Effect of Acid Action Time on Microscopic and Mechanical Properties of Shale

To explore the evolution of shale properties with the action time of acid solution, CT scanning, nuclear magnetic resonance technology and uniaxial compression experiment were carried out. The pore characteristics and mechanical properties evolution of shale after different treatment time (0 ~ 80 days) were characterized and analyzed. The results show that with the increase of immersion time of acid solution, new meso-fractures are gradually formed in the shale matrix and expand continuously, the total pore, macropore and mesopore porosity of shale increase gradually, while the micropore porosity decreases gradually. The fractal dimension increases gradually with the increase of acid immersion time, which means the pore structure of shale becomes more and more complex. The increase of porosity in acidic aqueous solution enhances the damage variable of shale, and finally leads to the weakening of uniaxial compressive strength and elastic modulus.