Experimental study on permeability evolution of sandstone under cyclic loading

Abstract

The permeability of a rock mass affects the site selection and construction of underground high-pressure gas storage for compressed-air energy storage. This study investigates the permeability evolution of sandstone under high-pressure gas during the cycle of confining and axial pressures. Nitrogen permeation tests were conducted at different inlet pressures using the steady-state method. The initial steady-state flow, seepage in the circulation, and steady-state flow after circulation were measured continuously in three stages. The effects of the loading and unloading rates and load-holding time on the seepage flow were analyzed. The results indicate that the flow rate and displacement changed with periodic changes in the axial and confining pressures during the cycle. The higher the inlet pressure, the greater was the difference between the peak and trough of the flow in the cycle, and the greater was the difference between the flow after the cycle and the initial flow. When the inlet pressure was 10 MPa, the steady-state flow rate increased from 284 ml/min to 336 ml/min (18%). When the inlet pressure was 2 MPa, the evolution range of the seepage flow in the sample was similar for different load-holding times. The loading and unloading rates had a significant influence on the flow waveform in the circulation process but little influence on the wave height. With an increase in the number of cycles, the porosity of the samples first decreased rapidly and then increased slowly. This study provides a reference for construction and operation of compressed-air energy-storage systems.