The Experts below are selected from a list of 5916 Experts worldwide ranked by ideXlab platform
Josep M Soler - One of the best experts on this subject based on the ideXlab platform.
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interaction between co2 rich acidic water hydrated portland cement and sedimentary rocks column experiments and Reactive Transport Modeling
Chemical Geology, 2021Co-Authors: Gabriela Davila, Jordi Cama, Carme M Chaparro, Barbara Lothenbach, Douglas R Schmitt, Josep M SolerAbstract:Abstract Percolation experiments, using columns filled with alternating layers of hydrated Portland cement and crushed sedimentary rocks, were conducted at PCO2 = 10 bar and 60 °C. Limestone, sandstone and marl were representative of reservoir and cap rocks for a geologic CO2 storage site. The injected solution was at equilibrium with gypsum and equilibrated with the CO2. The main reactions were the dissolution of the calcite that constitutes the rocks and the hydrotalcite and portlandite of the Portland cement. The resulting porewaters were supersaturated with respect to aragonite and gypsum, leading to their precipitation. 2D Reactive Transport simulations successfully reproduced the experimental aqueous chemistry changes caused by the major dissolution of calcite, portlandite and hydrotalcite together with the precipitation of aragonite, dolomite (cement carbonation), gypsum and alunite. Porosity increased to different extents in both cement and rock. Cement degradation was noticeable in all the cases, but even more in the sandstone experiment.
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interaction between co2 rich acidic water hydrated portland cement and sedimentary rocks column experiments and Reactive Transport Modeling
Chemical Geology, 2021Co-Authors: Gabriela Davila, Jordi Cama, Carme M Chaparro, Barbara Lothenbach, Douglas R Schmitt, Josep M SolerAbstract:Abstract Percolation experiments, using columns filled with alternating layers of hydrated Portland cement and crushed sedimentary rocks, were conducted at PCO2 = 10 bar and 60 °C. Limestone, sandstone and marl were representative of reservoir and cap rocks for geologic CO2 storage. The injected solution was at equilibrium with gypsum and equilibrated with the CO2. The main reactions were the dissolution of the calcite making up the rocks and the hydrotalcite and portlandite of the Portland cement. The resulting porewaters were supersaturated with respect to aragonite and gypsum, leading to their precipitation. 2D Reactive Transport simulations successfully reproduced the experimental aqueous chemistry changes caused by the major dissolution of calcite, portlandite and hydrotalcite together with the precipitation of aragonite, dolomite (cement carbonation), gypsum and alunite. Porosity increased to different extents in both cement and rock. Cement degradation was important in all the cases, but even more in the sandstone experiment.
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reactivity of a marl caprock in contact with acid solutions under different pco2 conditions atmospheric 10 and 37 bar
Procedia Earth and Planetary Science, 2017Co-Authors: Gabriela Davila, Jordi Cama, Linda Luquot, Josep M Soler, Carlos AyoraAbstract:Abstract Laboratory column experiments using crushed marly limestone, bituminous black shale and marl were conducted under different P Total - p CO 2 (atmospheric: 1-10 -3.5 , subcritical: 10-10 bar and supercritical: 150-37 bar) and T (25 and 60 °C) conditions and using different input solutions (gypsum-undersaturated and gypsum-equilibrated). 1D Reactive Transport Modeling was performed to quantify the overall process of gypsum precipitation at the expense of calcite dissolution in CO 2 -rich solutions together with minor dissolution of albite and clinochlore.
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2d Reactive Transport Modeling of the interaction between a marl and a co2 rich sulfate solution under supercritical co2 conditions
International Journal of Greenhouse Gas Control, 2016Co-Authors: Linda Luquot, Gabriela Davila, Josep M Soler, Jordi CamaAbstract:Abstract The circulation of CO2-rich solutions through fractured marl cores (caprock) under different flow rates and supercritical CO2 conditions (PTotal = 150 bar, pCO2 = 61 bar and T = 60 °C) led to mineral changes caused mainly by calcite dissolution and to a lesser extent by aluminosilicate dissolution, and by gypsum precipitation adjacent to the fracture walls. Another significant result was the formation of the altered and highly porous zone ( Davila et al., 2016a ). Dissolution structures ranged from face to uniform dissolution and wormhole formation depending mainly on the flow rate. 2D Reactive Transport models were used to interpret the results of the percolation experiments (except at 60 mL h−1). They reproduced the variation in the outflow composition with time and the observed width of the altered zone along the fractures. A good match was achieved by using initial Deff values in the rock matrix that ranged from 1 × 10−13 m2 s−1 to 3 × 10−13 m2 s−1 under slow flow rates. The Deff value was higher by a factor of 20 (6 × 10−12 m2 s−1) under fast flow. Moreover, a slight variation in the calcite Reactive surface areas contributed to the fit of the model to the experimental data. The Modeling results reproduced major dissolution of calcite and gypsum precipitation, and minor dissolution of clinochlore. Calcite dissolution was boosted by increasing the flow rate and gypsum precipitation increased at intermediate flow rate (1 mL h−1). Minor precipitation of dolomite, kaolinite, boehmite and three zeolites (mesolite, stilbite and smectite) along the altered zone occurred. The magnitude of these reactions was consistent with the measured increase in porosity over the altered zone.
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Reactive Transport Modeling of the interaction between a high ph plume and a fractured marl the case of wellenberg
Applied Geochemistry, 2003Co-Authors: Josep M SolerAbstract:Abstract In the context of the proposed low- and intermediate-level radioactive waste repository at Wellenberg (Switzerland), calculations simulating the interaction between hyperalkaline solutions and a fractured marl, at 25 °C, have been performed. The aim of these calculations is to evaluate the possible effects of mineral dissolution and precipitation on porosity and permeability changes in such a fractured marl, and their impact on repository performance. Solute Transport and chemical reaction are considered in both a high-permeability zone (fracture), where advection is important, and the wall rock, where diffusion is the dominant Transport mechanism. The mineral reactions are promoted by the interaction between hyperalkaline solutions derived from the degradation of cement (a major component of the engineered barrier system in the repository) and the host rock. Both diffusive/dispersive and advective solute Transport are taken into account in the calculations. Mineral reactions are described by kinetic rate laws. The fluid flow system under consideration is a two-dimensional porous medium (marl, 1% porosity), with a high-permeability zone simulating a fracture (10% porosity) crossing the domain. The dimensions of the domain are 6 m per 1 m, and the fracture width is 10 cm. The fluid flow field is updated during the course of the simulations. Permeabilities are updated according to Kozeny's equation. The composition of the solutions entering the domain is derived from Modeling studies of the degradation of cement under the conditions at the proposed underground repository at Wellenberg. Two different cases have been considered in the calculations. These 2 cases are representative of 2 different stages in the process of degradation of cement (pH 13.5 and pH 12.5). In both cases, the flow velocity in the fracture diminishes with time, due to a decrease in porosity. This decrease in porosity is caused by the precipitation of calcite (replacement of dolomite by calcite) and other secondary minerals (brucite, sepiolite, analcime, natrolite, tobermorite). However, the decrease in porosity and flow velocity is much more pronounced in the lower pH case. The extent of the zone of mineral alteration along the fracture is also much more limited in the lower pH case. The reduction of porosity in the fractures would be highly beneficial for repository performance, since it would mean that the solutions coming from the repository and potentially carrying radionuclides in solution would have to flow through low-conductive rock before they would be able to get to higher-conductive features. The biggest uncertainty in the reaction rates used in the calculations arises from the surface areas of the primary minerals. Additional calculations making use of smaller surface areas have also been performed. The results show that the smaller surface areas (and therefore smaller reaction rates) result in a smaller reactivity of the system and smaller porosity changes.
David W. Blowes - One of the best experts on this subject based on the ideXlab platform.
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Reactive Transport Modeling of trichloroethene treatment with declining reactivity of iron
Environmental Science & Technology, 2007Co-Authors: Sungwook Jeen, Ulrich K Mayer, Robert W Gillham, David W. BlowesAbstract:Evolving reactivity of iron, resulting from precipitation of secondary minerals within iron permeable Reactive barriers (PRBs), was included in a Reactive Transport model for trichloroethene (TCE) treatment. The accumulation of secondary minerals and reactivity loss were coupled using an empirically derived relationship that was incorporated into an existing multicomponent Reactive Transport code (MIN3P) by modifying the kinetic expressions. The simulation results were compared to the observations from long-term column experiments, which were designed to assess the effects of carbonate mineral formation on the performance of iron for TCE treatment. The model successfully reproduced the evolution of iron reactivity and the dynamic changes in geochemical conditions and contaminant treatment. Predictions under various hydrogeochemical conditions showed that TCE would be treated effectively for an extended period of time without a significant loss of permeability. Although there are improvements yet to be made, this study provides a significant advance in our ability to predict long-term performance of iron PRBs.
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process based Reactive Transport Modeling of a permeable Reactive barrier for the treatment of mine drainage
Journal of Contaminant Hydrology, 2006Co-Authors: K U Mayer, Shawn G Benner, David W. BlowesAbstract:Abstract Reactive Transport Modeling of a permeable Reactive barrier for the treatment of mine drainage was used to integrate a comprehensive data set including pore water chemistry and solid phase data from several sampling events over a >3-year time period. The simulations consider the reduction of sulfate by the organic carbon-based treatment material and the removal of sulfate and iron by precipitation of reduced mineral phases including iron monosulfides and siderite. Additional parameters constraining the model include dissolved H 2 S, alkalinity and pH, as well as a suite of solid phase S-fractions identified by extractions. Influences of spatial heterogeneity necessitated the use of a 2-dimensional Modeling approach. Simulating observed seasonal fluctuations and long-term changes in barrier reactivity required the use of temperature dependent rate coefficients and a multimodal Monod-type rate expression accounting for the variable reactivity of different organic carbon fractions. Simulated dissolved concentrations of SO 4 , Fe, H 2 S, alkalinity and pH, as well as solid phase accumulations of reduced sulfur phases generally compare well to observed trends over 23 months. Spatial variations, seasonal fluctuations and the time-dependent decline in reactivity were also captured. The Modeling results generally confirm, and further strengthen, the existing conceptual model for the site. Overall sulfate reduction and S-accumulation rates are constrained with confidence within a factor of 1.5.
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Multicomponent Reactive Transport Modeling of acid neutralization reactions in mine tailings
Water Resources Research, 2004Co-Authors: Jasna Jurjovec, David W. Blowes, Carol J. Ptacek, K. Ulrich MayerAbstract:[1] Multicomponent Reactive Transport Modeling was conducted to analyze and quantify the acid neutralization reactions observed in a column experiment. Experimental results and the experimental procedures have been previously published. The pore water geochemistry was described by dissolution and precipitation reactions involving primary and secondary mineral phases. The initial amounts of the primary phases ankerite-dolomite, siderite, chlorite, and gypsum were constrained by mineralogical analyses of the tailings sample used in the experiment. Secondary gibbsite was incorporated into the model to adequately explain the changes in pH and concentration changes of Al in the column effluent water. The results of the Reactive Transport Modeling show that the pH of the column effluent water can be explained by dissolution reactions of ankerite-dolomite, siderite, chlorite, and secondary gibbsite. The Modeling results also show that changes in Eh can be explained by dissolution of ferrihydrite during the experiment. In addition, the Modeling results show that the kinetically limited dissolution of chlorite contributes the largest mass of dissolved Mg and Fe (II) in the effluent water, followed by ankerite-dolomite, which contributes substantially less. In summary, Reactive Transport Modeling based on detailed geochemical and mineralogical data was successful to quantitatively describe the changes in pH and major ions in the column effluent.
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Multicomponent Reactive Transport Modeling in variably saturated porous media using a generalized formulation for kinetically controlled reactions
Water Resources Research, 2002Co-Authors: K. Ulrich Mayer, Emil O. Frind, David W. BlowesAbstract:1 A generalized formulation for kinetically controlled reactions has been developed and incorporated into a multicomponent Reactive Transport model to facilitate the investigation of a large variety of problems involving inorganic and organic chemicals in variably saturated media. The general kinetic formulation includes intra-aqueous and dissolution-precipitation reactions in addition to geochemical equilibrium expressions for hydrolysis, aqueous complexation, oxidation-reduction, ion exchange, surface complexation, and gas dissolution-exsolution reactions. The generalized approach allows consideration of fractional order terms with respect to any dissolved species in terms of species activities or in terms of total concentrations, which facilitates the incorporation of a variety of experimentally derived rate expressions. Monod and inhibition terms can be used to describe microbially mediated reactions or to limit the reaction progress of inorganic reactions. Dissolution-precipitation reactions can be described as surface-controlled or Transport-controlled reactions. The formulation also facilitates the consideration of any number of parallel reaction pathways, and reactions can be treated as irreversible or reversible processes. Two groundwater contamination scenarios, both set in variably saturated media but with significantly different geochemical reaction networks, are investigated and demonstrate the advantage of the generalized approach. The first problem focuses on a hypothetical case study of the natural attenuation of organic contaminants undergoing dissolution, volatilization, and biodegradation in an unconfined aquifer overlaid by unsaturated sediments. The second problem addresses the generation of acid mine drainage in the unsaturated zone of a tailings impoundment at the Nickel Rim Mine Site near Sudbury, Ontario, and subsequent Reactive Transport in the saturated portion of the tailings.
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Reactive Transport Modeling of an in situ Reactive barrier for the treatment of hexavalent chromium and trichloroethylene in groundwater
Water Resources Research, 2001Co-Authors: Ulrich K Mayer, David W. Blowes, Emil O. FrindAbstract:Multicomponent Reactive Transport Modeling was conducted for the permeable Reactive barrier at the Coast Guard Support Center near Elizabeth City, North Carolina. The zero-valent iron barrier was installed to treat groundwater contaminated by hexavalent chromium and chlorinated solvents. The simulations were performed using the Reactive Transport model MIN3P, applied to an existing site-specific conceptual model. Reaction processes controlling the geochemical evolution within and down gradient of the barrier were considered. Within the barrier, the treatment of the contaminants, the reduction of other electron acceptors present in the ambient groundwater, microbially mediated sulfate reduction, the precipitation of secondary minerals, and degassing of hydrogen gas were included. Down gradient of the barrier, water-rock interactions between the highly alkaline and reducing pore water emanating from the barrier and the aquifer material were considered. The model results illustrate removal of Cr(VI) and the chlorinated solvents by the Reactive barrier and highlight that reactions other than the remediation reactions most significantly affect the water chemistry in the barrier. In particular, sulfate reduction and iron corrosion by water control the evolution of the pore water while passing through the treatment system. The simulation results indicate that secondary mineral formation has the potential to decrease the porosity in the barrier over the long term and illustrate that the precipitation of minerals is concentrated in the upgradient portion of the barrier. Two-dimensional simulations demonstrate how preferential flow can affect the reduction of electron acceptors, the consumption of the treatment material, and the formation of secondary minerals. In addition, the model results indicate that deprotonation and the adsorption of cations down gradient of the barrier can potentially explain the observed pH buffering.
Gabriela Davila - One of the best experts on this subject based on the ideXlab platform.
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interaction between co2 rich acidic water hydrated portland cement and sedimentary rocks column experiments and Reactive Transport Modeling
Chemical Geology, 2021Co-Authors: Gabriela Davila, Jordi Cama, Carme M Chaparro, Barbara Lothenbach, Douglas R Schmitt, Josep M SolerAbstract:Abstract Percolation experiments, using columns filled with alternating layers of hydrated Portland cement and crushed sedimentary rocks, were conducted at PCO2 = 10 bar and 60 °C. Limestone, sandstone and marl were representative of reservoir and cap rocks for a geologic CO2 storage site. The injected solution was at equilibrium with gypsum and equilibrated with the CO2. The main reactions were the dissolution of the calcite that constitutes the rocks and the hydrotalcite and portlandite of the Portland cement. The resulting porewaters were supersaturated with respect to aragonite and gypsum, leading to their precipitation. 2D Reactive Transport simulations successfully reproduced the experimental aqueous chemistry changes caused by the major dissolution of calcite, portlandite and hydrotalcite together with the precipitation of aragonite, dolomite (cement carbonation), gypsum and alunite. Porosity increased to different extents in both cement and rock. Cement degradation was noticeable in all the cases, but even more in the sandstone experiment.
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interaction between co2 rich acidic water hydrated portland cement and sedimentary rocks column experiments and Reactive Transport Modeling
Chemical Geology, 2021Co-Authors: Gabriela Davila, Jordi Cama, Carme M Chaparro, Barbara Lothenbach, Douglas R Schmitt, Josep M SolerAbstract:Abstract Percolation experiments, using columns filled with alternating layers of hydrated Portland cement and crushed sedimentary rocks, were conducted at PCO2 = 10 bar and 60 °C. Limestone, sandstone and marl were representative of reservoir and cap rocks for geologic CO2 storage. The injected solution was at equilibrium with gypsum and equilibrated with the CO2. The main reactions were the dissolution of the calcite making up the rocks and the hydrotalcite and portlandite of the Portland cement. The resulting porewaters were supersaturated with respect to aragonite and gypsum, leading to their precipitation. 2D Reactive Transport simulations successfully reproduced the experimental aqueous chemistry changes caused by the major dissolution of calcite, portlandite and hydrotalcite together with the precipitation of aragonite, dolomite (cement carbonation), gypsum and alunite. Porosity increased to different extents in both cement and rock. Cement degradation was important in all the cases, but even more in the sandstone experiment.
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reactivity of a marl caprock in contact with acid solutions under different pco2 conditions atmospheric 10 and 37 bar
Procedia Earth and Planetary Science, 2017Co-Authors: Gabriela Davila, Jordi Cama, Linda Luquot, Josep M Soler, Carlos AyoraAbstract:Abstract Laboratory column experiments using crushed marly limestone, bituminous black shale and marl were conducted under different P Total - p CO 2 (atmospheric: 1-10 -3.5 , subcritical: 10-10 bar and supercritical: 150-37 bar) and T (25 and 60 °C) conditions and using different input solutions (gypsum-undersaturated and gypsum-equilibrated). 1D Reactive Transport Modeling was performed to quantify the overall process of gypsum precipitation at the expense of calcite dissolution in CO 2 -rich solutions together with minor dissolution of albite and clinochlore.
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2d Reactive Transport Modeling of the interaction between a marl and a co2 rich sulfate solution under supercritical co2 conditions
International Journal of Greenhouse Gas Control, 2016Co-Authors: Linda Luquot, Gabriela Davila, Josep M Soler, Jordi CamaAbstract:Abstract The circulation of CO2-rich solutions through fractured marl cores (caprock) under different flow rates and supercritical CO2 conditions (PTotal = 150 bar, pCO2 = 61 bar and T = 60 °C) led to mineral changes caused mainly by calcite dissolution and to a lesser extent by aluminosilicate dissolution, and by gypsum precipitation adjacent to the fracture walls. Another significant result was the formation of the altered and highly porous zone ( Davila et al., 2016a ). Dissolution structures ranged from face to uniform dissolution and wormhole formation depending mainly on the flow rate. 2D Reactive Transport models were used to interpret the results of the percolation experiments (except at 60 mL h−1). They reproduced the variation in the outflow composition with time and the observed width of the altered zone along the fractures. A good match was achieved by using initial Deff values in the rock matrix that ranged from 1 × 10−13 m2 s−1 to 3 × 10−13 m2 s−1 under slow flow rates. The Deff value was higher by a factor of 20 (6 × 10−12 m2 s−1) under fast flow. Moreover, a slight variation in the calcite Reactive surface areas contributed to the fit of the model to the experimental data. The Modeling results reproduced major dissolution of calcite and gypsum precipitation, and minor dissolution of clinochlore. Calcite dissolution was boosted by increasing the flow rate and gypsum precipitation increased at intermediate flow rate (1 mL h−1). Minor precipitation of dolomite, kaolinite, boehmite and three zeolites (mesolite, stilbite and smectite) along the altered zone occurred. The magnitude of these reactions was consistent with the measured increase in porosity over the altered zone.
Karsten Pruess - One of the best experts on this subject based on the ideXlab platform.
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the effects of gas fluid rock interactions on co2 injection and storage insights from Reactive Transport Modeling
Energy Procedia, 2009Co-Authors: Yitian Xiao, Tianfu Xu, Karsten PruessAbstract:Abstract Possible means of reducing atmospheric CO 2 emissions include injecting CO 2 in petroleum reservoirs for Enhanced Oil Recovery or storing CO 2 in deep saline aquifers. Large-scale injection of CO 2 into subsurface reservoirs would induce a complex interplay of multiphase flow, capillary trapping, dissolution, diffusion, convection, and chemical reactions that may have significant impacts on both short-term injection performance and long-term fate of CO 2 storage. Reactive Transport Modeling is a promising approach that can be used to predict the spatial and temporal evolution of injected CO 2 and associated gas-fluid-rock interactions. This presentation will summarize recent advances in Reactive Transport Modeling of CO 2 storage and review key technical issues on (1) the short- and long-term behavior of injected CO 2 in geological formations; (2) the role of reservoir mineral heterogeneity on injection performance and storage security; (3) the effect of gas mixtures (e.g., H 2 S and SO 2 ) on CO 2 storage; and (4) the physical and chemical processes during potential leakage of CO 2 from the primary storage reservoir. Simulation results suggest that CO 2 trapping capacity, rate, and impact on reservoir rocks depend on primary mineral composition and injecting gas mixtures. For example, models predict that the injection of CO 2 alone or co-injection with H 2 S in both sandstone and carbonate reservoirs lead to acidified zones and mineral dissolution adjacent to the injection well, and carbonate precipitation and mineral trapping away from the well. Co-injection of CO 2 with H 2 S and in particular with SO 2 causes greater formation alteration and complex sulfur mineral (alunite, anhydrite, and pyrite) trapping, sometimes at a much faster rate than previously thought. The results from Reactive Transport Modeling provide valuable insights for analyzing and assessing the dynamic behaviors of injected CO 2 , identifying and characterizing potential storage sites, and managing injection performance and reducing costs.
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comparing frachem and toughreact for Reactive Transport Modeling of brine rock interactions in enhanced geothermal systems egs
Lawrence Berkeley National Laboratory, 2008Co-Authors: Laurent Andre, Karsten Pruess, N Spycher, Francoisd VuatazAbstract:Coupled modelling of fluid flow and Reactive Transport in geothermal systems is challenging because of reservoir conditions such as high temperatures, elevated pressures and sometimes high salinities of the formation fluids. Thermal hydrological-chemical (THC) codes, such as FRACHEM and TOUGHREACT, have been developed to evaluate the long-term hydrothermal and chemical evolution of exploited reservoirs. In this study, the two codes were applied to model the same geothermal reservoir, to forecast reservoir evolution using respective thermodynamic and kinetic input data. A recent (unreleased) TOUGHREACT version allows the use of either an extended Debye-Hu?ckel or Pitzer activity model for calculating activity coefficients, while FRACHEM was designed to use the Pitzer formalism. Comparison of models results indicate that differences in thermodynamic equilibrium constants, activity coefficients and kinetics models can result in significant differences in predicted mineral precipitation behaviour and reservoir-porosity evolution. Differences in the calculation schemes typically produce less difference in model outputs than differences in input thermodynamic and kinetic data, with model results being particularly sensitive to differences in ion-interaction parameters for highsalinity systems.
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Two-Dimensional Reactive Transport Modeling of CO2 injection in a saline aquifer at the Sleipner site, North sea
American journal of science, 2007Co-Authors: Pascal Audigane, Irina Gaus, Isabelle Czernichowski-lauriol, Karsten PruessAbstract:This paper presents a 2D Reactive Transport model of long-term geological storage of carbon dioxide. A data set from the Utsira formation in Sleipner (North Sea) is utilized for geochemical simulation, while the aquifer is approximated as a 2D cylindrically symmetric system. Using the Reactive Transport code TOUGHREACT, a 25 year injection scenario followed by a 10,000 year storage period are simulated. Supercritical CO2 migration, dissolution of the CO2 in the brine, and geochemical reactions with the host rock are considered in the model. Two mineralogical assemblages are considered in the Utsira formation, a sand formation that is highly permeable and a shale formation representing four semi-permeable layers in the system that reduce the upward migration of the supercritical CO2. The impacts of mineral dissolution and precipitation on porosity are calculated. Furthermore, the 2D cylindrical geometry of the mesh allows simulating both the upward migration of the supercritical gas bubble as well as the downward migration of the brine containing dissolved CO2. A mass balance of the CO2 stored in, respectively, the supercritical phase, dissolved in the aqueous phase, and sequestered in solid mineral phases (carbonate precipitation) is calculated over time. Simulations with lower residual gas saturation and with different mesh refinement are also performed to test the sensitivity on mass balance estimates.
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Reactive Transport Modeling of injection well scaling and acidizing at tiwi field philippines
Geothermics, 2004Co-Authors: Yvette Ontoy, Nicolas Spycher, Phil Molling, Mauro Parini, Karsten PruessAbstract:Abstract Hot brine injector Nag-67 in the Tiwi geothermal field (Philippines) had been in operation for over 10 years when injectivity decline indicated a workover was required in 2000. The operation consisted of drilling-out wellbore scale followed by acid dissolution of scale formed in the near-wellbore formation. The workover increased the injection capacity of the well to near its initial-use capacity. Scale-volume estimates from brine chemistry, and from stoichiometric amounts of silica dissolved during the acidizing, suggested that the decrease in injectivity was largely due to scale deposition in the near-well formation. Reactive Transport Modeling was used to simulate mineral deposition and injectivity loss. A porosity–permeability relationship was calibrated using observed injection indexes to reproduce the loss of injectivity. The relationship captured very well the steep loss of injectivity, and the simulated amounts of precipitated amorphous silica were consistent with the estimated amounts from field data. Significant precipitation of amorphous silica, and reductions in porosity and permeability, were predicted to occur mainly within a 10 m radius from the well. Injectivity recovery by acid injection was also simulated, and the predicted amount of amorphous silica dissolved by acid was consistent with the estimated amount.
Carl I Steefel - One of the best experts on this subject based on the ideXlab platform.
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Microbially mediated kinetic sulfur isotope fractionation: Reactive Transport Modeling benchmark
Computational Geosciences, 2020Co-Authors: Yiwei Cheng, Sevinc S şengor, Bhavna Arora, Christoph Wanner, Jennifer L. Druhan, Boris M. Breukelen, Carl I SteefelAbstract:Microbially mediated sulfate reduction is a ubiquitous process in many subsurface systems. Isotopic fractionation is characteristic of this anaerobic process, since sulfate-reducing bacteria (SRB) favor the reduction of the lighter sulfate isotopologue (S^32O_4^2−) over the heavier isotopologue (S^34O_4^2−). Detection of isotopic shifts has been utilized as a proxy for the onset of sulfate reduction in subsurface systems such as oil reservoirs and aquifers undergoing heavy metal and radionuclide bioremediation. Reactive Transport Modeling (RTM) of kinetic sulfur isotope fractionation has been applied to field and laboratory studies. We developed a benchmark problem set for the simulation of kinetic sulfur isotope fractionation during microbially mediated sulfate reduction. The benchmark problem set is comprised of three problem levels and is based on a large-scale laboratory column experimental study of organic carbon amended sulfate reduction in soils from a uranium-contaminated aquifer. Pertinent processes impacting sulfur isotopic composition such as microbial sulfate reduction and iron-sulfide reactions are included in the problem set. This benchmark also explores the different mathematical formulations in the representation of kinetic sulfur isotope fractionation as employed in the different RTMs. Participating RTM codes are the following: CrunchTope, TOUGHREACT, PHREEQC, and PHT3D. Across all problem levels, simulation results from all RTMs demonstrate reasonable agreement.
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the mineral dissolution rate conundrum insights from Reactive Transport Modeling of u isotopes and pore fluid chemistry in marine sediments
Geochimica et Cosmochimica Acta, 2006Co-Authors: Kate Maher, Carl I Steefel, Donald J. Depaolo, B E VianiAbstract:Abstract Pore water chemistry and 234U/238U activity ratios from fine-grained sediment cored by the Ocean Drilling Project at Site 984 in the North Atlantic were used as constraints in Modeling in situ rates of plagioclase dissolution with the multicomponent Reactive Transport code Crunch. The Reactive Transport model includes a solid-solution formulation to enable the use of the 234U/238U activity ratios in the solid and fluid as a tracer of mineral dissolution. The isotopic profiles are combined with profiles of the major element chemistry (especially alkalinity and calcium) to determine whether the apparent discrepancy between laboratory and field dissolution rates still exists when a mechanistic Reactive Transport model is used to interpret rates in a natural system. A suite of reactions, including sulfate reduction and methane production, anaerobic methane oxidation, CaCO3 precipitation, dissolution of plagioclase, and precipitation of secondary clay minerals, along with diffusive Transport and fluid and solid burial, control the pore fluid chemistry in Site 984 sediments. The surface area of plagioclase in intimate contact with the pore fluid is estimated to be 6.9 m2/g based on both grain geometry and on the depletion of 234U/238U in the sediment via α-recoil loss. Various rate laws for plagioclase dissolution are considered in the Modeling, including those based on (1) a linear transition state theory (TST) model, (2) a nonlinear dependence on the undersaturation of the pore water with respect to plagioclase, and (3) the effect of inhibition by dissolved aluminum. The major element and isotopic methods predict similar dissolution rate constants if additional lowering of the pore water 234U/238U activity ratio is attributed to isotopic exchange via recrystallization of marine calcite, which makes up about 10–20% of the Site 984 sediment. The calculated dissolution rate for plagioclase corresponds to a rate constant that is about 102 to 105 times smaller than the laboratory-measured value, with the value depending primarily on the deviation from equilibrium. The Reactive Transport simulations demonstrate that the degree of undersaturation of the pore fluid with respect to plagioclase depends strongly on the rate of authigenic clay precipitation and the solubility of the clay minerals. The observed discrepancy is greatest for the linear TST model (105), less substantial with the Al-inhibition formulation (103), and decreases further if the clay minerals precipitate more slowly or as highly soluble precursor minerals (102). However, even several orders of magnitude variation in either the clay solubility or clay precipitation rates cannot completely account for the entire discrepancy while still matching pore water aluminum and silica data, indicating that the mineral dissolution rate conundrum must be attributed in large part to the gradual loss of Reactive sites on silicate surfaces with time. The results imply that methods of mineral surface characterization that provide direct measurements of the bulk surface reactivity are necessary to accurately predict natural dissolution rates.
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Reactive Transport Modeling an essential tool and a new research approach for the earth sciences
Earth and Planetary Science Letters, 2005Co-Authors: Carl I Steefel, Donald J. Depaolo, Peter C. LichtnerAbstract:Abstract Reactive Transport Modeling is an essential tool for the analysis of coupled physical, chemical, and biological processes in Earth systems, and has additional potential to better integrate the results from focused fundamental research on Earth materials. Appropriately designed models can describe the interactions of competing processes at a range of spatial and time scales, and hence are critical for connecting the advancing capabilities for materials characterization at the atomic scale with the macroscopic behavior of complex Earth systems. Reactive Transport Modeling has had a significant impact on the treatment of contaminant retardation in the subsurface, the description of elemental and nutrient fluxes between major Earth reservoirs, and in the treatment of deep Earth processes such as metamorphism and magma Transport. Active topics of research include the development of pore scale and hybrid, or multiple continua, models to capture the scale dependence of coupled Reactive Transport processes. Frontier research questions, that are only now being addressed, include the effects of chemical microenvironments, coupled thermal–mechanical–chemical processes, controls on mineral–fluid reaction rates in natural media, and scaling of Reactive Transport processes from the microscopic to pore to field scale.
