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 (e.g., pores, grain boundaries) will exhibit significant differences compared to bulk fluids. 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 discuss of state-of-the-art experimental, analytical, and computational tools to assess key features of the fluid-matrix interaction under nanoconfinement. The multidisciplinary approaches highlighted will include neutron scattering, thermodynamic measurements, and molecular-level simulations to assess molecular properties of different mixtures of C-O-H fluids in nanpores. Key results include: - Pore size and shape, and pore network tortuosity have a profound impact on orientation and diffusivity, - Molecular “lubrication” leading to increased diffusivity of a hydrocarbon results preferential sorption and wetting of coexisting fluids such as CO2 or H2S on various pore wall types, - Hydrocarbon solubility in water is enhanced in nanopores at elevated pressures (to ~60 MPa) and ambient temperature compared to bulk values, and depends on the confining substrate, - The diffusivity of hydrocarbons in nanopores is dependent on substrate type and its effect on water structure, its free energy landscape and hydrogen bonding, - Despite enhanced solubility in nanopores, the presence of water does result in decreased hydrocarbon diffusivity.

Nanopore confinement of C-H-O mixed-volatile fluids relevant to subsurface energy systems

ACS Spring Meeting 2021

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