Microstructural characterisation of organic matter pores in coal-measure shale

Abstract

To gain the insight into the nature of organic matter (OM) micro-nanometer pores and fractal features of coal-measure shale from the OM macromolecular evolution perspective, 28 Taiyuan formation shale samples are collected from Qinshui Basin and characterized with Rock-eval, Field emission scanning electron microscope (FE-SEM), low-pressure N 2 gas adsorption (Lp-N 2 GA) and Fourier transform infrared spectroscopy (FTIR). The results show that OM is in the high-over mature stage. Pore size ranges from 5.7 to 26.7 nm and pores less than 4 nm are dominant. Two pore fractal dimensions D 1 and D 2 are obtained from Lp-N 2 GA with the Frenkel-Halsey-Hill method, which are in the range of 2.272-2.617 and 2.561-2.799, respectively. A series of FTIR structure parameters are obtained by peak fitting the FTIR spectra to describe the microstructure of OM molecules, such as length of aliphatic chain, degree of aromatic carbon condensation and hydrocarbon generation potential. Micro-nanometer OM-related pores in FE-SEM images can be classified as OM hydrocarbon-generating pores, OM structure pores, OM intergranular pores and micro- cracks, with the first being most developed. Both hydrocarbon-generation and condensation of aromatic nucleus have positive effects on D 1 . Hydrocarbon-generation is more effective for the development of micropores, while the condensation of aromatic nucleus is more conducive for the development of mesopores (<10 nm). The higher the total organic carbon content, and the more the micropores and mesopores (<10 nm) develop, the higher the value of D 1 . Cited as : Li, K., Kong, S., Xia, P., Wang, X. Microstructural characterisation of organic matter pores in coal-measure shale. Advances in Geo-Energy Research, 2020, 4(4): 372-391, doi: 10.46690/ager.2020.04.04