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Pores Characteristics and Influencing Factors of Different Types of Shale in China


The shale in China mainly includes three categories, namely marine transitional and lacustrine shale. Various shales have different pore characteristics. Research of development conditions of micropores, mesopores and macropores in various pores, the pore types and morphological characteristics has been conducted through the approaches of gas adsorption and mercury injection. The study found that marine shale has larger specific surface area and pore volume than transitional and lacustrine shale, and transitional shale has the same pore volume as lacustrine shale but larger specific surface area. Above all indicates the marine shale in China with large absorption gas and free gas storage space. There is positive correlation between the pore volume and the specific surface of the three types of shale. The specific surface area of the micropores and mesopores in three types of shale occupies a fairly large proportion, especially the micropores while the macropores give the greatest contribute to the pore volume, caused by nano-micro scale microfractures. According to the N2 absorption-desorption curves, the analysis of different types of pores in three types of shale shows complex pore systems. Both the first type and the third type of pores can be found. The third type of pores (flask-shaped pores) dominate in the marine shale, which is positive for shale gas absorption but negative for shale gas absorption and diffusion while the first type of pores (open tabular pores) prevail in transitional and lacustrine shale, with good connectivity, is conductive for shale gas migration. On the basis of the relationships among specific surface area, pore volume, organic content, clay mineral content, maturity and burial depth, analyzing the main factors controlling the pore characteristics of three pores in shale. There are well correlations among specific surface area, pore volume development conditions and organic matter of three types of shale. However, the differences of organic types can affect development of organic pores. On the one hand, discrepancy in occurrence of organic matter lead to different correlations between three types of shale and clay minerals. On the other, influences of maturity on pores in shale are expressed in two aspects: both organic matter and clay mineral transformation. Meanwhile, compaction and dissolution of organic acid in hydrocarbon-generation process proved especially important to pore structure transformation.