HYTEC results of the MoMas reactive transport benchmark

International audienceA specific benchmark has been developed by the french research group MoMas in order to improve numerical solution methods applied by reactive transport models, i.e. codes which couple hydrodynamic flow and mass transport in porous media with geochemical reactions. The HYTEC model has been applied to this benchmark exercise and this paper summarizes some of the principal results. HYTEC is a general-purpose code, applied by industrials and research groups to a wide variety of domains, including soil pollution, nuclear waste storage, cement degradation, water purification systems, storage of CO2 and valorization of stabilized wastes. The code has been applied to the benchmark test-cases without any specific modification. Apart from the benchmark imposed output, additional information is provided to highlight the behavior of HYTEC specifically and the simulation results in particular

Operator splitting-based reactive transport models in strong feedback of porosity change: the contribution of analytical solutions for accuracy validation and estimator improvement

Journal of Contaminant Hydrology, Special issue : Frontiers in Reactive Transport: Microbial Dynamics nad Redox Zonation in the Subsurface Edited by T.D. Scheibe and C.I. SteefelInternational audienceReactive transport is a highly non-linear problem requiring the most efficient algorithms to rapidly reach an accurate solution. The non-linearities are increased and the resolution is even more demanding and CPU-intensive when considering feedback of dissolution or precipitation reactions on hydrodynamic flow and transport, commonly referred to as the variable porosity case. This is particularly true near clogging, which leads to very stiff systems and therefore small time-steps. The operator-splitting approach often cited is a widely use method to solve these problems: it consists in solving sequentially the transport then the chemistry part of the problem. Operator-splitting appears to be an accurate approach, provided that the solution is iteratively improved at each time-step. The paper details analytical solutions and test-cases for this class of problems. They demonstrate that iterative improvement is then compulsory. They also helped develop an improved estimator/corrector method which allows to reach convergence faster and to reduce stiffness. The efficiency improvement is significant as illustrated by an example of carbonation of a cement paste, a well-known problem that leads to complete clogging of the interface layer

Influence des processus géochimiques sur le transport en milieu poreux -- application au colmatage de barrières de confinement potentielles dans un stockage en formation géologique

The study aims at exploring the feedbacks between geochemical reactions and flow and transport processes before their integration in reactive transport codes. Several applications are tested in the context of long term evolution of confining barriers of geological disposals.L'objectif de l'étude est d'explorer les rétroactions entre réactions géochimiques et processus hydrodynamiques d'écoulement et de transport en vue de leur intégration dans des codes de simulations de transport réactif. Des applications sont testées dans le contexte de l'évolution à long terme de barrières de confinement dans un stockage géologique

Heterogeneous modeling of the uranium in situ recovery: Kinetic versus solubility control

The uranium in situ recovery (ISR) is a mining technique, which involves injecting an acid or alkaline solution, into the deposit to selectively dissolve uranium. The solution enriched in uranium is pumped out and processed. Once the uranium is removed, reagent is added to the solution, which is then reinjected. This method is particularly suited to deep and low-grade deposits located in confined aquifers. In this work, we focus on the case of the Tortkuduk deposit, in Kazakhstan, where the reagent is sulfuric acid. The main objective of this work is to understand how the uranium production can be increased while the sulfuric acid consumption is maintained as low as possible. It requires devising and validating an ISR phenomenological model, using all available tools: experiments, production data and numerical simulation, from 1D homogeneous to 3D heterogeneous models

Reactive Transport Modelling of CO2 Sequestration in Saline Aquifers

International audienceGeological sequestration of CO2 in deep saline aquifers may offer numerous opportunities for the mitigation of greenhouse gas emissions. In order to ensure good containment, a correct understanding of the evolution of such systems after a massive injection of CO2 is compulsory. For this purpose, coupled reactive transport modelling can provide useful information, by simulating chemical reactions likely to occur in the system coupled to reactive transport, at large time and space scales.This study aimed at investigating the possible benefits of reactive transport modelling in the context of CO2 sequestration. Two deep saline aquifers have been chosen to test the performance and limitationsof the codes: the carbonated aquifer of the Dogger (Paris Basin) and the sandstone aquifer of the Bunter (North Sea). The aquifers, with contrasting behaviours, have been chosen to illustrate the main expected phenomena: CO2 dissolution in the carbonated aquifer, carbonate mineral precipitation in the sandstone aquifer. The simulations highlight the performance of the reactive transport codes, particularly the possibility to represent in detail a source (or sink) term with the dissolution of the CO2 bubble (or the precipitation of carbonated minerals), coupled to the transport of the dissolved CO2. Furthermore, flux assessment at various points of the system illustrates the storage capacity of the systems. However, several shortages have been identified: a lack of data on the aquifers and on the reactivity of CO2 under sequestration conditions. Finally, developments are advisable to better estimate the transport, dissolution and reactivity of the supercritical CO2: This involves a two-phase coupled reactive transport code, and a coupling with the exchange between phases

Mechanisms of gas migration in flooding post-mining context

International audienceThe French national institute for industrial environment and risks (ineriS), in a support mission to state services and as a partner of the european project FLOMineT, is studying gas migration during and after mine flooding. in situ flow measurements and laboratory records acquired with an experimental device are being used to study gas transfer and to characterize the influence of hydrostatic pressure on methane release from coal. in parallel, several models are in development using the HYTec code to describe mine methane migration. The combined use of numerical and experimental approaches will make it possible to improve risk prevention concerning surface gas emission above the old mines

Interaction eau-roche-CO2 en contexte de fuite contrôlée de CO2: apport du monitoring géochimique et isotopique lors d'un cas réel d'injection de CO2

Cette étude montre, dans un cas réel d'injection de CO2, comment une approche multi- isotopique (B, Li, S, O, Sr) combinée aux données chimiques permet (i) de tracer indirectement la réactivité et présence du CO2, (ii) de contraindre et comprendre précisément les interactions eau-roche-CO2 et les réponses isotopiques. L'originalité de ce travail consiste à utiliser des outils isotopiques développés dans les géosciences pour les appliquer à ce contexte particulier. L'idée majeure est d'utiliser ces outils comme traceurs des interactions eau-roche-CO2 afin de détecter toute anomalie de fuites de CO2 non décelables par les autres moyens de monitoring existant

The influence of spatial variability on 2D reactive transport simulations

International audienceIn reactive transport simulations, the effects of the spatial variability of geological media are generally neglected. The impact of this variability is systematically examined here in 2D simulations, with a simple geometry and chemistry with a positive feedback: increase of porosity and of permeability during calcite dissolution. The results highlight the leading role in these conditions of: (i) the correlation length of porosity and of permeability; and (ii) the kinematic dispersivity, whose effects are dominant compared to those of variance and reaction kinetics. The impact of stochastic variability (between several randomdraws) is also significant, as it is of the same order of magnitude as the impact of the range and dispersivity

Both experimental study and numerical modelling of the effect of temperature gradient on CO2 injection

CO2 injection and underground storage obviously requires dealing with temperature differences between the injection well and the reservoir. Temperature enhances both species transport and reactions kinetics, while CO2 solubility also greatly decreases with temperature. This point could be of great importance especially in wellbore surroundings, although it has not been the subject of devoted studies up to now. To assess this issue, an experimental set up, COTAGES, has been designed (Fig.1). It consists in a 0.72m-long cylindrical autoclave (the diameter is 2.1cm) that can be filled with 12 fiberglass/teflon packets containing 12.5 grams of mineral grains and a pre-equilibrated saline aqueous solution. When loaded, one end of the autoclave is heaten up and maintained at 100°C. After having reached a steady-state, the other end is around 30°C. Finally, CO2 is injected in the cold zone (100 bars) and, from this moment, the experiment lasts 1 month while both pressure and temperatures (3 zones) are being monitored. The first results show the same general trend for both a reservoir rock such as oolitic limestone (Lavoux, France) and clay minerals such as COx argillite (Lundin, France). In these two experiments, a global mass loss is observed for all the packets except for those comprised between 75 and 95°C. There, a mass gain is noted and is remarkably important in the case of clay (greater than 11.5%). The greater losses are recorded around 65-70°C and are also of greater importance for COx clay (up to 10.0%). During the whole experiments, quite important variations of the total pressure are observed. Even if they are partly related to CO2 dissolution into water and to temperature variations (due to regulation), they shall also depend on involved chemical reactions. Indeed, after injection, pressure drastically decreases (up to 50 bar less). Since CO2 solubility is higher in the cold zone (more than 4 times), the aqueous solution gets more acidic there. It leads to a more important carbonates dissolution, thus to increases of CO2 fugacity and consequently of the global pressure. Furthermore, the calcium content tends to be greater in this cold-dissolution zone then Ca diffuses towards the hotter zone locally and it implies calcite precipitation. As evidence of this phenomenon, plugs, related to massive calcite precipitation, are observed in these regions and newly crystallized calcite can be seen on SEM images. In order to clearly understand the reasons of the observed behaviour, numerical computations performed with the reaction-transport code HYTEC have to be run. Several scenarios can thus be simulated to check various assumptions. Firstly, different initial repartitions of the CO2 can be tested: in some kind of reservoir in the cold/injection zone or everywhere in the autoclave (due to high initial pressure gradient). Secondly, the competition between the implied processes, their respective kinetics and their temperature dependance can be assessed too: thermodynamics and/or kinetics of chemical reactions and transport kinetics (diffusion). Modeling becomes then of great help to interpret the experimental results and even to better design the evolution of the experimental set-up

Equivalent block transmissivity in an irregular 2D polygonal grid for one-phase flow: a sensitivity analysis

International audienceUpscaling is needed to transform the representation of non additive space-dependent variables, such as permeability, from the fine grid of geostatistical simulations (to simulate small scale spatial variability) to the coarser, generally irregular grids for hydrodynamic transport codes. A new renormalisation method is proposed, based on the geometric properties of a Voronoï grid. It is compared to other classic methods by a sensitivity analysis (grid, range and sill of the variogram, random realisation of a simulation); the criterion is the flux of a tracer at the outlet. The effect of the upscaling technique on the results appears to be of second order compared to the spatial discretisation, the choice of variogram, and the realisation