It is of great significance to explore the compression effect of shale matrix in mercury intrusion method and reveal the characteristics of pore heterogeneity for the study of shale gas occurrence mechanism. In order to investigate the matrix compressibility of shale and the multifractal characteristics of pore size distribution (PSD), the shale samples in Qinshui Basin were collected to investigate the compression effect and its influencing factors of shale during mercury intrusion method by integrating the low temperature nitrogen gas adsorption and mercury intrusion porosimetry experiments. Based on the corrected experimental data and multifractal theory, the multifractal behavior of PSD is characterized. The results show that the compressibility of the samples ranges from 0.154×10^-5/MPa to 4.74 ×10^-5/MPa when the pressure is from 15MPa to 413MPa. Comparing the total volume of uncorrected mercury intrusion with the corrected total volume, the significant change (27.75 % to 163.25 %) indicates that the matrix compression has a significant effect on the mercury intrusion experimental results. The corrected mercury injection data can more accurately reflect the real structure of PSD in porous media. The difference of material composition is the key factor to determine the strength of compressibility, and the shale samples with different material components show different compressibility. The higher clay mineral content and organic matter content are, the larger their compressibility coefficients; while higher quartz and feldspar contents result in smaller compressibility coefficients. The partition function diagram and mass scaling function curve of shale samples show good self-similarity and multifractal characteristics, respectively. The median pore diameter shows positive correlation with right spectral width D(-10)-D(0), left spectral width α(-10)-α(0), as well as singular index α(0). The high Median Pore Diameter reflects that the low probability density area has obvious advantages and the pore structure is complex. In addition, the low probability density area of shale samples with well-developed mesopores and macropores is dominant in pore heterogeneity. The pore heterogeneity distribution of shale samples has a two-stage relationship with total organic carbon content ( TOC ). When the TOC content is about 2 %, the pore size distribution of shale shows the “mutation point” of heterogeneity and pore connectivity.

Matrix compression; Multifractal; Heterogeneity; Pore size distributions; Shale