Abstract: This paper studies the meso-damage evolution of the structure of the brittle shale after hydration. Hard brittle shale samples at different soaking times are measured with the nuclear magnetic resonance (NMR) technique. The quality of the sample, transverse relaxation time T2 spectrum distribution and nuclear magnetic resonance imaging of the hard brittle shale samples at different soaking times are obtained. The results show that hydration can produce damage inside the rock. The water absorption of the samples changes a lot in the first eight hours and shows no obvious change after one day. The microcrack propagates rapidly and the surface cracks are formed as the soaking time increases. NMR image shows that the internal microstructure of the sample redistributes under hydration effect. T2 signal amplitude curve changes significantly as the soaking time increases. The hydration damage process is divided into three stages: the development stage of the large size pore cracks, the formation of the small pores and the propagation of the large size pore cracks, the propagation of the small size pores and the formation of the large size pore through cracks. NMR image shows the internal microstructure of the same sample at different soaking times. The hydration damage process of rocks is shown dynamically.

Key words: hard brittle shale, hydration damage, nuclear magnetic resonance (NMR), relaxation time, microcrack