Academic literature on the topic 'PhreeqC numerical simulations'

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.

CO2 mineralization is a long-term and secure solution for geological CO2 storage that primarily depends on the CO2–brine–rock interaction during CO2 sequestration in subsurface formations. In this study, lab experiments were conducted to investigate the CO2–brine–rock interaction over short timescales, and numerical simulations were performed to reveal dynamic interactions and equilibrium interactions by applying TOUGHREACT and PHREEQC, respectively. In the experiments, the main ions of HCO3− and Ca2+ were detected in the solution, and calcite dissolution and dawsonite precipitation were observed from SEM images. The simulation results showed that the CO2 dissolution and the solution pH were affected by the temperatures, pressures, types of solutions, and solution concentrations and were further influenced by mineral dissolution and precipitation. The results of the equilibrium simulation showed that the dissolved minerals were albite, anhydrite, calcite, Ca-montmorillonite, illite, K-feldspar, and chlorite, and the precipitated minerals were dolomite, kaolinite, and quartz, which led to HCO3−, K+, and Na+ being the main ions in solutions. The results of the dynamic simulation showed that calcite and dolomite dissolved in the early period, while other minerals began to dissolve or precipitate after 100 years. The dissolved minerals were mainly albite, kaolinite, K-feldspar, and chlorite, and precipitated minerals were Ca-montmorillonite, illite, and quartz. Anhydrite and pyrite did not change during the simulation period, and the main ions were HCO3−, Na+, Ca2+, and Mg2+ in the simulation period. This study provides an effective approach for analyzing the CO2–brine–rock interaction at different stages during CO2 storage, and the results are helpful for understanding the CO2 mineralization processes in deep saline aquifers.

Fractures are major flow paths for solute transport in fractured rocks. Conducting numerical simulations of reactive transport in fractured rocks is a challenging task because of complex fracture connections and the associated nonuniform flows and chemical reactions. The study presents a computational workflow that can approximately simulate flow and reactive transport in complex fractured media. The workflow involves a series of computational processes. Specifically, the workflow employs a simple particle tracking (PT) algorithm to track flow paths in complex 3D discrete fracture networks (DFNs). The PHREEQC chemical reaction model is then used to simulate the reactive transport along particle traces. The study illustrates the developed workflow with three numerical examples, including a case with a simple fracture connection and two cases with a complex fracture network system. Results show that the integration processes in the workflow successfully model the tetrachloroethylene (PCE) and trichloroethylene (TCE) degradation and transport along particle traces in complex DFNs. The statistics of concentration along particle traces enables the estimations of uncertainty induced by the fracture structures in DFNs. The types of source contaminants can lead to slight variations of particle traces and influence the long term reactive transport. The concentration uncertainty can propagate from parent to daughter compounds and accumulate along with the transport processes.

One of the challenges of the present century is to limit the greenhouse gas emissions for the mitigation of climate change which is possible for example by a transitional technology, CO2 geological storage. Clay minerals are considered to be responsible for the low permeability and sealing capacity of caprocks sealing off stored CO2. However, their reactions are not well understood for complex simulations. This work aims to create a kinetic geochemical model of Na-montmorillonite standard SWy-2 supported by solution and mineral composition results from batch experiments. Such experimentally validated numerical models are scarce. Four 70-hours experiments have been carried out at atmospheric conditions, and with CO2 supercritical phase at 100 bar and 80 °C. Solution samples have been taken during and after experiments and their compositions were measured by ICP-OES. The treated solid phase has been analyzed by XRD and ATR-FTIR and compared to in-parallel measured references (dried SWy-2). Kinetic geochemical modelling of the experimental conditions has been performed by software PHREEQC. Experiments and models show fast reactions under the studied conditions and increased reactivity in presence of scCO2. Solution composition results cannot be described by the change of the uncertain reactive surface area of mineral phases. By considering the clay standard’s cation exchange capacity divided proportionally among interlayer cations of Na-montmorillonite, the measured variation can be described on an order of magnitude level. It is furthermore indicated that not only the interlayer cations take part in this process but a minor proportion of other, structural ions as well, differently in the reference and scCO2 environments.

Geochemical modeling has been frequently used to understand and interpret water-rock interactions in sedimentary basins. Thermodynamic data, kinetic parameters, numerical methods, boundary history, and boundary conditions are factors affecting any geochemical modeling system. In the present study, we have attempted to establish a geochemical speciation model by comparing the interaction of formation water and carbonate rock in the carbonate depositional settings of Cambrian successions of Bachu and Tarim area. A comparative study of geochemical speciation has been performed using four different software: PHREEQCTM, GWBTM, TOUGHREACTTM, and GEODELING. GEODELING is a geochemical code simulator that we have developed, and the details are presented further in this work. All the software has been analyzed minutely, considering the distribution, mobility, and availability of chemical species in geological environments. Very similar results in speciation are observed while working with low-temperature systems. A discrepancy can be observed in the results while working with high temperatures. However, a thorough Newton-Raphson formulation, scaling of algebraic equations and master-species switching helps to reduce the possibility of failures of the numerical method used in PHREEQCTM.

Abstract. Many types of geologic subsurface utilisation are associated with fluid and heat flow as well as simultaneously occurring chemical reactions. For that reason, reactive transport models are required to understand and reproduce the governing processes. In this regard, reactive transport codes must be highly flexible to cover a wide range of applications, while being applicable by users without extensive programming skills at the same time. In this context, we present an extension of the Open Source and Open Access TRANSPORT Simulation Environment, which has been coupled with the geochemical reaction module PHREEQC, and thus provides multiple new features that make it applicable to complex reactive transport problems in various geoscientific fields. Code readability is ensured by the applied high-level programming language Python which is relatively easy to learn compared to low-level programming languages such as C, C++ and FORTRAN. Thus, also users with limited software development knowledge can benefit from the presented simulation environment due to the low entry-level programming skill requirements. In the present study, common geochemical benchmarks are used to verify the numerical code implementation. Currently, the coupled simulator can be used to investigate 3D single-phase fluid and heat flow as well as multicomponent solute transport in porous media. In addition to that, a wide range of equilibrium and nonequilibrium reactions can be considered. Chemical feedback on fluid flow is provided by adapting porosity and permeability of the porous media as well as fluid properties. Thereby, users are in full control of the underlying functions in terms of fluid and rock equations of state, coupled geochemical modules used for reactive transport, dynamic boundary conditions and mass balance calculations. Both, the solution of the system of partial differential equations and the PHREEQC module, can be easily parallelised to increase computational efficiency. The benchmarks used in the present study include density-driven flow as well as advective, diffusive and dispersive reactive transport of solutes. Furthermore, porosity and permeability changes caused by kinetically controlled dissolution-precipitation reactions are considered to verify the main features of our reactive transport code. In future, the code implementation can be used to quantify processes encountered in different types of subsurface utilisation, such as water resource management as well as geothermal energy production, as well as geological energy, CO2 and nuclear waste storage.

Summary Single-well chemical tracer (SWCT) is the most commonly used field method to determine oil or water saturation in one-well enhanced-oil-recovery (EOR) pilots. Because hydrolysis of an ester, which is the main part of the method, leads to forming acid as well as alcohol, the equilibrium state of the reservoir is disturbed, and thus the pH changes. It is generally accepted that the hydrolysis-reaction rate is mainly dependent on the pH and temperature. Therefore, it is required to know the extent to which this dependency might affect the shape of the product-tracer profiles and the numerical interpretation of the field-test data for computing residual oil saturation (Sor). In this study, this notion has been investigated by coupling a multiphase-flow simulator to the geochemistry package PHREEQC (Parkhust and Appelo 2013). In this study, the PHREEQC geochemical simulator has been used to illustrate the extent to which different parameters might affect the pH variation during the test. The PHREEQC database has been modified to take the ester-hydrolysis reaction into account by adding the ester, alcohol, and acid-product species. The hydrolysis-reaction mechanisms of ester have also been programmed to account for the dependency of the hydrolysis reaction on the pH. Also, because ester partitions into the oil phase and travels behind the water phase (i.e., Darcy velocity), performing two-phase flow would be necessary to highlight the significance of the pH dependency of the hydrolysis-reaction rate on the tracer profiles. For doing that, a multiphase Buckley-Leverett (BL) flow simulation is coupled with IPhreeqc, which is an open-source module of the PHREEQC geochemical package. Then, a California Turbidite SWCT test has been re-evaluated to verify the approach. At the end, the geochemistry of a reservoir with an almost weak resistance (high temperature and weak buffer capacity) against pH variation in the SWCT test has been studied using the geochemical-based approach. The results show that the variation of the hydrolysis rate with pH could affect mainly the tail edge of the predicted tracer profiles, and it could marginally affect the apex of the profiles; however, it might affect the interpreted value of the Sor measurement as the resistance against pH variation becomes weaker. In these conditions, adapting the SWCT-test designs (i.e., shut-in time and injecting lower concentration of ester) could diminish the pH variation. The pH dependency of the hydrolysis-reaction rate is recommended for the numerical interpretation of the field SWCT-test data. The results of this study can be used to minimize the uncertainties of the SWCT tests and to improve the reliability of the Sor measurements.

Shallow salt water in the inland plain has huge development potential. Taking saline water area in Sungeng Town, Jiyang County as an example, based on field water quality and water table tests., tracing test, methods such as mathematical statistical, hydrochemistry diagram of piper and numerical simulation by PHREEQC are used to analyze synthetically. 6862 groups data were studied. Results showed: (1) The groundwater presents typically “weather - evaporation” type, chemistry type is Cl.SO4-Mg.Na. and Cl.SO4-Na.Mg type. (2) In area of inland saline water presents characteristics of lagging water flow with high clay content in aquifer medium. Groundwater mineralization is obvious. (3) Hydrogeochemistry actions such as evaporation, alternate adsorption and water-rock interaction are the primary cause of the forming complex hydrochemistry type. The unique groundwater circulation characteristics of inland plains saltwater area makes water dynamic being relatively stable.

Summary The interest in modeling geochemical reactions has increased significantly for different improved-oil-recovery processes such as alkali/surfactant/polymer (ASP) flood, low-salinity waterflood, and ethylenediaminetetraacetic acid (EDTA) injection as a sacrificial agent in hard brine. Numerical simulation of multiphase flow coupled with geochemical reactions is challenging because of complex and coupled aqueous, aqueous/solid, and aqueous/oleic reactions. These reactions have significant impact upon oil recovery, and hence a robust geochemical simulator is important. UTCHEM (2000) is a chemical-flooding reservoir simulator with geochemical-modeling capability. Nevertheless, one major limitation in the geochemical-reactive engine of UTCHEM is assuming the activities of reactive species is equal to unity. In fact, the activity coefficients are strongly nonlinear functions of the ionic strength of solution. One approach to tackle this deficiency was to couple UTCHEM (flow and transport) with IPhreeqc (a geochemical reactive engine) (Kazemi Nia Korrani et al. 2013). However, the simulator proved to be computationally expensive. Therefore, it is desirable to improve the geochemical- reactive engine within UTCHEM. This paper presents the improvement of the geochemical-reactive engine in UTCHEM including implementing different activity-coefficient models for different reactive species, cation-exchange reactions, and numerical convergence. Certain unknown concentrations are eliminated from the elemental mass-balance equations and the reaction equations to reduce the computational burden. The Jacobian matrix and right-hand side of the linear-system equation in the Newton-Raphson method are updated accordingly in the Newton-Raphson method for performing the batch-reaction calculation. A low-salinity-waterflood case is presented to validate the updated UTCHEM against PHREEQC (Parkhurst and Appelo 1999) and UTCHEM-IPhreeqc. The simulation studies indicated that the updated geochemical simulator succeeds in tackling the inaccuracy concerned in the original UTCHEM. Also, the updated version is more efficient compared with PHREEQC and UTCHEM-IPhreeqc with the same degree of accuracy. The updated geochemical simulator is then applied to model an ASP coreflood in which EDTA is used as a sacrificial agent to chelate calcium and magnesium ions. The experimental data of pH, oil recovery, and pressure drop were successfully history matched with predictions of the effluent concentrations of calcium and magnesium ions. A synthetic 3D ASP pilot case is successfully simulated considering effects of acid equilibrium reaction constant on oil recovery.

Abstract Deep geological disposal is the preferred solution for long-term storage of radioactive waste in many countries. In a deep repository, cementitious materials are widely used in the structure and buffer/backfill of the repository for the stabilisation of the hazardous materials. The cement acts as a physical barrier and also contributes chemically to waste containment by buffering the groundwater to a high pH, limiting the solubility of many radionuclides. This paper describes an experimental and modelling study which evaluates the geochemical interaction between young cement leachate (YCL, pH = 13) and a generic hard rock (in this case Hollington sandstone, representing a ‘hard’ host rock) during permeation with the leachate, as it drives mineralogical changes in the system. One-dimensional reactive transport was modelled using a mixing cell approach within the PHREEQC geochemical code to identify the essential parameters and understand and scale up the effect of variations in these parameters on the observed geochemical processes. This study also focused on the effects of variable porosity, reactive surface area and pore volume on improving the modelling of rock alteration in the system compared to conventional models that assume constant values for these properties. The numerical results showed that the interaction between the injected hyper-alkaline leachate and the sandstone sample results in a series of mineralogical reactions. The main processes were the dissolution of quartz, kaolinite and k-feldspar which was coupled with the precipitation of calcium silicate hydrate gel and tobermorite-14A (C–S–H), prehnite (hydrated silicate), saponite-Mg (smectite clay) and mesolite (Na–Ca zeolite). The simulation showed that the overall porosity of the system increased as primary minerals dissolve and no stable precipitation of the secondary C–S–H /C–A–S–H phases was predicted. The variable porosity scenario provides a better fitting to experimental data and more detailed trends of chemistry change within the column. The time and the number of moles of precipitated secondary phases were also improved which was related to greater exposure surface area of the minerals in the sandstone sample to the YCL. Article Highlights The drop in calcium, aluminium and silicate concentrations is mainly due to the formation of calcium silicate hydrate and zeolite minerals as secondary phases. The simulation showed that the overall porosity of the system increased as primary minerals dissolve and no stable precipitation of the secondary C–S–H /C–A–S–H phases was predicted. The dissolution of primary minerals and the precipitation of secondary C–S–H phases had a minimal effect on the pH values, and this was controlled mainly by the initial fluid chemistry. The variable porosity scenario provides a better fitting to experimental data and more detailed trends of chemistry change within the column.

Le stockage du CO2 dans les aquifères salins profonds a été reconnu comme l'une des voies les plus prometteuses pour atténuer les émissions atmosphériques de CO2 et répondre ainsi aux enjeux du changement climatique. Cependant, l’injection du CO2 dans le milieu poreux perturbe considérablement son équilibre thermodynamique. La zone proche du puits d’injection est particulièrement impactée avec une forte réactivité géochimique associée à d’intenses échanges thermiques. Cela a un impact majeur sur l’injectivité du réservoir et l’intégrité du stockage. A ces effets s’ajoute une complexité supplémentaire liée à la présence de deux phases non miscibles : la saumure et le CO2. Ces effets conduisent à des processus Thermo-Hydro-Mécaniques-Chimiques (THMC) fortement couplés, dont les interprétations ne sont pas encore abouties ni formellement implémentées dans les modèles numériques.Ce travail de thèse, associant des mesures expérimentales et des modélisations numériques, porte sur l’étude du couplage entre les gradients thermiques et les processus diffusifs de transport réactif se déroulant dans les aquifères salins, notamment dans la zone proche du puits d’injection. Nous avons étudié les échanges entre une phase froide CO2 anhydre qui s’écoule dans des zones de forte perméabilité, et une phase aqueuse salée chaude piégée dans la porosité de la roche. La stratégie de l'étude commence par une approche simple en milieu libre sans flux de CO2 afin d'étudier la réactivité des solutions salines de différentes compositions chimiques et d’évaluer l'impact d'un gradient thermique sur ce réseau réactionnel.Nous avons développé une cellule expérimentale permettant de superposer 2 à 3 couches de solution de concentration et composition chimique différentes. L’analyse de la lumière diffusée par les fluctuations de non-équilibre de la concentration et de la température permet de remonter aux coefficients de diffusion des sels dans l’eau. Nos résultats sont en bon accord avec les valeurs de la littérature. Pour ce qui est de l’étude du transport réactif diffusif, l’analyse du contraste des images a permis de mettre en évidence le fait que la précipitation de minéral, par mise en contact de deux couches aqueuses de sels réactifs, s’accompagne d’une instabilité convective qui s’estompe dans le temps. La modélisation numérique des résultats expérimentaux avec PHREEQC par une approche de diffusion multi-espèce hétérogène permet de rendre compte des instabilités convectives. Différents gradients de température ont été appliqués au système réactif, tout en conservant une température moyenne de 25 °C. Les observations expérimentales et les interprétations numériques montrent que le gradient de température n'a pas d’influence significative sur le comportement du système.Ensuite, nous avons étudié numériquement le processus de dessiccation (évaporation de l’eau) à l’interface entre une saumure piégée dans la porosité de la roche et du CO2 circulant dans une structure porale drainante, simulant les conditions de l’aquifère du Dogger du bassin parisien. Un modèle couplant l’évaporation de l’eau dans le flux de CO2 et la diffusion multi-espèces hétérogène des sels prévoit l’apparition d’un assemblage minéral au niveau du front d’évaporation, principalement composé d’halite et d’anhydrite. La modélisation de ce phénomène à l’échelle du réservoir nécessite la prise en compte de la vitesse d’évaporation en fonction du taux d’injection du CO2 et de l’évolution de la porosité au niveau de l’interface.Ce travail de thèse a permis de mettre en évidence plusieurs phénomènes physico-chimiques, thermo-physiques et de transport diffusif aux interfaces de phase. Ce qui ouvre de nouvelles perspectives d’amélioration des approches numériques et de modélisation à grande échelle notamment du proche puits d’injection du CO2 et des réservoirs de stockage géologique et soutenir les futurs développements industriels et technologiques pour la transition écologique
CO2 storage in deep saline aquifers has been recognised as one of the most promising ways to mitigate atmospheric CO2 emissions and thus respond to the challenges of climate change. However, the injection of CO2 into the porous medium considerabely disturbs its thermodynamic equilibrium. The near-well injection zone is particularly impacted with a strong geochemical reactivity associated with intense heat exchanges. This has a major impact on injectivity of the reservoir and the integrity of the storage. In addition to these effects, there is the added complexity of the presence of two immiscible phases: brine (wetting fluid) and CO2 (non-wetting fluid). These effects lead to highly coupled Thermo-Hydro-Mechanical-Chemical (THMC) processes, whose interpretations have not yet been completed nor formally implemented into the numerical models.This thesis work, combining experimental measurements and numerical modelling, focuses on the study of the coupling between the thermal gradients and the diffusive reactive transport processes taking place in the deep saline aquifers, particularly in the near-well injection zone. We studied the exchanges between a cold anhydrous CO2 phase flowing in high permeability zones, and a hot salty aqueous phase trapped in the porosity of the rock. The strategy of the study starts with a simple approach in a free medium without CO2 flow, in order to study the reactivity of saline solutions of different chemical compositions, and to evaluate the impact of a thermal gradient on this reaction network.We have developed an experimental cell that allow to superimpose 2 to 3 layers of solution of different concentration and chemical composition. The analysis of the light scattered by the non-equilibrium fluctuations of concentration and temperature allows to obtain the diffusion coefficients of salts in water. Our results are in good agreement with literature values. Regarding the study of diffusive reactive transport, the analysis of the contrast of the images allowed us to highlight the fact that the precipitation of minerals, obtained by superimposing two aqueous layers of reactive, is accompanied by a convective instability that fades with time. Numerical modelling of the experimental results with PHREEQC using a heterogeneous multicomponent diffusion approach has allowed us to account for these convective instabilities. Different temperature gradients were applied to the reactive system, while keeping a mean temperature of 25 °C. The experimental observations and numerical interpretations swhow that the temperature gradient has no significant influence on the behaviour of the system. Subsequently, we numerically studied the desiccation process (evaporation of water) at the interface between a brine trapped in the rock porosity and the CO2 flowing in a draining pore structure, simulating the conditions of the Dogger aquifer of the Paris basin. A model coupling the evaporation of water in the CO2 stream and the heterogeneous multicomponent diffusion of salts predicts the appearance of a mineral assemblage at the evaporation front, mainly composed by halite and anhydrite. Modelling this phenomenon at the reservoir scale would requires taking into account the evaporation rate as a function of the CO2 injection rate and the change in porosity at the interface.This thesis work has made it possible to highlight several physicochemical, thermophysical and diffusive transport phenomena at phase interfaces. This opens up new perspectives for improving numerical approaches and large-scale modelling, in particular of near-well injection of CO2 and geological storage reservoirs, and supports future industrial developments and technologies for the ecological transition

La modélisation du transport réactif dans les milieux poreux implique la simulation de plusieurs processus physico-chimiques : écoulement de phases fluides, transport de chaleur, réactions chimiques entre espèces en phases identiques ou différentes. La résolution du système d'équations qui décrit le problème peut être obtenue par une approche soit totalement couplée soit découplée. Les approches découplées simplifient le système d'équations en décomposant le problème sous-parties plus faciles à gérer. Chacune de ces sous-parties peut être résolue avec des techniques d'intégration appropriées. Les techniques de découplage peuvent être non‑itératives (operator splitting methods) ou itératives (fixed‑point iteration), chacunes ayant des avantages et des inconvénients. Les approches non‑iteratives génèrent une erreur associée à la séparation des sous­-parties couplées, et les approaches itératives peuvent présenter des problèmes de convergence. Dans cette thèse, nous développons un code sous licence libre en langage MATLAB (https://github.com/TReacLab/TReacLab) dédie à la modélisation du la problématique de la carbonatation atmosphérique du béton, dans le cadre du stockage de déchets de moyenne activité et longue vie en couche géologique profonde. Le code propose un ensemble d'approche découplée : classique, comme les approches de fractionnement séquentiel, alternatif ou Strang, et moins classique, comme les approches de fractionnement additif ou par répartition symétrique. En outre, deux approches itératives basées sur une formulation spécifique (SIA CC et SIA TC) ont également été implémentées. Le code été interfacé de manière générique avec différents solveurs de transport (COMSOL, pdepe MATLAB, FVTool, FD scripts) et géochimiques (iPhreeqc, PhreeqcRM). Afin de valider l'implémentations des différentes approches, plusieurs bancs d'essais classiques dans le domaine du transport réactif ont été utilises avec succès. L'erreur associée à la combinaison du fractionnement de l'opérateur et des techniques numériques étant complexe à évaluer, nous explorons les outils mathématiques existants permettant de l'estimer. Enfin, nous structurons le problème de la carbonatation atmosphérique et présentons des simulations préliminaires, en détaillant les problèmes pertinents et les étapes futures à suivre
Reactive transport modeling in porous media involves the simulation of several physico‑chemical processes: flow of fluid phases, transport of species, heat transport, chemical reactions between species in the same phase or in different phases. The resolution of the system of equations that describes the problem can be obtained by a fully coupled approach or by a decoupled approach. Decoupled approaches can simplify the system of equations by breaking down the problem into smaller parts that are easier to handle. Each of the smaller parts can be solved with suitable integration techniques. The decoupling techniques might be non‑iterative (operator splitting methods) or iterative (fixed‑point iteration), having each its advantages and disadvantages. Non‑iterative approaches have an error associated with the separation of the coupled effects, and iterative approaches might have problems to converge. In this thesis, we develop an open‑source code written in MATLAB (https://github.com/TReacLab/TReacLab) in order to model the problematic of concrete atmospheric carbonation for an intermediate‑level long‑lived nuclear waste package in a deep geological repository. The code uses a decoupled approach. Classical operator splitting approaches, such as sequential, alternating or Strang splitting, and less classical splitting approaches, such as additive or symmetrically weighted splitting, have been implemented. Besides, two iterative approaches based on an specific formulation (SIA CC, and SIA TC) have also been implemented. The code has been interfaced in a generic way with different transport solvers (COMSOL, pdepe MATLAB, FVTool, FD scripts) and geochemical solvers (iPhreeqc, PhreeqcRM). In order to validate the implementation of the different approaches, a series of classical benchmarks in the field of reactive transport have been solved successfully and compared with analytical and external numerical solutions. Since the associated error due to the combination of operator splitting and numerical techniques may be complex to assess, we explore the existing mathematical tools used to evaluate it. Finally, we frame the atmospheric carbonation problem and run preliminary simulations, stating the relevant problems and future steps to follow

In my thesis work, 0D geochemical numerical models were implemented in order to qualitatively and quantitatively understand the results of a set of experiments obtained from a physical model, to simulate the concretion effects on high enthalpy geothermal wells. In particular a set of flow-through simulation results based on the physical model were used to reproduce the precipitation of metallic copper resulting from steel corrosion in a geothermal production well positioned at Groß Schönebeck, Germany. The numerical models were implemented with PHREEQC hydrogeochemical simulator (Appelo and Parkhurst, 1999). Although the predications obtained from the numerical simulations have not systematically matched the experimental data obtained by physical model, nevertheless, very useful information on the behaviours of these kind of processes has been obtained. Now this useful information is used at the German Research Center for Geosciences (GFZ) in Potsdam to develop more accurate new research lines.

The Biscayne Aquifer is a primary source of water supply in Southeast Florida. As a coastal aquifer, it is threatened by saltwater intrusion (SWI) when the natural groundwater flow is altered by over-pumping of groundwater. SWI is detrimental to the quality of fresh groundwater sources, making the water unfit for drinking due to mixing and reactions with aquifer minerals. Increasing water demand and complex environmental issues thus force water utilities in South Florida to sustainably manage saltwater intrusion and develop alternative water supplies (e.g., aquifer storage and recovery, ASR). The objectives of this study were to develop and use calibrated geochemical models to estimate water quality changes during saline intrusion and during ASR in south Florida. A batch-reaction model of saltwater intrusion was developed and important geochemical reactions were inferred. Additionally, a reactive transport model was developed to assess fate and transport of major ions and trace metals (Fe, As) at the Kissimmee River ASR. Finally, a cost-effective management of saltwater intrusion that involves using abstraction and recharge wells was implemented and optimized for the case of the Biscayne Aquifer. Major processes in the SWI areas were found to be mixing and dissolution-precipitation reactions with calcite and dolomite. Most of the major ions (Cl, Na, K, Mg, SO4) behaved conservatively during ASR while Ca and alkalinity were affected by carbonate reactions and cation exchange. A complex set of reactions involving thermodynamic equilibrium, kinetics and surface complexation reactions was required in the ASR model to simulate observed concentrations of Fe and As. The saltwater management model aimed at finding optimal locations and flow rates for abstraction and recharge wells. Optimal solutions (i.e., minimum total salt and total cost Pareto front) were produced for the Biscayne Aquifer for scenarios of surface recharge induced by climate change-affected precipitation. In general, abstraction at the maximum rate near the coast and artificial recharge at locations much further inland were found to be optimal. Knowledge developed herein directly supports the understanding of SWI caused by anthropogenic stressors, such as over-pumping and sea level rise, on coastal aquifers.

Abstract The demand for large scale energy storage has been increasing for the integration of highly fluctuating energy production from renewables. Depleted gas fields are among the most suitable candidates for underground hydrogen storage, with well-known high-quality reservoir petrophysical characteristics, huge storage capacities and good sealing. However, biogeochemical interactions of hydrogen with rock-brine-resident gas could lead to hydrogen degradation as it is a favoured substrate for many anaerobic microorganisms. Thus, reservoir-scale predictive tools able to simulate these complex and tightly coupled physical, chemical, and biological phenomena are necessary for better investment decisions. A novel approach to model underground hydrogen storage biogeochemical reactions in a commercial compositional reservoir simulator is presented, tested, and analyzed. The significance of this work is the inclusion of bacterial exponential growth and decay in the numerical models which is essential for a more realistic prediction of hydrogen behaviour in subsurface. This has been embedded in a well-known reservoir simulation tool, GEM unconventional and compositional reservoir simulator, frequently used in the oil and gas industry for subsurface 3D problems. First, a conceptual biogeochemical model was conceived, and the underlying reactions were identified. The reaction mechanisms allow to consider the tight coupling between biochemical and geochemical processes. Then, a set of numerical cases, based on the conceptual biogeochemical model, were simulated in batch mode using two software: PHREEQC geochemical code and GEM reservoir simulator. The cases follow a step increase in the model complexity by adding bacterial growth and decay. GEM does not support the Monod kinetics which describes the microorganism's growth; thus, a tuning of the Arrhenius equation parameters was performed to match the Monod formula over the substrate(s) concentrations of interest. Finally, the Arrhenius formulation was further customized to include bacterial exponential growth and decay by an adequate bacterial stoichiometry implementation in which the bacteria was defined as molar aqueous component. The numerical simulations proved that a properly tuned Arrhenius kinetic model may reproduce the Monod dynamics with acceptable accuracy. In addition, for the most complete and complex case (D), GEM results show a good benchmark with PHREEQC ones, attesting the fact that a properly customized Arrhenius model, integrating the kinetics of both substrates and bacteria, and being modelled with a single (or two if decay is also considered) stoichiometric reaction, is able to appropriately capture underground hydrogen storage biogeochemical reactivity. In the cases considered, results show that the geochemistry has a limited impact on the biochemical process. However, the impact depends on pure geochemical limiting factors, i.e., presence of free protons. The study recommends that the estimation of kinetic parameters of biological processes (e.g., Methanogenesis) should be prioritized in future experimental campaigns to better understand their influence on underground hydrogen storage.

Abstract Global warming and climate change are influenced by the discharge of carbon dioxide into the Earth's atmosphere. CO2 can be injected into underground storage locations such as depleted oil and gas reservoirs or saline aquifers to reduce emission impacts. Injected CO2 will be located next to the reservoir phases in place: brine, pore surface minerals, and any residual oil. CO2 in brine forms carbonic acid, which could affect the stability of minerals. Short-term and long-term geochemical alteration processes should be screened to improve the understanding of mineral dissolution and in-situ mineralization mechanisms, giving improved quality of the numerical models needed for large-scale simulations. This study investigated the chemical interactions between sandstone, chalk minerals, and carbonated water (CW) at static high-pressure/temperature conditions. Feldspar and carbonate minerals batches with different surface areas were exposed to CW for 1 and 3 months. Fluid properties before and after CW exposure were measured using ion chromatography (IC) and pH tests, and the integrity of the rock grains was studied by scanning electron microscopy (SEM) and a laser diffraction analyzer. Subsequently, the compositions of the exposed minerals were examined using energy-dispersive X-ray spectrometry (EDX). In addition, CW core flooding tests were conducted on outcrop chalk, as chalk was the mineral showing the highest reactivity in the static batch experiments. At the final stage, the static CW exposure test results were modeled by PHREEQC. The results showed that the static batch experiments only revealed minor dissolution effects in chalk after CW exposure. Dynamic core flooding tests using an outcrop chalk core showed that injection of CW can cause higher rock dissolution at the inlet of the core. Exposing reactive minerals to CW can cause chalk dissolution and ionic exchange in feldspars. However considerable changes in sample integrity and grain geometry during the experiments were not observed. PHREEQC modeling made an acceptable match between the experimental and the simulated data. This research shows that the dominant mechanisms between CW and the exposed minerals were ionic exchange and mineral dissolution. When these processes consume CO2, it leads to improved CO2 storage due to increased dissolution trapping. The study's results can be used to assess the integrity of the storing bed minerals after CW exposure.

Abstract Smart Water Assisted Foam (SWAF) flooding is a promising and an emerging synergic enhanced oil recovery (EOR) technique that combines smart water and foam injections. This technique works best in carbonates with mixed-to-oil wet wettability, where smart water (SW) alters the rock wettability towards a water-wetting state and stabilizes the foam lamellae, and surfactant aqueous solution (SAS) reduces interfacial tension (IFT) leading to improvement in oil recovery. This paper provides more insight and better understanding of the controlling mechanisms behind incremental oil recovery by this hybrid technique through a combined numerical and experimental approach. In this study, a mechanistic approach using surface complexation modeling (SCM) and DLVO theory was followed for modeling this hybrid technique, which aids in a better understanding of crude oil/brine/rock (COBR-system) interactions. The SCM considered the SAS-rock and SAS-oil interactions, which enabled improved prediction of rock wettability alteration through capturing surface complexes and surface potentials in the COBR-system. The Phreeqc simulator was used and the simulations were performed at 80°C. The proposed SCM was validated against experimentally measured contact angle and zeta potential measurements. Subsequently, to identify the best SAS formulations that promote stable foam generation and its propagation inside porous media during coreflood, foamability and foam stability tests were performed. Successful combination of SAS and Gas (i.e., SAG) candidates were confirmed by conducting coreflooding tests. Furthermore, the CMG-STARS simulator was used to history match a coreflooding experiment with providing insights into the relative permeability curves and the related interpolation parameters. Based on the numerical and experimental results, a stable water film was noted for low salinity case of MgCl2 solution where the same surface potential signs were obtained for both rock-brine and brine-oil interfaces. Also, the maximum contact angle reduction for the single ionic compounds was demonstrated by MgCl2 (i.e., 3500 ppm), which was 6.7°. Further, the most effective SAS was the MgCl2 + CTAB + AOS (i.e., 3500 ppm) solution. Moreover, the best foam was generated via MgCl2 + CTAB + AOS + N2 (i.e., 3500 ppm). Thereafter, the SWAF process yielded an incremental oil recovery of 42% of oil initially in place (OIIP), resulting in a cumulative oil recovery of 92% OIIP. Subsequently, utilizing the CMG-STARS simulator, the experimental coreflood was accurately history matched using the validated SWAF proposed model with a satisfactory error of only 6.7%. Under optimum conditions, it is anticipated that the newly proposed hybrid SWAF EOR-technique is more appealing from an economic and environmental standpoints. This work presents a workflow to mechanistically and experimentally determine the optimum conditions for the SWAF process in carbonates. The study also sheds insight into the mechanisms controlling the SWAF method and promotes designing successful field-scale pilots in carbonate reservoirs.

Abstract As the world transitions to clean energy sources, Underground Hydrogen Storage (UHS) has emerged as a leading solution for large-scale hydrogen storage. While the depleted oil or gas reservoirs are ideal for UHS, the effect of geochemical reactions among injected hydrogen, wellbore, and cement is not documented. This study aims to assess cement and well integrity by examining the geochemical interaction between API cement and hydrogen near the wellbore under varying temperature and pressure conditions. The numerical simulation was carried out to study the geochemical reaction between hydrogen and API class G/H cement minerals using the PHREEQC version 3 simulator. The dissolution reactions of hydrogen with the initial cement components, namely calcium tetra calcium alumino-ferrite (C4AF), tricalcium aluminate (C3A), tricalcium silicate (C3S), and dicalcium silicate (C2S) were modelled at various pressure and temperature conditions. The simulation assumed continuous cement hydration over an infinite time to assess the long-term effects of hydrogen-cement interactions and its impact on cement integrity near the wellbore. Based on this numerical simulation, we found that at 56.2oC, the formation of calcium silicate hydrate(CSH), portlandite, C3AH6, Mackinawite, magnetite, and hydrotalcite. At 95°C, similar minerals were formed with slightly higher amounts of CSH and slightly less portlandite, while others did not exhibit a noticeable difference. At 119°C, it was observed that a noticeable increase in CSH and a noticeable reduction in portlandite amount. Additionally, the formation of ettringite was observed at elevated temperatures. These findings highlight the temperature- dependent changes in mineral composition near the wellbore, which may have implications for the long-term integrity of the cement matrix in hydrogen-affected environments. Based on comprehensive numerical simulation studies, this paper highlights critical insights for a better understanding of hydrogen-cement interactions in the context of underground hydrogen storage, and its impact on the long-term-integrity of wellbores in hydrogen storage application, essential for enhancing the knowledge base for safe and effective implementation of underground hydrogen storage technologies.

Abstract Low Salinity Polymer (LSP) flooding is one of the emerging synergic techniques in enhance oil recovery (EOR). Previous experimental studies showed an exceptional improvement in displacement efficiency, polymer rheology, injectivity, and polymer viscoelasticity. Nevertheless, when it comes to modeling LSP flooding, it is still challenging to develop a mechanistic predictive model that captures polymer-rock-brine interactions. Therefore, this study employs a coupled geochemical-reservoir numerical model to investigate the effect of water chemistry on polymer-brine-rock geochemical interactions during LSP flooding through varying overall salinity as well as the concentrations of monovalent and divalent ions. In this study, the MATLAB Reservoir Simulation Toolbox (MRST) was coupled with a geochemical interface module i.e., pH-Redox-Equilibrium in C programming language (PHREEQC), termed as IPHREEQC. The coupled MRST-IPHREEQC simulator enables simulating the effects on different parameters on polymer viscosity including the Todd-Longstaff mixing model, inaccessible pore volume, permeability reduction, polymer adsorption, salinity, and shear rate. For describing the related geochemistry, the presence of polymer in the aqueous phase was considered by introducing novel solution specie to the Phreeqc database. Using this coupled simulator, several geochemical reactions and parameters can be assessed including rock and injected water compositions, injection schemes, and other polymer characteristics where the focus of this work is on water chemistry. Moreover, different injection schemes were analyzed including low-salinity water, low-salinity polymer injection (1×LSP), and 5-times spiked low-salinity polymer injection (5×LSP) with their related effects on polymer viscosity. The results showed that polymer viscosity during low-salinity polymer flooding is directly affected by calcium (Ca2+) and magnesium (Mg2+) ions and indirectly affected by sulfate ion (SO42−) as a result of polymer-rock-brine interactions on a dolomite rock-forming mineral. Furthermore, the findings showed that monovalent ions such as sodium (Na+) and potassium (K+) have less pronounced effects on the polymer viscosity. However, the release of calcium (Ca2+) and magnesium (Mg2+) ions due to the dissolution of dolomite led to the formation of polymer (acrylic acid, C3H4O2) complexes and consequently, a pronounced decrease in polymer viscosity. In addition, the increase of sulfate ion (SO42−) concentration in the injected LSP solution affects the interactions between the polymer and positively charged aqueous species and leads to less polymer viscosity loss. Additionally, as a de-risking measure for LSP flood designs, estimating the effect of each ion can be highly useful step. The effect of cations is also related to charge ratio (CR), which renders it the key objective to determine the optimum CR ratio at which viscosity loss of LSP flood is avoided or at least minimal. The coupled simulator works as an integrated tool, which is sound, precise, and adaptable with the ability to encapsulate the reactions required for LSP mechanistic modeling. This paper is among the very few, which describe mechanistic geochemical modeling of the low-salinity polymer flooding technique. The coupled simulator provided new insights into understanding the mechanisms controlling LSP flooding. Based on the findings of this work, several successful low salinity-polymer field pilots can be designed.