ObjectiveUnderground gas storage (UGS) systems are critical for ensuring the flexibility, reliability, and safety of natural gas supply. Microseismic monitoring has emerged as a key technology for assessing the integrity of caprock seals and evaluating dynamic geomechanical responses during gas injection and withdrawal operations. This study aims to systematically summarize the technical framework, implementation practices, and engineering benefits of microseismic monitoring in UGS applications.

MethodsThe study integrates technical principles and field experiences from a range of UGS types, including depleted reservoirs, aquifers, and salt caverns. Monitoring approaches are categorized into surface, shallow-borehole, and deep-borehole networks. Key procedures including signal preprocessing, phase picking, event detection, location methods (arrival-time based and waveform stacking), and mechanism analysis are reviewed. Case studies from China (e.g., Hutubi, Tangshan M, and Jintan UGS) and Europe (e.g., Minerbio, Stenlille, Castor) are analyzed to demonstrate the effectiveness of microseismic monitoring under varying geological conditions.

ResultsQuantitative findings from multiple UGS sites indicate that microseismic events typically range from M_L −3.0 to 2.0, reflecting subtle stress perturbations. For instance, 229 events were recorded at the Hutubi UGS, exhibiting scattered distributions away from major faults and indicating effective caprock sealing. At the Jintan salt cavern UGS, 419 events within 23 days revealed dense clustering near cavern boundaries, enabling real-time evaluation of cavern stability. At the Tangshan M oilfield-based UGS, limited events were detected despite pressures exceeding 30 MPa, with analysis revealing insufficient sensitivity of surface and shallow monitoring arrays for 4-km-deep reservoirs. Comparative analysis of injection parameters and microseismicity demonstrated a stronger correlation with pressure variation than with injection volume. Additionally, the Castor UGS failure case in Spain, where delayed detection of fault reactivation led to M 4+ earthquakes and project termination, highlights the consequences of inadequate real-time monitoring.

ConclusionMicroseismic monitoring enables real-time assessment of stress evolution and caprock integrity, supporting risk mitigation and operational optimization throughout the UGS lifecycle. Gas and oil reservoir-type UGSs prioritize deep fault reactivation monitoring, while salt cavern UGSs focus on cavern wall deformation. Deep borehole sensors and dense arrays are essential for improving detection thresholds and depth accuracy. Future advancements should integrate fiber-optic sensing, machine learning algorithms, real-time data streaming, and interdisciplinary modeling to enhance early warning capability and ensure long-term operational safety of UGS systems.