Experimental investigation on the mechanical and acoustic emission characteristics of shale softened by water absorption

Shale is a fine-grained, clastic sedimentary rock composed of clay minerals and other minerals. The water-shale interaction plays an important role in the borehole drilling and hydraulic fracturing during the process of shale gas exploitation. In this study, laboratory experiments, including water absorption experiments and uniaxial compression tests, were used to investigate the mechanical behaviours of the water-absorbing shale specimens. From the laboratory experiments, the following statements can be drawn: a) the water-absorbing shale specimens experience longer compaction and crack closure stages than the natural shale specimen; b) the mechanical properties of the water-absorbing shale specimens, such as uniaxial compressive strength, Young's modulus and peak strain, are less than those of the natural shale specimens; c) the apertures of the failure cracks in the water-absorbing shale specimens are greater than those in the natural shale specimens under uniaxial compression loading. The acoustic emission technique was also used to capture the acoustic emission events of the shale specimens during the uniaxial compression tests. By the acoustic emission analysis, it is concluded that the water absorption stimulates the AE events in the shale specimens.