Pore characteristics of a shale gas reservoir and its effect on gas content

The porosity tests of 24 Longmaxi Formation shale samples fromthe southeastern Chongqing area and 10 Xujiahe Formation shale samples fromthe southeastern Sichuan area were carried out with argon ion milling+ scanning electron microscopy (SEM) and nitrogen adsorption methods. The effect of porosity difference on gas content was discussed. Shale pores are usually organic pores, mineral inter-particle pores,dissolution pores, inter-granular pores and inter-laminar cleavage cracks, and most of the pore shape was irregular and open.The pore structure of the samples was complex. Nano-scale organic pores were common in the Longmaxi Formation shale samples, and the pore diameter was 2-10 nm. Inorganic middle-large pores and micro-cracks were dominant in the Xujiahe Formation shale samples. The pore characteristics might result from different chemical mole-cular properties of organic matter in the shale, or a catalytic relationship between inorganic mineral or element and organic matter. Statistical results showed that the pore types were not the main controlling factors of gas content: TOC was the most essential factor for shale gas reservoir.The pore structure of the Xujiahe Formation shale samples was mainly affected by inorganic minerals.TOC was the dominant factor of specific surface area and 2-10 nm pores in the Longmaxi Formation shale samples, and provided the main storage space for shale gas.Illite was an important factor for 2-10 nm pores, which provided the main storage space for the Xujiahe shale gas.