scholarly journals Reactive transport of chemicals in unsaturated soils: numerical model development and verification

2016 ◽  
Vol 53 (1) ◽  
pp. 162-172 ◽  
Author(s):  
Majid Sedighi ◽  
Hywel R. Thomas ◽  
Philip J. Vardon
Keyword(s):  
Numerical Model ◽  
Unsaturated Soils ◽  
Reactive Transport ◽  
Transport Model ◽  
Model Development ◽  
Chemical Diffusion ◽  
New Developments ◽  
Geochemical Model ◽  
Porosity Evolution ◽  
Gas Phases

This paper presents the development of a numerical model for reactive transport of multicomponent chemicals in unsaturated soils. The model has been developed based on a coupled thermal, hydraulic, chemical, and mechanical (THCM) formulation, and extended by the inclusion of geochemical processes under mixed equilibrium and kinetically controlled reactions in–between the solid, aqueous, and gas phases in soil. This has been achieved by coupling the transport model, COMPASS, with the geochemical model, PHREEQC. Key coupling between the geochemical modelling and the flow of chemicals has been established via the inclusion of porosity modification from mineral precipitation–dissolution reactions and the consequential effects on flow processes. Verification of the developed model is addressed via a series of benchmark simulations with a focus on testing the coupling between the transport model and geochemical model. Good results have been achieved for the verification of the theoretical and numerical implementation of the new developments in the model. A simulation is presented to demonstrate the effects of mineral reactions on porosity evolution and chemical diffusion in a low porosity soil. The model developed is an advanced tool for studying the hydrogeochemical processes in unsaturated soils under variable THCM conditions.

scholarly journals Trace element mobility during CO2 storage: application of reactive transport modelling

2019 ◽  
Vol 98 ◽  
pp. 04007
Author(s):  
Dirk Kirste ◽  
Julie K. Pearce ◽  
Sue D. Golding ◽  
Grant K.W. Dawson
Keyword(s):  
Water Quality ◽  
Chemical Composition ◽  
Reactive Transport ◽  
Transport Model ◽  
Co2 Storage ◽  
Chemical Components ◽  
Transport Modelling ◽  
Geochemical Model ◽  
Trace Element Mobility ◽  
The Individual

The geologic storage of CO2 carries both physical and chemical risks to the environment. In order to reduce those risks, it is necessary to provide predictive capabilities for impacts so that strategies can be developed to monitor, identify and mitigate potential problems. One area of concern is related to water quality both in the reservoir and in overlying aquifers. In this study we report the critical steps required to develop chemically constrained reactive transport models (RTM) that can be used to address risk assessment associated with water quality. The data required to produce the RTM includes identifying the individual hydrostratigraphic units and defining the mineral and chemical composition to sufficient detail for the modelling. This includes detailed mineralogy, bulk chemical composition, reactive mineral phase chemical composition and the identification of the occurrence and mechanisms of mobilisation of any trace elements of interest. Once the required detail is achieved the next step involves conducting experiments to determine the evolution of water chemistry as reaction proceeds preferably under varying elevated CO2 fugacities with and without impurities. Geochemical modelling of the experiments is then used for characterising the reaction pathways of the different hydrostratigraphic units. The resultant geochemical model inputs can then be used to develop the chemical components of a reactive transport model.

scholarly journals Reactive transport modelling of long-term interactions between iron and MX-80 bentonite

2021 ◽  
Vol 1 ◽  
pp. 169-170
Author(s):  
M. Carme Chaparro ◽  
Nicolas Finck ◽  
Volker Metz ◽  
Horst Geckeis
Keyword(s):  
Carbon Steel ◽  
Numerical Model ◽  
Reactive Transport ◽  
Transport Model ◽  
Corrosion Products ◽  
Mineral Dissolution ◽  
Secondary Phases ◽  
Short Term ◽  
Complexation Reactions

Abstract. The geological disposal in deep bedrock repositories is the preferred option for the management of high-level radioactive waste. In some of these concepts, carbon steel is considered as potential canister material and bentonites are planned as backfill material to protect metal waste containers. Therefore, a 1D radial reactive transport model has been developed in order to better understand the processes occurring during the long-term iron–bentonite interaction. The conceptual model accounts for diffusion, chemistry of the porewater and aqueous complexation reactions, mineral dissolution/precipitation and absorption, at a constant temperature of 25 ∘C under anoxic conditions. The geometry of the axisymmetric model reflects the canister–bentonite interface and the bentonite. The primary phases considered are montmorillonitic smectite, quartz, muscovite, albite, illite, pyrite and calcite. We assume that carbon steel is composed only of iron. The potential secondary phases considered are from reported experiments, such as magnetite, nontronitic smectite, greenalite, cronstedtite and siderite. The numerical model results suggest that at the iron–bentonite interface, Fe is adsorbed at the smectite surface via ion exchange in the short term and it is consumed by formation of the secondary phases in the long term. Furthermore, calcite precipitates are due to cation exchange in the short term and due to montmorillonitic smectite dissolution in the long term. The numerical model predicts the precipitation of nontronitic smectite, magnetite and greenalite as corrosion products. Results further reveal a significant increase in pH in the long term, whereas dissolution/precipitation reactions result in limited variations of the porosity. Progressing bentonite dissolution owing to the rising pH and concomitantly increasing silicate concentrations in the porewater induce formation of Fe-silicates as corrosion products at the expense of magnetite. A sensitivity analysis has also been performed to study the effect of selected parameters, such as corrosion rate, diffusion coefficient and composition of the porewater, on the corrosion products. Overall, outcomes suggest that pH and concentration of dissolved Si play an important role in corrosion mechanisms. The predicted main secondary phases in the long term are Fe-silicate minerals. Thus, such phases deserve further attention as possible chemical barriers for radionuclide migration in the repository near-field.

scholarly journals Reactive transport model of kinetically controlled celestite to barite replacement

2021 ◽  
Vol 56 ◽  
pp. 57-65
Author(s):  
Morgan Tranter ◽  
Maria Wetzel ◽  
Marco De Lucia ◽  
Michael Kühn
Keyword(s):  
Reactive Transport ◽  
Oil And Gas ◽  
Prediction Models ◽  
Transport Model ◽  
Solid Phase ◽  
A Priori ◽  
Dissolution Kinetics ◽  
Input Concentration ◽  
Geochemical Model ◽  
The Impact

Abstract. Barite formation is of concern for many utilisations of the geological subsurface, ranging from oil and gas extraction to geothermal reservoirs. It also acts as a scavenger mineral for the retention of radium within nuclear waste repositories. The impact of its precipitation on flow properties has been shown to vary by many orders of magnitude, emphasising the need for robust prediction models. An experimental flow-through column setup on the laboratory scale investigating the replacement of celestite (SrSO4) with barite (BaSO4) for various input barium concentrations was taken as a basis for modelling. We provide here a comprehensive, geochemical modelling approach to simulate the experiments. Celestite dissolution kinetics, as well as subsequent barite nucleation and crystal growth were identified as the most relevant reactive processes, which were included explicitly in the coupling. A digital rock representation of the granular sample was used to derive the initial inner surface area. Medium (10 mM) and high (100 mM) barium input concentration resulted in a comparably strong initial surge of barite nuclei formation, followed by continuous grain overgrowth and finally passivation of celestite. At lower input concentrations (1 mM), nuclei formation was significantly less, resulting in fewer but larger barite crystals and a slow moving reaction front with complete mineral replacement. The modelled mole fractions of the solid phase and effluent chemistry match well with previous experimental results. The improvement compared to models using empirical relationships is that no a-priori knowledge on prevailing supersaturations in the system is needed. For subsurface applications utilising reservoirs or reactive barriers, where barite precipitation plays a role, the developed geochemical model is of great benefit as only solute concentrations are needed as input for quantified prediction of alterations.

A Streamlined Workflow From Experimental Analyses to Dynamic Geochemical Modelling

2021 ◽  
Author(s):  
Ahmed M. S. Elgendy ◽  
Simone Ricci ◽  
Elena I. Cojocariu ◽  
Claudio Geloni
Keyword(s):  
Reactive Transport ◽  
Transport Model ◽  
Geochemical Modelling ◽  
Formation Water ◽  
Geochemical Model ◽  
Reactive Transport Model ◽  
Mineral Alteration ◽  
Experimental Analyses ◽  
Water Vaporization

Abstract Dynamic-geochemical model is a powerful instrument to evaluate the geochemical effects on CO2storage capacity, injectivity and long-term containment. The study objective is to apply an integrated multi-step workflow to a carbon capture and storage (CCS) candidate field (offshore), namely hereinafter H field. From experimental analyses, a comprehensive real data-tailored reactive transport model (RTM) has been built to capture the dynamics and the geochemical phenomena (e.g., water vaporization, CO2solubility, mineral alteration) occurring during and after the CO2injection in sedimentary formations. The proposed integrated workflow couples lab activities and numerical simulations and it is developed according to the following steps: Mineralogical-chemical characterization (XRD, XRF and SEM-EDX experimental techniques) of field core samples; Data elaboration and integration to define the conceptual geochemical model; Synthetic brine reconstruction by means of 0D geochemical models; Numerical geochemical modelling at different complexity levels. Field rocks chosen for CO2injection have been experimentally characterized, showing a high content of Fe in clayey, micaceous and carbonate mineralogical phases. New-defined, site-specific minerals have been characterized, starting from real XRD, XRF and SEM-EDX data and by calculation of their thermochemical parameters with a proprietary procedure. They are used to reconstruct synthetic formation water chemical composition (at equilibrium with both rock mineralogy and gas phase), subsequently used in RTM. CO2injection is simulated using 2D radial reactive transport model(s) built in a commercial compositional reservoir simulator. The simulations follow a step-increase in the complexity of the model by adding CO2solubility, water vaporization and geochemical reactions. Geochemical processes impact on CO2storage capacity and injectivity is quantitatively analyzed. The results show that neglecting the CO2solubility in formation water may underestimate the max CO2storage capacity in H field by around 1%, maintaining the same pressure build-up profile. Sensitivities on the impact of formation water salinity on the CO2solubility are presented. In a one thousand years’ time-scale, changes in reservoir porosity due to mineral alteration, triggered by CO2-brine-rock interactions, seem to be minimal in the near wellbore and far field. However, it has been seen that water vaporization with the associated halite precipitation inclusion in the simulation models is recommended, especially at high-level of formation brine salinity, for a reliable evaluation of CO2injectivity related risks. The proposed workflow provides a new perspective in geochemical application for CCS studies, which relies on novel labs techniques (analyses automation), data digitalization, unification and integration with a direct connection to the numerical models. The presented procedure can be followed to assess the geochemical short-and long-term risks in carbon storage projects.

Geochemical Model of the Granite-Bentonite-Groundwater at Äspö (LOT Experiment)

2003 ◽  
Vol 807 ◽  
Author(s):  
C. Domènech ◽  
D. Arcos ◽  
J. Bruno ◽  
O. Karnland ◽  
A. Muurinen
Keyword(s):  
Temperature Gradient ◽  
Temperature Effect ◽  
Reactive Transport ◽  
Transport Model ◽  
Geochemical Modelling ◽  
Effect Of Temperature ◽  
Geochemical Evolution ◽  
Geochemical Model ◽  
Reactive Transport Model

ABSTRACTA geochemical modelling of one of the experimental parcels of the LOT experiment (Äspö, Sweden) is presented. The model consists on a 2D reactive transport model of a perpendicular section of the experimental borehole with a stationary temperature gradient ranging from 130 to 15°C. The results of the model show that temperature has an important effect on the geochemical evolution of the system. Due to the temperature effect, anhydrite replaces gypsum and hematite precipitates instead of Fe(OH)3(am). Calcite and siderite dissolve in the warmer part of bentonite; whereas a major replacement of Na by Ca in the bentonite takes place close to the bentonite-granite boundary. pH is buffered by the equilibrium with calcite, although the effect of temperature leads to a decrease in pH.

scholarly journals Large‐Scale Experiments in Microbially Induced Calcite Precipitation (MICP): Reactive Transport Model Development and Prediction

2018 ◽  
Vol 54 (1) ◽  
pp. 480-500 ◽  
Author(s):  
Mohamed K. Nassar ◽  
Deviyani Gurung ◽  
Mehrdad Bastani ◽  
Timothy R. Ginn ◽  
Babak Shafei ◽  
...  
Keyword(s):  
Reactive Transport ◽  
Large Scale ◽  
Transport Model ◽  
Model Development ◽  
Calcite Precipitation ◽  
Microbially Induced Calcite Precipitation ◽  
Reactive Transport Model

scholarly journals Numerical Modeling of a Laboratory-Scale Waste Rock Pile Featuring an Engineered Cover System

Minerals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 652
Author(s):  
Katherine E. Raymond ◽  
Nicolas Seigneur ◽  
Danyang Su ◽  
Bissé Poaty ◽  
Benoît Plante ◽  
...  
Keyword(s):  
Numerical Model ◽  
Laboratory Experiment ◽  
Reactive Transport ◽  
Transport Model ◽  
Internal Flow ◽  
Infiltration Rate ◽  
Mineral Weathering ◽  
Waste Rock ◽  
Water Diversion ◽  
Cover System

Improved design to reduce contaminant mass loadings from waste rock piles is an increasingly important consideration. In certain cases, an engineered cover system containing a flow control layer (FCL) may be used to mitigate the release of metals out of a pile using capillary barrier effects (CBEs), diverting water away from reactive materials below. In this study, a reactive transport model was calibrated to observational data from a laboratory experiment designed to evaluate a cover system. The results show that the numerical model is capable of capturing flow rates out of multiple drainage ports and matching key effluent concentrations by including the spatial distribution of hydraulic parameters and mineral weathering rates. Simulations were also useful for characterizing the internal flow pathways within the laboratory experiment, showing the effectiveness of the cover in diverting the flow away from the reactive waste rock and identifying secondary CBEs between different rock types. The numerical model proved beneficial in building an improved understanding of the processes controlling the metal release and conceptualizing the system. The model was expanded to investigate the robustness of the cover system as a function of the applied infiltration rate, supporting that water diversion will occur with infiltration rates representative of field conditions.

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