Multifractal Characteristics and Genetic Mechanisms of Pore Throat Structures in Coal Measure Tight Sandstone

The pore structure heterogeneity of ultra-low tight sandstone has a direct impact on the exploration development and sustainable production of tight sandstone gas. In this study, high pressure mercury injection and casting thin sections methods were conducted to study the physical properties and pore structures of Carboniferous-Permian (C-P) tight sandstone reservoirs. Then, the multifractal behaviors of the pore structures and their genetic mechanisms were revealed by establishing the relationships of the multifractal parameter (spectral width of singular spectrum Delta alpha (Delta alpha = alpha(-10)-alpha(10+))) with the petrophysical properties and the lithologic characteristics parameters. The results showed that the multifractal characteristics of the pore throat structure in the C-P sandstone were objective and that the C-P sandstone reservoir of higher mesopores volume tended to display greater pore structure heterogeneity. Moreover, the C-P tight sandstone samples with high debris and less content levels of quartz and feldspar showed stronger pore structure heterogeneity. Furthermore, there was a negative correlation between pore structure heterogeneity and interstitial material while increases in matrix (clay minerals) content and decreases in carbonate and quartz cement had potentially led to the enhancement of pore structure heterogeneity. Additionally, the double effects of tectonic stress caused some of the C-P sandstone samples to display characteristics of strong heterogeneity, low porosity and low permeability.

Automated summary

By studying the physical properties and pore structures of Carboniferous-Permian (C-P) tight sandstone reservoirs, the multifractal characteristics of pore structures and their relationships with lithologic parameters were revealed.