Microstructure and SEM-Raman study of organic matter pore heterogeneity in shale

Abstract

The characteristics and influencing factors of pore development in organic matters of shale are of great significance for shale gas exploration and production in China. The pore development in organic matters of shale has been found to be heterogeneous with SEM observation. However, due to the lack of effective approach for micro-scale research, the influencing factors of pore development of organic matter are still controversial. Black shale samples of the Longmaxi Formation of Pingqiao area of the Sichuan Basin were selected by this study and the heterogeneity of development and distribution of pores in organic matters were analyzed in detail from two-dimensional and three-dimensional levels by the means of Ar ion polishing SEM and FIB-SEM observation. The organic matters with different pore development degrees were divided into three levels, and the area occupancy and contribution to the pores of these three levels of organic matter were studied by MAPS. In this paper, the Raman spectrum of three levels of organic matter with different pore development were obtained by SEM-Raman. The main factors affecting the heterogeneity of pore development of organic matter were discussed in view of the differences of Raman parameters. The results showed that the intensity ratio of D peak to G peak of organic matter was different, which indicated that the order degree of aromatic structure of different organic matter was significantly different, proving that the main factor affecting the pore development in organic matter could be the composition of original organic matter. This method can be used to observe the pores of organic matter in micro area and analyze the molecular structure characteristics of organic matter macerals in-situ, and further clarifies the main influencing factors of pore development of organic matter.

Keywords

• scanning electron microscope (sem)
• raman spectra
• heterogeneity
• porosity
• organic matter
• shale