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International audience; This work presented a study on the chromatographic partitioning of CO2 and impurities present in the injected stream in the CCS context. Laboratory and field observations have already revealed the chromatographic partitioning phenomenon of CO2 and impurities both in the gas and in the aqueous phases. Series of laboratory experiments are modeled using the reactive transport HYTEC. Numerical results confirm the laboratory observations and show differential breakthrough of injected gases. A series of experiments on CO2 and H2S mixture with different H2S concentration is modeled. Numerical results of HYTEC are successfully compared with the results given by CMG-GEM and with experimental data. Another series of dynamic displacement-solubility experiments is modeled to study the chromatographic gas partitioning depending on a type of impurity such as H2S, CH4, N2, SO2. O2, and Ar. Numerical results show that the physics can be modeled both qualitatively and quantitatively. 1. Solubility of the impurity in the injected stream regarding to that of CO2 is a key factor. The less soluble the impurity gas is, the earlier and higher breakthrough should be expected. 2. Classification of impurity gases can be proposed. For example, in the decreasing order of their solubility (13.5 MPa, 61°C, 118950 ppm): SO2 > H2S > CO2 > CH4 > Ar > O2 > N2. 3. Using accurate models of reactive transport, solubility, phase equilibrium and thermodynamic properties of non-ideal mixtures allows reproducing of the chromatographic partitioning: breakthrough time of gases, gas concentration, and front propagation. Chromatographic partitioning was studied at reservoir scale by modeling two scenarios of impure CO2 injection over 30 years: 95%CO2+4%N2+1%O2 and 95%CO2+5%SO2. When injecting impurities, the chromatographic partitioning can be observed inside the gas plume and in the aqueous solution. Modeling injection of 95%CO2+4%N2+1%O2 demonstrated potential usage of noble gases for monitoring and proved the previous laboratory results. The plume composition strongly depends on a type of the co-injected gas. Moreover, a type of impurity and its concentration change the density of gas current and the density of the formation water with dissolved components. Both densities in the case of 95%CO2+5%SO2 injection are overall higher than those in the 95%CO2+4%N2+1%O2 model. This impacts on the buoyancy forces, hence on the distance, velocity and shape of the plume. Since dissolved impurities contribute to the liquid density, it can then accelerate or slow convective dissolution. Heterogeneous gas composition induces density driven motion that can be especially important in case of heavy compounds such as SO2.

International audience

International audience; HYTEC is a reactive transport code developed at MINES ParisTech since 1996. Over the last few years, a new two-­‐phase flow module was embedded in HYTEC with emphasis on modularity and flexibility. Although based on the phase formulation of the flow problem, the method allows for the precise description of complex gases (multicomponent, non-­‐ ideal), their thermodynamic and hydrodynamic behaviors, and the coupling with water-­‐ rock interaction. The developed algorithm relies on several modules: the compressible multiphase flow problem (based on the fully implicit method), a complex thermodynamic operator (built on analytical modeling of equations of state, fluid property models and their derivatives), and a sequential iterative resolution of the reactive transport. The global coupling approach is organized around the sequential iterative call for two blocks: on the one hand two-­‐phase flow, gaseous transport and thermodynamic operator, on the other hand chemistry and aqueous and gaseous transport. The impact of phase consumption (gas dissolution, exsolution of dissolved gases) on hydrodynamics is explicitly described. Several applications are proposed to illustrate the behavior of the code. E.g., the simulation of an impure CO2 injection in a homogeneous fully saturated reservoir (Figure 1) performed by Irina Sin during her PhD (Sin, 2015) displays some chromatographic effects due to differences in gas solubility. The gas current is formed by diffusion, advection-­‐dominated flow, and by density-­‐driven forces. In addition, the gas plume is enriched with less soluble gases (N2, O2 and H2O) at the two-­‐phase front (Figure 2); oppositely, more soluble SO2 is depleted (Figure 3). Other applications can lay the basis for benchmarking exercises. Sin (2015) " Numerical simulation of compressible two-­‐phase flow and reactive transport in porous media – Applications to the study of CO2 storage and natural gas reservoir " , Ph.D. MINES ParisTech. Figure 1 : 2D radial injection of CO2 with air impurity (4% N2 and 1% O2), liquid density after 10 y.

Human activity in the subsurface has rapidly been expanding and diversifying (waste disposal, new mining technologies, high-frequency storage of energy), while the public and regulatory expectations keep growing. The assessment of each step of underground operations requires careful safety and environmental impact evaluations. They rely on elaborate simulators and multiphysics modeling. With its process-based approach, reactive transport simulation provides an effective way to understand and predict the behavior of such complex systems at different time and spatial scale.This work aims at incorporating a compressible multiphase flow into conventional reactive transport framework by an operator splitting approach. A multiphase flow module is developed in the HYTEC reactive transport software. A new approach is then developed to fully couple multiphase multicomponent compressible flow, the complex thermodynamic description of the fluid properties, with existing reactive transport codes. The method is implemented in HYTEC. Some validation is provided, before application to the simulation of underground storage of CO2 and associated impurities., Les activités humaines dans la subsurface se développent rapidement (stockage de déchets,nouvelles techniques minières, stockage à haute fréquence de l’énergie), alors que dans le même temps les attentes du public et des autorités s’intensifient. L’évaluation de chaque étape de ces opérations souterraines repose sur des études détaillées de la sûreté et des impacts environnementaux.Elles reposent sur des simulateurs élaborés et sur de la modélisation multiphysique. Avec leur approche orientée processus, les simulations en transport réactifs proposent une méthode efficace pour comprendre et prévoir le comportement de ces systèmes complexes, à différentes échelles de temps et d’espace.Le but de ce travail est d’intégrer la résolution de l’écoulement diphasique compressible dans le cadre de codes de transport réactifs à l’aide d’une méthode de séparation d’opérateurs. Un module multiphasique a été créé dans le code de transport réactif HYTEC. Une nouvelle approche a ensuite été développée pour coupler écoulement multicomposant multiphasique compressible, description de propriétés thermo-dynamiques complexes pour les fluides, avec des codes de transport réactif. La méthode a été intégrée dans HYTEC. Des cas de validation sont proposés, puis des exemples d’application pour la simulation du stockage souterrain de CO2 et des impuretés associées.

International audience

International audience

International audience; During CO2 injection, the near-well composite zones undergo geochemical, mechanical perturbations by gas stream. The numerical modelling of these coupled processes aims at complementing laboratory experiments to verify the integrity of CO2 storage.This study presents the development of a two-phase flow module in the reactive transport software HYTEC. The former is resolved on a Voronoi-based finite volume discretization, using a water pressure/gas saturation formalism and a fully implicit method. The module was successfully compared against a self-similar solution and tested on the effects of gravity and absolute/relative permeability heterogeneity.The coupling between the developed two-phase flow module and HYTEC’s reactive transport methods is sequential. The thermodynamic gas properties are calculated using the equations of state; the liquid and gas transports are resolved separately. The chemical equilibrium is made by software CHESS. One of the main problems is to feed volume (gas and water) changes from the chemistry-transport (and phase equilibrium) resolution back to the flow module. We present test case results of coupling code.

Les milieux composites proches des puits d'injection de CO2 présentent de fortes hétérogénéités spatiales ainsi que la réactivité importante des processus physico-chimiques couplés. Cette hétérogénéité a des impacts sur l'injectivité et sur l'intégrité des stockages. L'interprétation de pilote et d'expérience peut être utilement complétée par la modélisation numérique de transport réactif pour quantifier certains phénomènes difficiles à mesurer et transposer les résultats à l'échelle du stockage. L'étude présentée ici montre le développement d'un module d'écoulement biphasique dans le logiciel de transport réactif HYTEC. La résolution repose sur un formalisme pression d'eau/saturation de gaz, complètement implicite, sur une discrétisation volumes finis sur des éléments de Voronoï. La méthode a été testée vis-à-vis d'une solution auto-similaire. Les effets de l'hétérogénéité (variations spatiales de perméabilité absolue/relative et de porosité) sont observés sur un cas-test de référence. La suite de l'étude portera sur le couplage du module biphasique avec les méthodes de transport et de chimie du code. L'impact de l'hétérogénéité sur l'évolution géochimique, et la rétroaction de la chimie sur le milieu seront étudiés. Une application sera réalisée sur une expérience effectuée à l'Université de Lorraine.