Characterization and Adsorption Investigations of the Nanostructure of Gas Shales

Due to the complexities involved in the analysis of micro- and mesoporous gas shale, a combined theoretical and experimental approach has proven to provide increased insight into the adsorption characteristics of methane (CH4) and carbon dioxide (CO2). Pore characterization techniques are used to provide information for theoretical modeling efforts, such as pore volume and pore size distribution (PSD). Idealized powdered shale sorption isotherms are created by varying incremental amounts of kerogen, illite, quartz, and calcium carbonate (CaCO3). The kerogen and illite have been shown to be the most vital for micropore measurements. The kerogen was obtained from Silurian shale, while Green River illite was used for the clay component and the rest was composed of equal parts by weight of silica (SiO2) to represent quartz and CaCO3 to represent the carbonate components. Baltic, Eagle Ford, and Barnett shale sorption measurements were used to validate the idealized samples. The idealized and validation shale sorption isotherms were measured using low-pressure N2(77K), Ar (87K) and CO2 (273K) adsorbates on a Quantachrome Autosorb IQ2 instrument. A subset of these samples was also measured using CO2 and CH4 adsorbates under subsurface temperature and pressure conditions using a Rubotherm magnetic suspension balance. The shale samples were processed using outgassing temperatures that did not affect the structures of kerogen and illite, while removing adsorbed gas species, such as H2O and CH4. This data lends itself toward the development of predictive models weighted and scaled by the percentages of these essential shale components to provide accurate gas-in-pace estimates of both CH4 and CO2.