Although our understanding of the full range of pore features developed in various geological settings continues to advance, we expect that the thermo-physical behavior of complex supercritical C-O-H fluids in nano-confined geometries will exhibit differences compared to bulk fluids. There is general agreement that the collective structure and properties of bulk fluids such a CH4, C2H6 and CO2 are altered by solid substrates, confinement between two mineral surfaces or in narrow pores due to the interplay of the intrinsic length scales of the fluid and the length scale of confinement. The resulting interfacial areas (fluid-fluid, and mineral-fluid) are relatively large within the pore volume and therefore control chemical and transport behavior in shale and other earth materials containing nanopore regimes. The combined effect of intermolecular forces that vary among different mineral systems and fluid confinement results in unique (and, poorly constrained) perturbations to a wide range set of thermodynamic and transport parameters, different from those observed in the bulk phase. It is a formidable challenge to characterize the fluid behavior (e.g. phase transitions, molecular orientation and relaxation, diffusion, adsorption, contact angle, surface tension, etc.) within internal nano-pore or fracture networks. This presentation will provide an overview of the application of state-of-the-art experimental, analytical and computational tools to assess key features of the fluid-matrix interaction. The multidisciplinary approaches highlighted will include neutron scattering, thermodynamic measurements and molecular-level simulations to quantitatively assess molecular properties of different mixtures of C-O-H fluids in nanpores. Key results include: (a) The mobility of a hydrocarbon (methane, propane, butane) is enhanced in the presence of another non-polar fluid such as CO2 due to the preference for CO2 to adsorb and wet SiO2 pore walls, (b) Methane solubility in water is enhanced in silica nanopores at elevated pressures and ambient temperature compared to bulk values. (c) The methane solubility in nano-confined water strongly depends on the confining substrate, (d) -The diffusivity of methane in nanopores is highly dependent on substrate type and its effect on water structure, its free energy landscape and hydrogen bonding on the surface where the order for methane diffusion rate is SiO2&gt;MgO&gt;Al2O3&gt;muscovite=calcite.

Behavior of supercritical C-O-H fluids in nanoporous materials

255th National Meeting (2018)

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