Influence of particle size on gas-adsorption experiments of shales: An example from a Longmaxi Shale sample from the Sichuan Basin, China

Abstract

To explore the optimum particle size range for low-pressure gas adsorption experiments of shales, a sample of the Longmaxi shale from the Sichuan Basin, China, was crushed into various particle sizes between 4 and 0.058mm. Low-pressure CO2 and N2 adsorption experiments were then performed on these crushed samples, and the pore volume, surface area, and pore size distribution (PSD) were determined from isotherms of gas adsorption. Variations in the volume of sorbed gas, pore volume, surface area, and PSD were recorded across the two series of experiments. In the CO2 adsorption experiments, in which particle size ranged from 4 to 0.83mm, sorbed gas volume, pore volume, and surface area increased with decreasing particle size. No obvious changes were found in sorbed volume, pore volume, surface area, or PSD for the samples with particle sizes from 0.83 to 0.058mm. In the N2 adsorption experiments, the sorbed gas volume and surface area increased with decreasing particle size in samples from 4 to 0.113mm, whereas no obvious variations were observed in the 0.113–0.058mm samples. Similarly, pore volume and PSD showed clear changes with decreasing particle size for the 4–0.113mm samples. The results show that 0.113mm (130 mesh) is the optimum particle size for low-pressure CO2 and N2 adsorption experiments that seek to analyze the characteristics of shale reservoirs.