Extraction of shale gas and geologic storage of carbon dioxide play major and increasing roles in the U.S. energy supply. Optimization of these processes requires detailed understanding of the properties of the host matrix and the fluid-rock interactions. The micron- and nm-sized pore systems in rocks comprise the loci for fluid storage and transport. Adsorption of fluid layers at the internal pore walls leads to fluid densification and component enrichment.Understanding of these phenomena in the chemically and structurally heterogeneous environments found in rock pores can be obtained using combination of geochemical rock characterization techniques, neutron scattering and excess sorption measurements. I will illustrate this approach with two examples from our recent work: the adsorption of supercritical carbon dioxide to porous silica glass resembling sand- and siltstone, and the adsorption of methane in quartz-rich shales.The excess sorption of supercritical carbon dioxide was measured in silica aerogel and 2 silica samples with pore sizes of 7.5 nm and 35 nm. Adsorption leads to pore densification at low fluid pressure, which is more pronounced in the narrower pores. The pore fluid density is up to 2 times higher than the corresponding bulk fluid at low pressure. At high pressure, the pore fluid and the bulk fluid have similar densities. This finding implies that carbon dioxide can be efficiently stored in narrow pores at relatively low pressure, thereby significantly reducing the risk of over pressurizing the caprock. Neutron scattering techniques can determine occupancy of pores by fluids and measure the adsorbate structure. Using neutron scattering, the mean density and volume of the fluid sorption phase formed by supercritical CO2 inside silica aerogel were measured. Monte Carlo modeling of the experimental data gives insight into the sorption mechanism and provides molecular-level fluid density maps. Neutron scattering measurements of ethane and propane dynamics in porous silica samples was studied by quasielastic neutron scattering.

Sorption and nanoscale structure and dynamics of geofluids confined in rock pores

248th National Meeting (2014)

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