Abstract
In recent years, the shale gas in the southern Sichuan Basin has achieved great commercial development, and the Silurian Longmaxi Formation is the main development stratum. In order to solve the problems of great difference production and inaccurate gas content of the Longmaxi Formation shale gas field in the southern Sichuan Basin, based on thin section identification, argon ion polishing-field emission scanning electron microscopy, high pressure mercury injection, low temperature nitrogen adsorption and the fractal method, the micropore structural heterogeneity of the siliceous shale reservoir of the Longmaxi Formation has been studied. The results show the following: The pores of siliceous shale are mainly intergranular pores and organic pores. Image analysis shows that there are obvious differences in size and distribution of shale pores among different types. The micropore structural heterogeneity is as follows: intragranular pore > intergranular pore > organic pore. In the paper, the combination of low temperature nitrogen adsorption method and high-pressure mercury injection method is proposed to characterize the micropore size distribution and fractal dimension, which ensures the credibility of pore heterogeneity. The shale pores are mainly composed of mesopores (2–20 nm), followed by macropores (100–300 nm). For different pore sizes, the fractal dimension from large to small is mesopore, micropore and macropore. Shale pore structure and fractal dimension are correlated with mineral composition and total organic carbon (TOC) content, but the correlation is significantly different in different areas, being mainly controlled by the sedimentary environment and diagenesis.
Highlights
Marine shale is well developed in China, with huge thicknesses of source rock and favourable conditions for hydrocarbon generation
Previous studies have proved that there are many factors, such as pore structure, organic carbon content, mineral composition, gas content and fracture development affecting the heterogeneity of the shale reservoir, among which pore structure is one of the most important factors [11,12]
Total organic carbon (TOC) is an important index of shale reservoir, which can effectively evaluate the abundance of shale organic matter
Summary
Marine shale is well developed in China, with huge thicknesses of source rock and favourable conditions for hydrocarbon generation. In recent years, following the guidance of the North American, the exploration and development of shale gas in China has progressed remarkably. Sichuan exceeded 6 × 109 m3 and 3 × 109 m3 , respectively, which set off an upsurge of shale gas exploration and development in China [6,7,8]. Previous studies have proved that there are many factors, such as pore structure, organic carbon content, mineral composition, gas content and fracture development affecting the heterogeneity of the shale reservoir, among which pore structure is one of the most important factors [11,12]. Many qualitative and quantitative multidisciplinary techniques have been used to characterize shale pores. TOC content is mainly determined by geochemical experimental analysis method [28]
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