Extraction of shale gas and light hydrocarbons and geologic storage of carbon dioxide play major and increasing roles in the U.S. energy industry. 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.<br/>Quantification of these phenomena in the chemically and structurally heterogeneous environments found in rock pores cannot be obtained directly, but only through a combination of experimental and modeling techniques. Neutron scattering and excess sorption measurements were utilized to measure the alkane sorption properties in the nm sized pores. Molecular modeling 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 organic-rich shale samples.<br/>The excess sorption of supercritical carbon dioxide was measured in 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 were used to 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 and propane in different porous materials (i.e., silica aerogel, CPG-10, and montmorillonite clay) were measured for different conditions of pressure and temperature. In combination with Monte-Carlo modeling, molecular-level pictures of the sorption behaviors of these fluids are obtained and give detailed insight into confined fluid properties and fluid-solid interaction potentials.

Adsorption of light hydrocarbons and carbon dioxide confined in nanoporous synthetic sandstone rocks and shale

249th National Meeting (2015)

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