Abstract
Pyrite is widely distributed in the Longmaxi marine shale in the Upper Yangtze area of China. Pyrite, one of the important components of shale, has an important influence on the enrichment of shale gas. However, there are currently only a few studies on this topic. Based on shale samples from drilling cores using field emission scanning electron microscopy, the pore characteristics of pyrite from the Longmaxi Formation in the Upper Yangtze area of China are studied. The results showed that the intergranular pores of pyrite and abundant organic pores in the organic matter pyrite assemblages are developed in the Longmaxi Formation shale in the study area. Most pyrite framboid pores have triangular or irregular quadrilateral shapes, with pore diameters ranging from 0 to 240 nm. Pores with diameters of 80–240 nm are the major reservoir spaces for shale gas within the pyrite framboids. The average contribution rate of pyrite framboids to shale pores reaches 3.21%, and the highest contribution is 5.66%, indicating that the pyrite pores may have a favorable contribution to the shale reservoir pore system, but the contribution degree is low.
Highlights
In recent years, the exploration and development of shale gas have achieved a great success in North America and the Sichuan Basin in China (Hao et al, 2013; Chen et al, 2015; Zou et al, 2016; Chen et al, 2019; Shu et al, 2020), which has attracted worldwide attention
The common pore types in pyrite in the Longmaxi Formation shale in the Upper Yangtze area are as follows: abundant organic pores are developed in the organic matter pyrite assemblages; these pores are the most common type of pores that are closely related to pyrite in the Longmaxi Formation shale (Figure 3)
Taking multiple photographs of 8 shale samples in different visual fields by using field emission scanning electron microscopy (FE-SEM) and calculating observation statistics on the pores in the pyrite framboids, the results showed that intracrystalline and organic pores are developed in pyrite framboid aggregates, with organic pores prevailing
Summary
The exploration and development of shale gas have achieved a great success in North America and the Sichuan Basin in China (Hao et al, 2013; Chen et al, 2015; Zou et al, 2016; Chen et al, 2019; Shu et al, 2020), which has attracted worldwide attention. Nanopores in shale reservoirs are well developed in diverse types and structures, effectively providing storage space for shale gas. The structural characteristics of nanopores are important and difficult aspects of the theoretical study of shale gas geology (Ross and Bustin, 2008a; Clarkson et al, 2013). Pore characteristics are important determinants of the gas content in shale gas reservoirs and are the keys to shale reservoir evaluation. Studying the pore characteristics of reservoirs is of great significance for shale gas exploration, development, and resource potential evaluation (Loucks et al, 2009; Roger and Neal, 2011; Gao et al, 2019). Scholars have performed many studies on the pore characteristics and structure of marine shale, including different types of pores, pore structures, and connectivity of shale gas reservoirs on different scales
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