15Shales are ubiquitous rocks in sedimentary basins, where their low permeability makes them 16 efficient seals for oil and gas reservoirs and underground waste storage repositories (waste 17 waters, CO2, nuclear fuels). Moreover, when they contain organic matter, they form source 18 rocks for hydrocarbons that may escape towards a more porous reservoir during burial, a 19 process referred to as primary migration. And when the hydrocarbons cannot escape, these 20 rocks can be exploited as oil or shale gas reservoirs. While the presence of fractures at the 21 outcrop scale has been described, the existence of fractures at smaller scales, their link with

Re´sume´-Mode´lisation mole´culaire de l'adsorption dans les solides microporeux -L'existence de logiciels industriels, la baisse du couˆt du calcul et la disponibilite´de champs de force e´prouve´s rendent la simulation mole´culaire de plus en plus attrayante pour les applications du domaine du ge´nie chimique. Nous pre´sentons ici plusieurs applications des techniques de simulation de Monte-Carlo, applique´es a`l'adsorption de fluides dans des solides microporeux (pores < 2 nm) comme les ze´olithes et des structures microporeuses a`base de carbone. L'adsorption a e´teḿ ode´lise´e par simulation dans l'ensemble Grand Canonique graˆce au logiciel MedeA Ò -GIBBS, en utilisant des grilles tridimensionnelles de valeurs pre´-calcule´es de l'e´nergie pour optimiser le temps calcul. MedeA Ò -GIBBS a aussi e´te´utilise´pour obtenir les potentiels chimiques ou les fugacite´s dans les phases fluides libres au moyen de l'ensemble Canonique (NVT) ou de l'ensemble isotherme-isobare (NPT). Les re´sultats de simulation ont e´te´compare´s avec des donne´es expe´rimentales d'isothermes d'adsorption de corps purs (gaz hydrocarbures, eau, aromatiques, e´thanethiol) dans plusieurs ze´olithes et a`plusieurs tempe´ratures. La coadsorption de me´langes (me´thane-e´thane, n-hexane-benze`ne) dans les ze´olithes a aussi e´te´e´tudie´e. Par exemple, l'inversion de se´lectivite´n-hexane/benze`ne entre la silicalite et les Na-faujasites est bien pre´dite avec des champs de force publie´s, et permettent de comprendre les me´canismes sousjacents. De meˆme, les isothermes d'adsorption des hydrocarbures le´gers et d'un mercaptan (e´thyl-thiol) sont bien de´crite. En ce qui concerne les adsorbants organiques (ke´roge`ne et charbons matures), des mode`les mole´culaires moyens ont e´te´construits en rendant compte des principaux traits connus de la structure chimique de ces mate´riaux. Par une simple relaxation ab ase de dynamique mole´culaire, nous avons pu obtenir des densite´s moyennes en bon accord avec les donne´es expe´rimentales disponibles, ce qui est tre`s encourageant. Nous avons aussi de´termine´les courbes isothermes d'exce`s d'adsorption en bon accord qualitatif avec celles re´cemment mesure´es sur des e´chantillons de charbon ou d'argiles en l'absence d'eau. Bien que pre´liminaires, ces re´sultats illustrent la puissance et la ge´ne´ralite´de la mode´lisation mole´culaire en vue de la compre´hension de syste`mes complexes dans des conditions ou`l'expe´rimentation est difficile.Abstract -Molecular Simulation of Adsorption in Microporous Materials -The development of industrial software, the decreasing cost of computing time, and the availability of well-tested Oil & Gas Science and Technology -Rev. IFP Energies nouvelles, Vol. 68 (2013), No. 6, pp. 977-994 Copyright Ó 2013, IFP Energies nouvelles DOI: 10.2516 forcefields make molecular simulation increasingly attractive for chemical engineers. We present here several applications of Monte-Carlo simulation techniques, applied to the adsorption of fluids in microporous solids such as...

International audienceThe reservoir response of unmineable coal seams to primary and enhanced natural gas recovery is strongly affected by gas sorption and the swelling properties of the coal reservoir rock. In-depth understanding of the process of gas sorption/desorption in the coal matrix, induced deformation and measurement of relevant physical parameters are critical for predictive reservoir management. Models used in industry practice are based on swelling strains measured in “free” swelling coal or on empirical correlations between strain and adsorption, and predict permeability changes based on changes of porosity or stress calculated assuming an analogy with thermoelasticity. However, not only coal seams are subjected to in-situ stresses and geometrical boundary conditions but also sorption and strain are strongly coupled. Representative experiments and a truly coupled model for coal seams are needed in challenging applications. We present a set of triaxial testing measurements on 38 mm diameter fractured sub-bituminous/bituminous coal cores exposed to CO2. Testing includes the measurement of fluid uptake, adsorption-induced strains and stresses, and the impact on simultaneously measured permeability. Noteworthy, we measured increases in effective stress of up to 29 MPa when injecting CO2 at 5 MPa and preventing the coal core to swell. The results are analyzed with a poromechanical model in which coal matrix microporosity and adsorption-induced phenomena are embedded into a fractured reservoir rock with transverse isotropic properties. The adsorptive–mechanical coupling in the coal matrix is integrated through an adsorption stress function and fractured coal permeability is estimated as a function of Terzaghi's effective stresses (parallel and perpendicular to the bedding plane). The experimental results and model predictions help identify the characteristic response of coal microporosity and cleat macroporosity on the poromechanical response of coal cores, and suggest that order of magnitude changes of reservoir permeability observed in the field are linked to sorption-induced change on Terzaghi's effective horizontal stress under laterally constrained displacement condition. Together, the modeling and experimental characterization offer unprecedented insights into the mechanics of coal

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