Microseismic Monitoring with Borehole DAS During CCUS Operations Onshore Japan

Summary We conducted a continuous distributed acoustic sensing (DAS) measurements in an onshore carbon capture utilization and storage (CCUS) pilot field in Japan, focusing on microseismic monitoring over a 70-day period from pre-injection to post-injection. Two fiber optic cables were installed behind the production casing of two wells, each used as both a producer and injector. To efficiently detect microseismic events, we utilized two automated detection systems: a machine learning (ML)-based approach and a migration-based approach. The ML-based system successfully identified a number of events, while the migration-based system provided more reliable outcomes. Approximately 1,200 events were detected automatically, including natural events, operation-induced events such as perforations, and artificial noise. No significant changes in seismicity attributed to CCUS operations were observed. We compared DAS data with data from an existing network using high-sensitivity three-component velocity seismometers installed in shallow boreholes. Our analysis confirmed that DAS significantly enhanced microseismic event detectability near the injection zone. Beyond broadband DAS data for microseismic detection, low-frequency DAS data were also recorded. This additional dataset provides valuable insights for monitoring injection and production behaviors and assessing well integrity during CCUS operations.