Abstract: To undertake the real-time monitoring of the cavity state in the process of water injection and brine displacement, gas injection and production of a salt-cavern gas storage, microseism technology is applied during continuous monitoring for 23 d. The 12-level detector is arranged using the in-well method, and the surface energy source is used for the spatial orientation of the detector. Moreover, the information of the P wave and S wave is combined for spatial orientation of the microseism events. Through a cross analysis on the number of microseism events and injection-production parameters, the influences of production technology on cavity stability are studied. The results show that 419 effective signals occurred during the 23 d monitoring process; sixteen microseism signals are detected in two cavity construction wells, without any obvious signal detected in injection and production wells. Many microseism signals are detected between two injection and production wells, which is considered as natural fracture activity through three-dimensional seismic data obtained with a b-value analysis. The microseism sources are detected as the joint action of shear stress and tensile stress after analytic monitoring, and the sources where tensile stress plays a leading role are more. It is believed that the current injection-production operation parameters meet the safe operation requirements of a salt-cavern gas storage; it is suggested to extend the monitoring time to enhance the microseism quantity and establish statistical laws for injection-production parameters in the follow-up studies, to strengthen the study on natural fracture activity among cavities, thereby ensuring the safe operation of a gas storage.

Key words: microseism, salt-cavern gas storage, stability, water injection and brine displacement, gas injection and production, natural fracture