Structure, Dynamics and Reactivity of C-O-H Fluids in Nanoporous Regimes Relevant to Unconventional Reservoirs

Abstract:

Many unconventional reservoir lithologies are comprised of pore regimes ranging from relatively uncommon large macropores at the millimeter scale to more numerous small micropores at the sub-micron and nanometer scale. The size, distribution and connectivity of these confined geometries, the chemistry of the solid, the chemistry of the fluids and their physical properties collectively dictate how fluids migrate into and through these micro- and nano-environments, wet and ultimately react with the solid surfaces. Our current understanding of the rates and mechanisms of fluid and mass transport and interaction within these multiporosity systems at the molecular scale is far less robust than we would like.

This presentation will take a two-fold approach to this topic area. First we will provide a brief overview on pore types and their relationship with mineralogy in key gas shale formations with special emphasis on the Utica/Pt. Pleasant and Eagle Ford. We will highlight results from conventional methods such as SEM along with more sophisticated approaches including small- and ultra-small angle neutron scattering that contribute to two key science question areas: (a) What are the size, distribution, connectedness, and contribution to total porosity of nano- to micropores in representative gas shales? and (b) How do these pore features vary with the distributions of clay and carbonate matrix and organic matter? The second more in-depth part of the presentation will focus the application of state-of-the-art experimental, analytical and computational tools to assess key features of the fluid-matrix interaction relevant to shale settings. The multidisciplinary approaches highlighted will include neutron scattering and NMR experiments, thermodynamic measurements and molecular-level simulations to quantitatively assess molecular properties of pure water, aqueous electrolytes and simple immiscible water-hydrocarbon mixtures confined to well-characterized porous media, subjected to temperatures and pressures relevant to subsurface energy systems. These studies conducted in concert are beginning to provide a fundamental understanding at the molecular level of how intrinsically different C-O-H fluids behave in confined geometries compared to bulk systems.