FRACTAL CHARACTERISTICS AND CONTROLLING FACTORS OF SHALE PORE STRUCTURE OF WUFENG-LONGMAXI FORMATION IN THE JIAOSHIBA AREA SOUTHEASTERN SICHUAN BASIN CHINA

The Shale pore structure of the Wufeng-Longmaxi formation in the Jiaoshiba area of southeastern Sichuan is complex, and the clarification of controlling factors is of guiding significance for the effective development of shale gas. Shale pore types were analyzed by organic carbon content, thermal evolution degree, whole-rock X ray diffraction, argon ion polishing electron microscope observation, and low-temperature nitrogen adsorption experiment. Based on the fractal geometry theory of low-temperature nitrogen adsorption, the fractal characteristics of shale pores were studied, and the effects of mineral composition, pore structure, organic matter content, and maturity on the fractal dimension were discussed. Shale pores are mainly organic, dissolution, and intergranular pores, the internal characteristics are mainly ink bottle-shaped and slit type. Shale pores have dual fractal characteristics, and the fractal dimension is between 2.5389 and 2.9126. DI and D2 represent pore surface fractal dimension and structure fractal dimension with relative pressure less than 0.45 and greater than 0.45, DI is between 2.5389 and 2.7199, and D2 is between 2,7343 and 2.9126. Quartz mineral, organic matter content, and maturity positively correlate with D1 and D2, Quartz and organic matter are the carriers of pore development. The maturity of organic matter controls the development of micropores and mesopores of organic matter. Micropores have a greater influence on pore structure parameters. Carbonate minerals and feldspar mainly provide macropores and increase the pore size, which is negatively correlated with D1 and D2. The clay mineral content is also negatively correlated with D1 and D2, directly related to the compaction leading to the simplification of pore morphology and the decrease of micropores.

Automated summary

The shale pore structure in the Wufeng-Longmaxi formation of the Jiaoshiba area in southeastern Sichuan is complex and mainly consists of organic, dissolution, and intergranular pores with dual fractal characteristics. The fractal dimension ranges between 2.5389 and 2.9126, with quartz mineral, organic matter content, and maturity positively impacting pore development. Clay mineral content, on the other hand, has a negative correlation with pore morphological complexity and micropore decrease.