FRACTAL CHARACTERISTICS AND INFLUENCING FACTORS OF PORE STRUCTURE OF MARINE ORGANIC-RICH SHALE

Marine organic shale is the focus of gas exploration and development in China. The fractal characteristics and influencing factors of shale pore structure were analyzed by low-temperature nitrogen adsorption-desorption experiment, scanning electron microscope analysis, organic carbon determination, and X-ray diffraction. The difference of shale mineral composition types of Longmaxi formation in typical areas of the Sichuan Basin is small. Still, the contents of quartz, carbonate minerals, and clay minerals are quite different, and the shale is basically in the stage of over-mature cracking to produce dry gas. The organic pore is an important pore space, and microfractures play an important role in improving reservoir effectiveness. The shale pores have obvious double fractal characteristics, the values of fractal dimensions are concentrated, and the complexity of macropore structure is obviously higher than that of micropore and mesopore. The fractal dimension is related to the content of total organic matter (TOC), the degree of thermal evolution, and mineral composition. The content of organic matter and clay minerals are the most important factors affecting shale pore structure.