Experimental on the pore structure characteristics of Longmaxi Formation shale in southern Sichuan Basin, China

Abstract

In this paper, the pore structure characteristics of shale samples from the Lower Silurian Longmaxi Formation in South of Sichuan Basin of China were investigated by total organic carbon (TOC) content determination, X-ray diffraction (XRD), scanning electron microscope (SEM), low pressure nitrogen adsorption (LPNA) and high pressure mercury injection (HPMI). The fractal dimension of shale samples was calculated based on Frenkel-Halsey-Hill (FHH) model and thermodynamic relation model. The results showed that the major mineral compositions of shales were quartz and clay content. Organic pores, intergranular pores, intragranular pores, microfractures were widely developed in the shale samples, of which organic pores were the most developed. The pore morphology was mainly ink bottle-shaped pores and slit-shaped pores; the pore size distribution of shale samples was complex with multiple distribution peaks, the pore size between 3 and 40 nm occupied the most of storage space. The fractal dimension Dn1 of pores between 2 nm and 10 nm was 2.7177–2.7933, while fractal dimension Dn2 of pores between 10 nm and 50 nm was 2.2439–2.5468. The fractal dimension Dr of macropores calculated by the thermodynamic model was 2.6401–2.7025.