In this work, we use molecular simulations to determine the structural and physical properties of the organic matter present in type II shales in the middle of the oil generation window. The construction of molecular models of organic matter constrained by experimental data is discussed. Using a realistic molecular model of organic matter, we generate, by molecular dynamics simulations, structures that mimic bulk organic matter under typical reservoir conditions. Consistent results on density, diffusion, and specific adsorption are found between simulated and experimental data. These structures enable us to provide information on the fluid distribution within the organic matter, the pore size distributions, the isothermal compressibility, and the dynamic of the fluids within the kerogen matrix. This study shows that a consistent description at the molecular level combined with molecular simulations can be useful, in complement of experiments, to investigate the organic matter present in shales.

International audienceDuring the past decade, gas recovered from shale reservoirs has jumped from 2 to 40% of natural gas production in the United States. However, in response to the drop of gas prices, the oil and gas industry has set its sights on the oil-prone shale plays, potentially more lucrative. This shift from dry to condensate-rich gas has raised the need for a better understanding of the transport of hydrocarbon mixtures through organic-rich shale reservoirs. At the micrometer scale, hydrocarbons in shales are mostly located in amorphous microporous nodules of organic matter, the so-called kerogen, dispersed in an heterogeneous mineral matrix. In such multiscale materials, a wide range of physical mechanisms might affect the composition of the recovered hydrocarbon mixtures. More specifically, kerogen nodules are likely to act as selective barriers due to their amorphous microporous structure. In this work, we study the transport of hydrocarbon mixtures through kerogen by means of molecular simulations. We performed molecular dynamics simulations of hydrocarbons permeating through a molecular model representative of oil-prone type II kerogen. Our results show that the permeation mechanisms through this type of material is purely diffusive. Consequently, we have computed the Onsager's species-specific transport coefficients of a typical condensate-rich gas mixture within kerogen. Interestingly, we have observed that the transport coefficients matrix can be reasonably approximated by its diagonal terms, the so-called Onsager's autocorrelation coefficients. Inspired by the classical Rouse model of polymer dynamics and surface diffusion theory, we propose a simple scaling law to predict the transport coefficient of linear alkanes in the mixture. In good agreement with our simulations results, the Onsager's autocorrelation coefficients scale linearly with the adsorption loading and inversely with the alkane chain length. We believe our results and predictions are applicable to other materials, such as carbon-based synthetic microporous membranes, with structural properties close to that of kerogen

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In this article we investigate the importance of mass transfer effects in the effective acoustic properties of diluted bubbly liquids. The classical theory for wave propagation in bubbly liquids for pure gas bubbles is extended to capture the influence of mass transfer on the effective phase speed and attenuation of the system. The vaporization flux is shown to be important for systems close to saturation conditions and at low frequencies. We derive a general expression for the transfer function that relates bubble radius and pressure changes, solving the linear version of the conservation equations inside, outside and at the bubble interface. Simplified expressions for various limiting situations are derived in order to get further insight about the validity of the common assumptions typically applied in bubble dynamic models. The relevance of the vapour content, the mass transfer flux across the interface and the effect of variations of the bubble interface temperature is discussed in terms of characteristic non-dimensional numbers. Finally we derive the various conditions that must be satisfied in order to reach the low-frequency limit solutions where the phase speed no longer depends on the forcing frequency.

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...

The wax appearance temperature as well as the liquid vapor phase boundary were measured on two condensate gases from a high-temperature-high-pressure field in the North Sea. Measurements were performed up to 45 MPa in the temperature range from 293 to 423 K. The experimental temperatures of wax appearance were then compared to the prediction of a model previously developed for synthetic light gas-heavy n-paraffins systems and adapted here to the representation of live oils.