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Injection of foams can be used to optimize different gas injection processes such as CCUS (Carbon Capture Use & Storage) and possibly to boost oil recovery kinetics in heterogenous or naturally fractured reservoirs (Enick R.M. 2012). In this case, foams, which are more viscous and dense than gases, aim at limiting early gas breakthrough during field operation by improving the sweeping efficiency of reservoirs and by blocking the most permeable areas of the latters (A. Al Sumaiti 2017, Chabert M. and D'Souza D. 2016). A large part of the world oil reservoirs that have already been operated by primary and secondary recovery methods are carbonate reservoirs and are mostly located in the Middle East (Talebian S.H. 2014). In these reservoirs, which are often operated by CO2 injection, the adsorption of surfactants on positively charged carbonates may be a major hindrance to foam injection (Pownall 1989, Cui L. and Ma K. 2014). That is why, cationic surfactants have been developed for these CO2 foam applications (Chen Y. 2016). However, these cationics are often hardly soluble at pH>6 (Jian G. 2019) and/or not industrially avalaible (Cui et Dubos 2018). For this study, we selected three different cationic surfactants. Using automated robotic platforms, we explored a large range of surfactant combination (combining each cationic surfactant with a whole co-surfactant portfolio) at high temperature and in a hard concentrated brine (120g/LTDS, [Ca2+]= 8100ppm). We show that adding co-surfactants to each of these cationics boosts their foaming properties in porous media as well as their solubility at high pH (pH=8) while maintaining low levels of adsorption on carbonates. While a high shear rate is required for cationic surfactants to generate foam in sandpacks, formulations combining cationics and co-surfactants form foams at much lower shear rates. Moreover, the fact that these formulations are soluble at pH=8 means that, on field, the water would no longer need to be acidified at the wellhead to solubilize the surfactant blend. Thus, pipe corrosion induced by the flow of acidified solutions in the surface facilities is prevented. Lastly, all the molecules that are tested in this study are industrially available.

The understanding of structural and mechanical properties of granular assemblies remains an open issue. The numerical modeling of granular media, using the Molecular Dynamic approach, brings some answers to critical problems. At first, we are studying the effects of mixture parameters on the degree of order and on the stress distribution in these arrangements of grains. Next, we are interested in the acoustic properties of these media, which are very nonlinear in comparison to continuous elastic solids; ours simulations serve to clarify the deficiencies of Effective Medium Theory, which only partially account for the dependency of elastic moduli with pressure. We show that relaxation of grains, following an infinitesimal deformation is an essential component of the shear modulus. There is clearly a need for an alternative formulation and the traditional elasto-plastic approach is faced with new theories. If the numerical simulations led in this study, which measure the response function of granular media (stress field generated by a point force), show an elastic scaling, it also accounts for important relaxation process. The deformation mechanisms of granular materials were also study by simulating bixial compression tests, which reproduce qualitatively well the classical mechanicals data (stress peak, compaction/dilatancy transition), and also localization of the deformation; while at low pressure, grains rotations accommodate the deformation, at high pressure, the mobilization of friction is more pronounced. Finally, we propose a probabilistic model of damage of granular rocks, which predicts a dependency of damage both with the cementation heterogeneity and with the sample size. These predictions are confirmed by simulations, which also highlight two successive damage behaviors, diffuse at first and then concentrated in clusters., La compréhension des propriétés structurales et mécaniques des assemblages granulaires reste un problème ouvert. La modélisation numérique de ces milieux par Dynamique Moléculaire permet de répondre à certaines interrogations. Tout d'abord, nous étudions les effets des paramètres de mélange sur le degré d'ordre et la distribution des contraintes dans ces arrangements de grains. Ensuite, nous nous intéressons aux propriétés acoustiques de ces milieux, très nonlinéaires comparées aux solides élastiques continus; nos simulations servent à clarifier les déficiences de la Théorie de Milieu Effectif, qui rend partiellement compte de la dépendance en pression des modules élastiques, et elles montrent que la relaxation des grains après une déformation infinitésimale est une composante essentielle du module de cisaillement. Il y a donc un besoin pour une formulation alternative et l'approche traditionnelle élasto-plastique a été remise en cause par des nouveaux modèles. Si l'expérience numérique menée de mesure de la fonction réponse (champ de contrainte généré par une force ponctuelle) montre une remise à l'échelle élastique, elle rend également compte de phénomènes importants de relaxation. Les mécanismes de déformation des matériaux granulaires ont aussi été étudiés en simulant des essais biaxiaux; ils reproduisent qualitativement les données mécaniques classiques (pic de contrainte, transition compaction/dilatance) et aussi la localisation de la déformation; à faible pression, les rotations de grains accommodent la déformation tandis qu'à forte pression, la mobilisation du frottement est plus marquée. Enfin, nous proposons un modèle probabilistique d'endommagement de roches granulaires qui prédit une dépendance de l'endommagement avec à la fois l'hétérogénéité de cimentation et la taille d'échantillon. Ces prédictions sont confirmées par des simulations qui permettent également de mettre en évidence deux régimes d'endommagement successifs, diffus puis concentré en amas.

[Notes_IRSTEA]WR011385 [Departement_IRSTEA]Eaux [TR1_IRSTEA]ARCEAU; International audience; The recent advances in 3-D imaging of porous structures have generated a tremendous interest in the simulation of complex single and two-phase flows. Lattice-Boltzmann (LB) schemes present a powerful tool to solve the flow field directly from the binarized 3-D images. However, as viscosity often plays an important role, the LB scheme should correctly treat viscosity effects. This is the case using a LB scheme with two relaxation times (TRT) unlike the broadly used, the single-relaxation rate, BGK, where the velocity of the modeled fluid does not vary as the inverse of the viscosity applying the bounce-back (no-slip) boundary rule. The aim of this work is to apply the LB-TRT approach to different types of porous media (straight channels, 2-D model porous media, sandstone) to solve for the flow field and to evaluate the approach in terms of parameter dependence, error and convergence time on the basis of permeability. We show that the variation of permeability with the free relaxation parameter L of the TRT scheme depends on the heterogeneity of the sample and on the numerical resolution. The convergence time depends on the applied viscosity and the parameter standing for the speed of sound, thus the computation time can be reduced by choosing appropriate values of those parameters. Two approaches to calculate permeability (Darcy’s law and viscous energy dissipation) are proposed and investigated. We recommend to use Darcy’s law, as dependence on L is less important. Periodic (in the presence of a driving body force) and pressure boundary conditions are evaluated in terms of the results.

Colloque avec actes et comité de lecture. Internationale.; International audience; On réalise sur des échantillons cylindriques des essais drainés en appliquant divers chemins de chargement, caractérisés par le rapport des contraintes radiale et axiale (K). Le mode d’endommagement et son influence sur la perméabilité dépendent surtout de K, mais dans des régimes intermédiaires, les hétérogénéités jouent un rôle majeur. Nous proposons une normalisation des données expérimentales qui permet de définir sans autre ajustement l’enveloppe de rupture dans le plan des contraintes.

Colloque avec actes et comité de lecture. Internationale.; International audience; La méthode de détermination des champs de déformation à partir de corrélation d’images a été appliquée à toutes les échelles pour des échantillons centimétriques de grès et de carbonates observés sous chargement en microscopie optique et électronique à balayage. On peut ainsi observer les diverses étapes du développement de localisations et des mécanismes parfois antagonistes affectant la perméabilité de l’échantillon, comme la diminution de porosité et l’ouverture de microsfissures.