The effect of sample particle size on the determination of pore structure parameters in shales

The relative standard deviations (RSDs) for Brunauer-Emmett-Teller (BET) N2 surface areas, Dubinin-Radushkevich (D-R) CO2 micropore surface areas and non-local density functional theory (NLDFT) N2 and CO2 nanopore surface areas measurements are < 5%, within analytical error. Therefore, in the studied grain size range (60-200 mesh), the sample particle size shows insignificant effects on surface area results. However, samples with smaller particle size have a greater effect on pore volume and pore size, especially for pore size distribution (PSD) of N2 low-pressure adsorption. The RSDs of the Barrett-Joyner-Halenda (BJH) pore volumes and BET pore sizes of all samples in the 140-200 mesh range are obviously greater than the values of other mesh ranges. Moreover, in the dV/dlogw plots of PSD analysis, high N2 peaks and new N2 peaks appeared in the 10-100 nm pore-width range, particularly for samples in the > 140 mesh range. The 60-140 mesh particle-size range is therefore recommended for N2 low-pressure adsorption. Finally, the sample particle size has insignificant effect on the pore system parameters for grains in the 60-200 mesh range for CO2 low-pressure adsorption. Overall, the results confirm that the 60-140 mesh particle-size range can be used for both N2 and CO2 low-pressure adsorption measurements.