Experimental Study on Mechanical Properties, Permeability and Acoustic Emission Characteristics of Gypsum Rock Under THM Coupling

The mechanical properties and permeability of gypsum caprock have a significant influence on the tightness and stability of salt cavern gas storage, a series of tests were carried out to investigate the mechanical properties, permeability and AE characteristics of gypsum under THM coupling in this work. The peak strength of gypsum increases with the increase of confining pressure and the decrease of temperature, the failure and dilatation failure criteria are obtained by utilizing Mogi failure criterion. The permeability decreases with the increase of temperature in the compaction and linear elastic deformation stage, and the final permeability decreases with the increase of temperature under the confining pressure of 5 MPa and 15 MPa, while increase with the increase of temperature under the confining pressure of 25 MPa and 35 MPa. And the permeability decreases with the increase of confining pressure in the whole test process because of the constrain of confining pressure on the formation of microcracks and pores. The best fitting formulas of the relationship between permeability and confining pressure is given by fitting at 25 °C and 110 °C, which can be expressed by two exponential functions. The AE characteristics also confirmed that the increase of confining pressure and temperature inhibited the formation of microcracks and pores, and the AE peaks have the same hysteresis effect as the stress peaks. It is noted that the peaks of AE ring count increase with the increase of temperature under the confining pressure of 35 MPa.