STUDY ON FRACTAL CHARACTERISTICS OF MICRO-NANO PORE STRUCTURE OF SHALE

Shale gas, as one kind of unconventional gas, is an important energy supplement. The pore structure characteristic is an important index used to measure and evaluate the storage capacity and fracturing of shale reservoir. The Weiyuan marine shale(1^#), Jiaoshiba marine shale(2^#), Yaoqu tuff(4^#) and Yaoqu continental shale(5^# and 6^#) are selected for tests with mercury porosimetry(MP), N₂ adsorption(NA) and nuclear magnetic resonance(NMR) devices. Based on fractal theory, the relationships between fractal dimensions and pore structure are investigated with MP, NA and NMR to characterize the pore anisotropy. The results illustrate that the fractal dimensions of continental samples 5^# and 6^# are bigger than that of marine sample 2^# in the pore range between 0.1~100 μm based on MP method. The fractal dimensions of marine sample 2^# is bigger than those of continental samples 5^# and 6^# in the pore range of 2~200 nm based on NA method. In contrast, the max fractal dimensions(D_NMR) of marine sample 2^# are about equal to those of continental samples 5^# and 6^# in the pore range between 10 nm to 10 μm by NMR method. Especially, the fractal dimensions of Jiaoshiba marine sample 2^# are biggest among all the samples using NA method. The micropores of Jiaoshiba marine shale are the most development, so the heterogeneity of pore characteristic is the strongest. Therefore, the fractal dimension can be used as an important parameter to evaluate the fracturing effect of shale reservoir and the heterogeneity of pore structure.