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Experimental study of sealing performance:2. Effects of particle size distribution on threshold pressure of sintered compacts

In connection with an assessment of the sealing performance of a caprock such as mudstone for geologic CO2 sequestration, we prepared sintered compacts comprising two different‐sized silica beads with various particle size ratios and mixing ratios. Then we examined the correlation between permeability k and threshold pressure Pcth of the samples. Specifically, Pcth was measured in supercritical CO2‐water system under conditions of 1000 m depth (10 MPa and 40°C). A series of studies was conducted to identify factors affecting data variability on the Pcth‐k correlation chart and to ascertain the variation ranges of both parameters. This paper corresponds to a second step of work, following previous measurements obtained from monodisperse samples. The sample's k showed good correlation with both the mixing ratio and mean area diameter, whereas Pcth with great variation was correlated with neither parameter. In this context, results suggest that Pcth, which was controlled by local structures within samples, could not be predicted simply from the pore diameter distribution. Regarding the Pcth‐k correlation, monodisperse samples are scattered around the closest‐packing line. In contrast, bidisperse samples are shown mainly below the closest‐packing line. Moreover, the slope of a fitting line on the Pcth‐k double logarithmic chart was lowered from −0.62 for monodisperse particles to −0.43 for bidisperse particles. Nevertheless, the low slope on mudstone cannot be explained solely by the effect of the particle size distribution. Therefore, the contribution of the particle configuration is expected to be greater as a factor affecting the internal structure of mudstone.