Construction and detection capability evaluation of the microseismic monitoring system for the Chongqing Xiangguosi underground gas storage

Focusing on the Chongqing Xiangguosi reservoir-type underground gas storage (UGS), this study addresses its geological safety monitoring in the complex structural environment. A three-stage network construction approach—pilot testing, optimization, and system refinement—is proposed and implemented. As a result, an integrated deep–shallow microseismic monitoring network consisting of 12 shallow wells and 2 deep wells is established. The performance of the monitoring network is systematically evaluated based on the Brune source spectrum theory and quantitative analysis of noise power spectral density (PSD). The shallow-well system is capable of detecting events of ML ≈ −0.5, with a location accuracy of less than 50 m, whereas the deep-well system achieves higher sensitivity (ML ≈ −2.5) and better location accuracy (<15 m) in the structural core area. Monitoring data from the trial operation indicate no significant correlation between microseismic activity and gas injection and production operations, nor any anomalies in fault activity or caprock response. These results preliminarily verify the sealing integrity and stability of the gas-storage trap during the current monitoring period. The technical framework—characterized by a deep–shallow collaborative architecture, quantitative capability assessment, and statistical empirical analysis—provides a generally applicable reference scheme for the design optimization and engineering application of microseismic monitoring systems for similar underground gas storage facilities.