underground gas storage (UGS) with high-salinity formation water during production and operation. This phenomenon seriously affects the efficient and safe operation and gas storage capacity. This work focuses on quantitatively evaluating the UGS capacity based on depleted gas reservoirs considering water evaporation and salt precipitation. The core flooding experiments are conducted to analyze the influence of water evaporation and salt precipitation on rock properties under different water salinity during multi-cycle injection-production. A numerical model considering water evaporation is established to determine the salt precipitation radius around the gas well. According to the experimental and simulation results, a new analytical model is developed to calculate the underground natural gas storage capacity based on material balance principles. The field case study is presented to show the practical potential of the established model. Both formation porosity and permeability in near-well region may be finally improved by water evaporation and salt precipitation under irreducible water condition. In the presence of movable-water, formation porosity and permeability of the near-well region may be firstly improved and finally reduced due to continuous salt precipitation in porous media. Salt-precipitation radius achieves 28.5 m after ten cycles. The UGS capacity is 101.11 × 108 m3 without considering salt precipitation, 1.11% higher than original geological reserves. The UGS capacity considering both irreducible-water evaporation and salt precipitation is 101.03 × 108 m3. However, when the moveable-water evaporation volume increases to 15Virr, the final UGS capacity is further decreased to 98.55 × 108 m3. The UGS capacity has decreased by 0.82%, 1.64%, and 2.45% compared with irreducible water. The continuous evaporation of movable water and salt deposition will reduce the gas storage capacity and cause damage to the UGS. This work provides an effective method to investigate the quantitative impact of water evaporation and salt precipitation on UGS capacity.

State of the Art on Fe Precipitation in Porous Media: Hydrogeochemical Processes and Evolving Parameters

The mixing of terrestrial groundwater and seawater creates dynamic reaction zones in intertidal areas, where land-derived Fe(II) is oxidized to Fe(III) and then precipitates as Fe hydroxides at the groundwater–seawater interface. These hydrogeochemical processes contribute to the formation of iron bands at the saltwater wedge (SW) and beneath the upper saline plume (USP). This study provides a comprehensive review of physical and geochemical processes at field scale in coastal areas, explores the impact of mineral precipitation on pore structure at pore scale, and synthesizes reactive transport modeling (RTM) approaches for illustrating continuum-scale soil physio-chemical parameters during the evolution of porous media. Upon this review, knowledge gaps and research needs are identified. Additionally, challenges and opportunities are presented. Therefore, we reach the conclusion that the incorporation of observational data into a comprehensive physico-mathematical model becomes imperative for capturing the pore-scale processes in porous media and their influence on groundwater flow and solute transport at large scales. Additionally, a synergistic approach, integrating pore-scale modeling and non-invasive imaging, is equally essential for providing detailed insights into intricate fluid–pore–solid interactions for future studies, as well as facilitating the development of regional engineering-scale models and physio-chemical coupled models with diverse applications in marine science and engineering.

Brine Drying and Salt Precipitation in Porous Media: A Microfluidics Study

AbstractDrying and salt precipitation in porous media impact various engineering disciplines, including carbon geological storage in brine reservoirs, with considerable hydraulic and mechanical effects. However, understanding the underlying mechanisms and controlling factors is limited due to the lack of pore‐scale observation and quantitative analysis. We design radial flow microfluidic chips with varying pore heterogeneity and wettability and quantify the pore‐scale dynamics of brine drying and salt precipitation using time‐lapse images and image processing techniques. The gas injection process determines the distribution of residual (drying) brine and is influenced by pore heterogeneity. Higher concentrations of residual brine are observed near the injection well in more heterogeneous porous media. Capillary backflow replenishes evaporative losses near the well during drying in hydrophilic chips. Brine clusters induced by gas injection connect through brine films and reconnect by capillary backflow. Two types of pore habits of salt precipitation are identified: bulk salt within brine clusters and aggregated salt at the air‐brine interface. Salt precipitation, particularly near the injection well, significantly reduces injectivity, with less impact observed in the porous media with uniform pore structure and hydrophobic surfaces.

Lattice Boltzmann modelling of salt precipitation during brine evaporation

Salt precipitation during brine evaporation in porous media is an important phenomenon in a variety of natural and engineering scenarios. This work establishes a multiphase multicomponent lattice Boltzmann (LB) method with phase change for simulating salt precipitation during brine evaporation. In the proposed LB models, the gas–brine multiphase flow, brine evaporation, salt concentration evolution, salt precipitate nucleation and growth are simultaneously considered. Simulations of the Stefan problem are first conducted to verify the proposed numerical models and determine the diffusion coefficient of brine vapour. Once the lattice Boltzmann models have been validated, salt precipitation during brine evaporation is simulated to investigate the competition mechanisms between salt precipitate nucleation and growth reaction. The results show that the typical salt precipitation patterns in existing experimental observation can be successfully reproduced, including the ring-like and pancake-like patterns. The difference in the salt precipitation patterns is explained by the competition mechanism between precipitate growth and nucleation according to the present study. Furthermore, the salt precipitation during gas injection into a microfluidic chip is investigated. The evolution of salt and brine saturation shows similar patterns to existing experimental results, and the effects of the gas injection rate on salt precipitation performance are clarified. The LB models in the present work can simulate salt precipitation with comprehensive consideration of multiphase brine evaporation, salt species mass transport, precipitate nucleation and growth, which have not been realized in previous studies. The numerical showcases demonstrate the excellent performance of the proposed models for the simulation of salt precipitation in porous media, which promise to guide practical engineering applications like CO2 sequestration.

Machine learning assists in increasing the time resolution of X-ray computed tomography applied to mineral precipitation in porous media

Many subsurface engineering technologies or natural processes cause porous medium properties, such as porosity or permeability, to evolve in time. Studying and understanding such processes on the pore scale is strongly aided by visualizing the details of geometric and morphological changes in the pores. For realistic 3D porous media, X-Ray Computed Tomography (XRCT) is the method of choice for visualization. However, the necessary high spatial resolution requires either access to limited high-energy synchrotron facilities or data acquisition times which are considerably longer (e.g. hours) than the time scales of the processes causing the pore geometry change (e.g. minutes). Thus, so far, conventional benchtop XRCT technologies are often too slow to allow for studying dynamic processes. Interrupting experiments for performing XRCT scans is also in many instances no viable approach. We propose a novel workflow for investigating dynamic precipitation processes in porous media systems in 3D using a conventional XRCT technology. Our workflow is based on limiting the data acquisition time by reducing the number of projections and enhancing the lower-quality reconstructed images using machine-learning algorithms trained on images reconstructed from high-quality initial- and final-stage scans. We apply the proposed workflow to induced carbonate precipitation within a porous-media sample of sintered glass-beads. So we were able to increase the temporal resolution sufficiently to study the temporal evolution of the precipitate accumulation using an available benchtop XRCT device.

Spatiotemporal Distribution of Precipitates and Mineral Phase Transition During Biomineralization Affect Porosity–Permeability Relationships

Enzymatically induced calcium carbonate precipitation is a promising geotechnique with the potential, for example, to seal leakage pathways in the subsurface or to stabilize soils. Precipitation of calcium carbonate in a porous medium reduces the porosity and, consequently, the permeability. With pseudo-2D microfluidic experiments, including pressure monitoring and, for visualization, optical microscopy and X-ray computed tomography, pore-space alterations were reliably related to corresponding hydraulic responses. The study comprises six experiments with two different pore structures, a simple, quasi-1D structure, and a 2D structure. Using a continuous injection strategy with either constant or step-wise reduced flow rates, we identified key mechanisms that significantly influence the relationship between porosity and permeability. In the quasi-1D structure, the location of precipitates is more relevant to the hydraulic response (pressure gradients) than the overall porosity change. In the quasi-2D structure, this is different, because flow can bypass locally clogged regions, thus leading to steadier porosity–permeability relationships. Moreover, in quasi-2D systems, during continuous injection, preferential flow paths can evolve and remain open. Classical porosity–permeability power-law relationships with constant exponents cannot adequately describe this phenomenon. We furthermore observed coexistence and transformation of different polymorphs of calcium carbonate, namely amorphous calcium carbonate, vaterite, and calcite and discuss their influence on the observed development of preferential flow paths. This has so far not been accounted for in the state-of-the-art approaches for porosity–permeability relationships during calcium carbonate precipitation in porous media.

Experimental Study of Evaporation Flux, Salt Precipitation, and Surface Temperature on Homogeneous and Heterogeneous Porous Media

Salt precipitation in porous media is widespread, which has garnered great research attention. However, the mechanisms governing the salt precipitation, water flux, and surface temperature changes in homogeneous and heterogeneous porous media remain unclear. This study investigated the dynamics of salt precipitation, evaporative loss, and surface temperature in homogeneous fine sand (0.1–0.25 mm), coarse sand (1‐2 mm), and a heterogeneous column with fine and coarse sand. All sand columns were initially saturated with NaCl solution. The experimental results showed that the salt was precipitated as efflorescence above the surface of the fine sand, whereas it was mainly precipitated as subflorescence below the surface of the coarse sand, causing the unconsolidated sand to form a strong stone‐like mass. The evaporated loss was significantly higher in heterogeneous than in homogeneous sand, but this difference in evaporation was insignificant in the stage where vapor diffuses through the precipitated salt to the external air. The salt crust formed not only decreased the surface temperature due to increased albedo by salt precipitation, but also resulted in a more discrete temperature distribution in the porous media. Our research results can promote further understanding of salt precipitation and evaporation in porous media.

Combining innovative experimental approaches and cross-scale reactive transport modelling for assessing coupled hydrogeochemical processes at interfaces in deep geological repositories for radioactive waste

Abstract. Deep geological repositories with a multi-barrier concept are foreseen by various countries for the disposal of high-level radioactive waste. A reliable and consistent assessment of the safety of these repositories over time scales of some hundred thousand years requires an advancement of process understanding. Simulation tools need to be developed for a close-to-reality description of repository evolution scenarios. This is especially required to resolve the challenging task of comparing and assessing the safety of different repository concepts in different host rocks within the German site-selection process. The construction of underground galleries and geotechnical barriers in the host rock formation and the emplacement of nuclear waste packages will create perturbations induced by chemical, thermal and pressure gradients at the interfaces of the different barriers, leading to mineral dissolution and precipitation to achieve re-equilibration. Such coupled hydrogeochemical processes generate non-linear responses in transport and mechanical properties of barrier materials and host rocks, which have to be taken into account for a more rigorous assessment of repository system evolution. Reactive transport modeling (RTM) can be applied to investigate these perturbations and processes across temporal and spatial scales, from the micro-scale at interfaces via the repository near field to the entire repository system – information not accessible through experiments alone. Although RTM is capable of addressing highly complex hydrogeochemical phenomena, the application of RTM codes to real systems is impeded by the often simplified description of coupled processes. To enhance the predictive capabilities of reactive transport models and to gain fundamental insights into the coupling between solute and radionuclide transport properties (e.g., permeability and diffusivity) of porous media and dissolution/precipitation processes, we conducted experiments on “simplified” chemical systems combined with pore-scale and continuum-scale reactive transport modelling to study processes in isolation, with the final aim of improving conceptual approaches for process couplings implemented in reactive transport codes. In this context, we investigated the effects of coupled mineral dissolution and precipitation in porous media on changes in permeability using flow-through experiments conducted in a magnetic resonance imaging scanner, which enabled the in situ investigation of porosity evolution in combination with monitoring changes in permeability and mineralogy. Our observations showed that classical implementations in reactive transport codes such as the Kozeny–Carman equation (Carman, 1937) failed to reproduce the changes in permeability and that more sophisticated approaches are required (Poonoosamy et al., 2020a, b). Moreover, we developed a novel “lab-on-a-chip” setup, i.e., micronized counter diffusion reactors with in operando 3D Raman tomography (Poonoosamy et al., 2019, 2020c), which enables evaluation of the alteration in pore architecture and study of the effect of coupled mineral dissolution and precipitation on the diffusive transport of solutes and radionuclides in porous media. Our approach enables the development of process-based theoretical models which allow for improvements in RTM codes and for predicting the evolution of perturbed interfaces in waste repositories, thus building confidence in the predictive capabilities of reactive transport models and reducing uncertainties with respect to future repository evolution.

Barite precipitation in porous media: Impact of pore structure and surface charge on ionic diffusion

Several scientific fields such as global carbon sequestration, deep geological radioactive waste disposal, and oil recovery/fracking encounter safety assessment issues originating from pore-scale processes such as mineral precipitation and dissolution. These processes occur in situations where the pore solution contains chemical complexity (such as pH, ionic strength, redox chemistry, etc.…) and the porous matrix contains physical complexity (such as pore size distribution, surface charge, surface roughness, etc.…). Thus, to comprehend the participation of each physicochemical phenomenon on governing mineral precipitation, it is essential to investigate the precipitation behavior of a given mineral in different confined volumes. In this study, a counter-diffusion approach was used to investigate barite precipitation in two porous materials: micritic chalk and compacted kaolinite. The two materials present similar water and anionic tracer diffusivities and total accessible porosities but distinct pore size distributions with pore throats of c.a. 660 nm in chalk versus c.a. 35 nm in kaolinite.X-ray tomography results obtained on the two materials showed a distinct distribution of barite precipitates: a 500 μm-thick homogeneous layer in chalk versus spherical clusters spread in a thickness of 2 mm in kaolinite. Mass balance calculations showed that barite precipitation led to a porosity decrease in the chalk reacted zone from 45% to 12% and in the kaolinite reacted zone from 36% to 34.5%. In contrast, water tracer diffusion experiments showed that diffusivity decreased by a factor of 28 in chalk and by a factor of 1000 in kaolinite. Such a discrepancy was attributed to the difference in the pore size distribution that would lead to the distinct barite precipitation patterns, capable of altering in a very different manner the connectivity within the reacted zone of the two selected porous media.Such local alterations in connectivity linked to pore volume reduction would also magnify surface charge effects on ionic transport, as indicated by chloride diffusion experiments and electrophoric tests using zeta potential measurements. Indeed, 36Cl− was strongly more hindered than water, when diffused in reacted materials, with a diffusivity decrease by a factor of 450 in chalk and a total restriction of 36Cl− in kaolinite. These experiments clearly provide an insight of how local pore structure properties combined with mineral reactivity could help in predicting the evolution of pore scale clogging and its impact on water and ionic diffusive transport.

A novel approach for modeling permeability decline due to mineral scaling: Coupling geochemistry and deep bed filtration theory

Mixing incompatible brines is one of the leading causes of mineral precipitation in porous media. Deposition of the precipitated minerals in pore spaces leads to the porosity and permeability reduction. This study, in the first step, proposes a novel coupled approach for modeling mineral precipitation and deposition in porous media based on geochemistry and deep bed filtration theory. In the proposed approach, minerals precipitate as suspended particles modeled by PHREEQC geochemical package, and deposition of the precipitated minerals is modeled through the deep bed filtration theory. During the second step, results of the proposed approach are verified using the reported experimental data, which show the proposed approach is applicable and accurate with a high degree of confidence. In the third step, the impact of mineral scaling on deposition pattern and permeability decline is studied with respect to the porosity heterogeneity, the existence of fracture, and heterogeneity in the matching parameters of the model. The results of this study show that the porosity heterogeneity influences not only the deposition pattern of the precipitated minerals but also the amount of permeability decline. This paper demonstrates that deep invasion of the precipitated minerals through the porosity heterogeneity and fracture intensifies the permeability decline. It is also observed that heterogeneities in the modeling parameters (formation damage and filtration coefficients) do not affect the permeability decline of the porous media.

Visual study of TiO2 nanofluid stabilization methods on inhibition of asphaltene precipitation in porous media

In situ recovery involves injection of lixiviant into an ore formation to extract a target metal. Applicability of in situ recovery is confined to deposits where adequate permeability exists. A key challenge is establishing uniform contact between the fluid and the formation in fractured environments, particularly if fractures become blocked by gypsum and other precipitates during leaching, which restricts solution flow. The degree of contact between the lixiviant and the ore is most often the critical rate-limiting factor. Prevention of asphaltene precipitation in reservoir rocks has been shown to resolve such issues in petroleum production. This research explores the potential effect of titanium dioxide (TiO2) nanoparticles in destabilizing asphaltene deposition in porous media in the presence of heptol, with a view to extend the understanding gained in this study to an in situ recovery environment. The effect of TiO2 nanofluid on incremental oil recovery was investigated using three different nanofluid stabilization methods: stabilization by ultrasound; alkaline solution addition to the nanofluid; and the application of ultraviolet radiation. The results show that the ultrasonic system is not suitable for TiO2 nanoparticle stabilization in the fluid. Alkaline addition stabilizes TiO2 nanoparticles but decrease acidic sites on the surface of the nanoparticles, which leads to lower asphaltene adsorption on TiO2 nanoparticles and a lower nanoparticle surface charge, and results in nanoparticle flocculation and instability. Ultraviolet radiation was found to be the best method for stabilizing TiO2 nanoparticles. Asphaltene adsorption did not occur at concentrations below 3000 ppm TiO2 and thus, the recovery increase using these concentrations was attributed to an increased viscosity of the injected fluid and a reduction of its interfacial tension with the host oil.

Micro-continuum approach for mineral precipitation

Rates and extents of mineral precipitation in porous media are difficult to predict, in part because laboratory experiments are problematic. It is similarly challenging to implement numerical methods that model this process due to the need to dynamically evolve the interface of solid material. We developed a multiphase solver that implements a micro-continuum simulation approach based on the Darcy–Brinkman–Stokes equation to study mineral precipitation. We used the volume-of-fluid technique in sharp interface implementation to capture the propagation of the solid mineral surface. Additionally, we utilize an adaptive mesh refinement method to improve the resolution of near interface simulation domain dynamically. The developed solver was validated against both analytical solution and Arbitrary Lagrangian–Eulerian approach to ensure its accuracy on simulating the propagation of the solid interface. The precipitation of barite (BaSO4) was chosen as a model system to test the solver using variety of simulation parameters: different geometrical constraints, flow conditions, reaction rate and ion diffusion. The growth of a single barite crystal was simulated to demonstrate the solver’s capability to capture the crystal face specific directional growth.

Modeling of Evaporation-Driven Multiple Salt Precipitation in Porous Media with a Real Field Application

Soil and groundwater salinization are very important environmental issues of global concern. They threaten mainly the arid and semiarid regions characterized by dry climate conditions and an increase of irrigation practices. Among these regions, the south of Tunisia is considered, on the one hand, to be a salt-affected zone facing a twofold problem: The scarcity of water resources and the degradation of their quality due to the overexploitation of the aquifers for irrigation needs. On the other hand, this Tunisian landform is the only adequate area for planting date palm trees which provide the country with the first and most important exportation product. In order to maintain the existence of these oases and develop the date production, a good understanding of the salinization problem threatening this region, and the ability to predict its distribution and evolution, should not be underestimated. The work presented in this paper deals with the Oasis of Segdoud in southern Tunisia, with the objective of modeling the evaporation-driven salt precipitation processes at the soil profile scale and under real climatic conditions. The model used is based on the one developed and presented in a previous work. In order to fulfil the real field conditions, a further extension of the geochemical system of the existing model was required. The precipitated salts considered in this work were halite (NaCl), gypsum (CaSO4) and thenardite (Na2SO4). The extended model reproduces very well the same tendencies of the physico-chemical processes of the natural system in terms of the spatio-temporal distribution and evolution of the evaporation and multiple-salt precipitation. It sheds new lights on the simulation of sequences of salt precipitation in arid regions. The simulation results provide an analysis of the influence of salt precipitation on hydrodynamic properties of the porous medium (porosity and permeability). Moreover, the sensitivity analysis done here reveals the influence of the water table level on the evaporation rate.

Study of Asphaltene Precipitation during CO2 Injection into Oil Reservoirs in the Presence of Iron Oxide Nanoparticles by Interfacial Tension and Bond Number Measurements

CO2 injection is one of the most frequently used enhanced oil recovery methods; however, it causes asphaltene precipitation in porous media and wellbore and wellhead facilities. Carbon dioxide saturated with nanoparticles can be used to enhance oil recovery with lower asphaltene precipitation issues. In this study, the vanishing interfacial tension technique was used to investigate the possibility of diminishing asphaltene precipitation by nanoparticles. The interfacial tension (IFT) of synthetic oil/carbon dioxide was measured using the pendant drop method. The results illustrated that, for synthetic oil samples containing asphaltene, the IFT data versus pressure decrease linearly with two different slopes at low- and high-pressure ranges. At high pressures, the slope of the plot is lower than the one in the low-pressure range. The addition of iron oxide nanoparticles to the oil solution reduces the interfacial tension at higher pressures with a steeper slope, showing that nanoparticles can decrease asphaltene precipitation. The plot of Bond number versus pressure also confirmed the impact of nanoparticles on reducing asphaltene precipitation. In terms of the temperature effect, the presence of nanoparticles at 50 °C resulted in a 16.34% reduction in asphaltene precipitation and a 19.65% reduction at 70 °C. The minimum miscibility pressure changed from 10.17 to 30.96 MPa at 70 °C; however, in the presence of nanoparticles, it reduced from 10.06 to 16.56. Therefore, the technique introduced in this study could be applied to avoid the problems associated with altering the gas injection mode from miscible to immiscible.

Effects of solution supersaturation on barite precipitation in porous media and consequences on permeability: Experiments and modelling

The understanding of porosity evolution in porous media due to mineral reactions and its impact on the transport of fluids and solutes is important, as this is a key factor in the long-term behaviour of underground engineered systems. The implementation of such coupled processes into numerical codes requires a mechanistic understanding of the relevant precipitation/dissolution processes in porous media and model validation with quantitative experiments. In this context, we conducted a series of flow-through column experiments to investigate the effect of supersaturation on barite precipitation mechanisms (e.g. nucleation) and consequential permeability changes. These experiments were modelled using the reactive transport code OpenGeoSys-GEM. Although the Kozeny-Carman equation is widely applied in numerical models describing porosity and permeability changes due to mineral dissolution and precipitation, it distinctively underestimated the permeability changes observed in the experiments. Instead, a porosity-permeability relationship involving a critical porosity at which the permeability decreases significantly had to be considered in the model. Post-mortem characterization (Scanning Electron Microscopy) highlighted the importance of including pore-scale information on passivation processes in order to get a better match between experimental and simulated results.

Supercritical CO2-EOR in an asphaltenic tight sandstone formation and the changes of rock petrophysical properties induced by asphaltene precipitation

This work targeted an asphaltenic tight formation and thoroughly investigated the effectiveness of supercritical CO2 (scCO2) injection in enhancing oil recovery. Particular attention was placed on the changes of rock petrophysical properties induced by asphaltene precipitation in porous media. Low-field Nuclear magnetic resonance (LF-NMR) spectrometer and SEM-EDS were employed to characterize the changes. The results indicated that high injection pressure was favorable for enhanced oil recovery (EOR) but accelerated asphaltene precipitation in formation. The precipitated asphaltenes notably reduced rock permeability and porosity, in which the large pores were more likely to be damaged. The wettability of rock surface was hardly altered with an exception of the inlet face. The results of this study supplement earlier observations and can provide insights into tight reservoirs EOR especially in the presence of asphaltenes.

X‐Ray Computed Microtomography Imaging of Abiotic Carbonate Precipitation in Porous Media From a Supersaturated Solution: Insights Into Effect of CO2 Mineral Trapping on Permeability

AbstractAbiotic carbonate precipitation has garnered significant interest as a mechanism for mineral trapping of carbon dioxide (CO2) in geologic carbon storage, as a natural diagenetic process frequently occurring in marine environments, and as an engineering approach for soil improvement. This study explored pore‐scale precipitation of calcium carbonate (CaCO3) and its effect on the permeability of porous media, using X‐ray computed microtomography (CMT). In a column experiment, CaCO3 was precipitated in a sand pack from a supersaturated CaCO3 solution, while porosity, pore volume fraction of carbonate, and permeability were being monitored and X‐ray CMT images were being acquired. Permeability reduction by ~99.94% was observed when precipitated carbonate occupied ~46–47% of pore volume. The X‐ray CMT images showed that carbonate crystals were initially nucleated onto sand grain surfaces, which facilitated subsequent precipitation, indicating a predominantly grain‐coating behavior. The scanning electron microscopy revealed the carbonate crystals of ~1–20 μm in size and the presence of internal pores in the carbonate layers at the submicrometer scale. Variations in carbonate layer thickness and geometric tortuosity, and preferential carbonate precipitation behavior with local clogging were examined through morphological analysis and phase segmentation. Particularly, the pore‐scale precipitation pattern and hence the pore geometry were found to evolve with continued precipitation from a grain‐coating behavior, through a pore‐filling behavior, and finally into a dramatic pore‐throat‐clogging behavior. Our results provide unique experiment data for predictive modeling of long‐term CO2 transport and provide new insights into the changes in physical and transport properties during CO2 mineral trapping.

Time-fractional characterization of brine reaction and precipitation in porous media.

Brine reaction and precipitation in porous media sometimes occur in the presence of a strong fluid flowing field, which induces the mobilization of the precipitated salts and distorts their spatial distribution. It is interesting to investigate how the distribution responds to such mobilization. We view these precipitates as random walkers in the complex inner space of the porous media, where they make stochastic jumps among locations and possibly wait between successive transitions. In consideration of related experimental results, the waiting time of the precipitates at a particular position is allowed to range widely from short sojourn to permanent residence. Through the model of a continuous-time random walk, a class of time-fractional equations for the precipitate's concentration profile is derived, including that in the Riemann-Liouville formalism and the Prabhakar formalism. The solutions to these equations show the general pattern of the precipitate's spatiotemporal evolution: a coupling of mass accumulation and mass transport. And the degree to which the mass is mobilized turns out to be monotonically correlated to the fractional exponent α. Moreover, to keep the completeness of the model, we further discuss how the interaction among the precipitates influences the precipitation process. In doing so, a time-fractional non-linear Fokker-Planck equation with source term is introduced and solved. It is shown that the interaction among the precipitates slightly perturbs their spatial distribution. This distribution is largely dominated by the brine reaction itself and the interaction between the precipitates and the porous media.

Pore-network model of evaporation-induced salt precipitation in porous media: The effect of correlations and heterogeneity

Abstract Salt transport and precipitation in porous media constitute a set of complex and fascinating phenomena that are of considerable interest to several important problems, ranging from storage of CO2 in geological formations, to soil fertility, and protection of pavements and roads, as well as historical monuments. The phenomena occur at the pore scale and are greatly influenced by the heterogeneity of the pore space morphology. We present a pore-network (PN) model to study the phenomena. Vapor diffusion, capillary effect at the brine-vapor interface, flow of brine, and transport of salt and its precipitation in the pores that plug the pores partially or completely are all accounted for. The drying process is modeled by the invasion percolation, while transport of salt in brine is accounted for by the convective-diffusion equation. We demonstrate that the drying patterns, the clustering and connectivity of the pore throats in which salt precipitation occurs, the saturation distribution, and the drying rate are all strongly dependent upon the pore-size distribution, the correlations among the pore sizes, and the anisotropy of the pore space caused by stratification that most natural porous media contain. In particular, if the strata are more or less parallel to the direction of injection of the gas that dries out the pore space (air, for example) and/or causes salt precipitation (CO2, for example), the drying rate increases significantly. Moreover, salt tends to precipitate in clusters of neighboring pores that are parallel to the open surface of the porous medium.