Molecular Dynamics as a Tool to Deal with Thermogravitation

Abstract: A precise description of the initial state of a petroleum reservoir is crucial to optimize its development plan. This relies on an accurate modeling of the spatial distribution of the fluid components within the reservoir which is mainly influenced by gravitational segregation and thermo-diffusion phenomena (thermogravitation). An alternative to the classical thermodynamic modelling to provide further information on thermogravitation without the need of any EoS or any correlation to describe transport properties is to use Non-Equilibrium Molecular Dynamics (NEMD) simulations on systems representing an idealized 1D reservoir fluid column. We will show how such a molecular based approach can shed light on some the underlying physical mechanism (evolution/stability) of the thermo-gravitational process in idealized situations. In particular, it will be shown, on a n-alkane mixture and a acid gas mixture, that the thermodiffusion effect can affects the vertical distribution of the different compounds as much as segregation with the same characteristic time and can even lead to an unstable (i.e. convective) situation in a CO2 rich reservoir.