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.

Understanding the atmosphere's composition during the Archean eon is a fundamental issue to unravel ancient environmental conditions. We show from the analysis of nitrogen and argon isotopes in fluid inclusions trapped in 3.0-3.5 Ga hydrothermal quartz that the PN2 of the Archean atmosphere was lower than 1.1 bar, possibly as low as 0.5 bar, and had a nitrogen isotopic composition comparable to the present-day one. These results imply that dinitrogen did not play a significant role in the thermal budget of the ancient Earth and that the Archean PCO2 was probably lower than 0.7 bar

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