Technological advances in oil & gas industry have made possible the recovery of hydrocarbons from shale and tight reservoirs – which were previously inaccessible due to the nanometric nature of their pores. This brought the imperative need to develop tools that improve the description of the properties of fluids under confinement, which involves many challenges due to the peculiar characteristics that arise from the interactions between the fluid and the confining medium. Furthermore, a good description of the thermodynamic and transport properties of fluids inside hydrocarbon reservoirs is fundamental to perform estimations of reservoir production forecast and economic analysis [1]. In this work, we carried out molecular dynamics simulations of complex multicomponent mixtures confined within calcite slit nanopores to evaluate the wettability and adsorption phenomena under different reservoir conditions.
Wettability plays a fundamental role in carbon sequestration processes, but there are still gaps on the understanding of the effects that different reservoirs conditions have on this phenomenon. To analyze the wettability inside calcite nanopores, we performed molecular dynamics simulations of mixtures of CO2 and liquid water, and CO2 and brine confined by calcite for different conditions of the system. Understanding the mechanisms involved in water wettability inside nanopores is of high relevance as CO2 trapping has shown to largely increase in strongly water-wet pores [2]. In addition, we studied the adsorption of mixtures of CO2 and different alkanes within calcite slit nanopores through molecular dynamics simulations for a set of different temperatures, compositions, and pore sizes. We were able to observe that a higher concentration of CO2 inside the nanopore leads to a higher fraction of CO2 being adsorbed to the surface of the calcite, regardless of the size of the alkane contained in the system. Another aspect observed is that alkanes with a longer chain tend to adsorb parallel to the surface of the calcite, which has an impact on the available area for CO2 adsorption on the calcite surface. Furthermore, we also observed that the temperature has a large impact on the local compositions next to the calcite surface, especially for high densities inside the pore, as we have observed much higher amounts of CO2 at the adsorbate layer at low temperatures than at high temperatures. Lastly, we evaluated the impact of the presence of water within the nanopore in the adsorption selectivity of CO2 over alkanes.
References:
[1] Wang, S, Feng, Q, Javadpour, F, Xia, T, Li, Z, Oil adsorption in shale nanopores and its effect on recoverable oil-in-place. I. J. Coal Geol., 147-148, 9-24 (2015).
[2] Iglauer, S, Pentland, C H, Busch, A, CO2 wettability of seal and reservoir rocks and the implications for carbon geo-sequestration. Water Resour. Res., 51, 729-774 (2015).
Advances in molecular simulation , Interfacial and confined phenomena
