Nano-Scale Pore Structure and Fractal Dimension of Lower Silurian Longmaxi Shale

Abstract

Nanopores of gas shale have important influences on gas adsorption and transport. The nanopore structure of gas shale from Sichuan basin is studied using x-ray diffraction, total organic carbon (TOC), and nitrogen adsorption. Fractal dimensions D₁ and D₂ are calculated from the nitrogen adsorption isotherms and fall in the ranges 2.302-2.638 and 2.847-2.891, respectively. Dependences between the fractal dimensions and TOC, mineral composition, and pore structure can be determined from the experimental data. TOC and clay mineral composition are the key parameters affecting the fractal dimension. Parameter D₁ shows positive correlations with TOC, specific surface area, and total pore volume. Parameter D₂ depends on only the clay mineral component content. Both parameters show a weak negative dependence on the average pore diameter. Fractal analysis can be used successfully to study the pore structure of shale gas reservoirs.