Seismic monitoring is an effective reservoir management technique for CO2 capture and storage （CCS）and enhanced oil recovery（EOR）projects. However, seismic monitoring in onshore fields often faces challenges associated with inadequate repeatability. The possible factors are positioning errors for sources/receivers and changes in near-surface conditions between monitor surveys. Permanent seismic monitoring（PRM）using both stationary sources and receivers can overcome this problem.
JOGMEC has continued to research seismic monitoring using a permanent seismic source（accurately controlled routinely operated signal system: ACROSS）which consists of a rotary eccentric mass and a motor anchored on a concrete foundation. Since 2014, JOGMEC has conducted a demonstration test at the Aquistore CCS site. Four seismic surveys using a single ACROSS and a sparse permanent geophone array were performed from 2016 to 2020.
This paper reports the application of analytical techniques of seismic reflection surveys on reservoir monitoring using a single ACROSS source at the Aquistore CCS site. Before analyzing the real data, we performed a seismic modeling study to validate that our approach can ideally capture time-lapse signal responses. Then, we applied seismic data processing and time-lapse analysis to the four monitor datasets. As a result, seismic responses associated with injected CO2 were successfully detected around the injection well at the reservoir depth. Compared to the conventional 3D seismic monitoring result acquired using dynamite sources, a similar growth pattern of the seismic responses was observed.
In conclusion, a PRM system using the ACROSS can be an effective approach to realize long-term continuous reservoir monitoring at low cost. It is possible to capture the outline of reservoir changes with just only a single source, but the use of multiple sources is desirable to improve reproducibility. It is also important to pursue establishing techniques that maximize the performance of the ACROSS.
