Application of real time micro-seismic technique to the stability monitoring of salt cavern gas storage

Salt cavern gas storages are often faced with the problems of safety and stability, such as surface subsidence, salt rock failure, gas leakage and fast cavity shrinkage. In order to monitor the stability of the cavity in the process of water or gas injection and brine discharge, so as to ensure the stable and safe operation of gas storage, a real-time micro-seismic technique was used to monitor the Jintan salt cavern gas storage continuously for 12 days. A high-precision geophone was placed downhole to receive the micro-seismic events in the process of production. The factors inducing the micro-seismic events in the process of solution mining and gas injection/production were investigated and the characteristics of different micro-seismic signals were analyzed comprehensively. It is shown that the micro-seismic signals of the gas storage are attenuated seriously if the geophone is set in the three-layer casing and the liquid in the casing annulus is especially fatal to transverse wave propagation. It is indicted that some observed micro-seismic events may be caused by the collapse or rupture of the cavity wall and the quantity of micro-seismic signals is increased sharply due to the variation of water injection and brine discharge parameters. It is demonstrated from the current micro-seismic signal statistics that the current production parameters can guarantee the stable and safe operation of gas storage.