Advancing Passive/Microseismic Technology to Monitor Subsurface Reservoir During CO2 Injection

Summary This study presents the application of an integrated passive seismic monitoring approach for tracking CO₂ injection in a live enhanced oil recovery (EOR) project operated by ADNOC in the UAE. The monitoring system combines microseismic and passive seismic methods—specifically Full Wave Location (FWL) and Low Frequency Seismic (LFS)—to characterise reservoir dynamics across a broad frequency range (0.1 to >100 Hz). A field array of 1C and 3C sensors was deployed in a grid configuration to optimise spatial coverage and data fidelity. Calibration tests and onsite suppression of surface waves were performed to enhance signal quality. FWL was employed to locate microseismic events and derive moment tensors, providing insights into fracture reactivation and pressure-induced changes in the reservoir. LFS was used to analyse spectral responses from ambient seismic noise to delineate zones of CO₂ saturation based on velocity changes. The results included delineation of fluid contacts, identification of injection-driven reservoir changes, and detection of elevated microseismic activity. The monitoring also enabled assessment of caprock integrity and mapping of horizontal stress variations. These findings support the application of passive seismic methods for continuous CO₂ reservoir monitoring in subsurface storage operations