3:30 PM - 3:45 PM
[HSC06-07] Continuous monitoring system for onshore and offshore CO2 storage sites
Keywords:CO2 storage, Monitoring, Seismic source, DAS, ASV
Reducing a large amount of CO2 by CCS to achieve the IEA 1.5 °C scenario requires thousands of large-scale CO2 storage sites (~ 1 million tons/year) in the world. To achieve such a large number of CO2 storage sites, we should manage multi CO2 storage reservoirs distributed in extensive areas using a monitoring system. Monitoring injected CO2 in its reservoir is crucial for predicting the risk of CO2 leakage, increasing efficiency, reducing the cost of CO2 storage, and reducing the risk of induced seismicity. Also, the information derived from monitoring is vital to obtain public acceptance for the projects. Here, we report a new continuous monitoring system for CO2 storage sites in onshore and offshore environments, based on small seismic sources and distributed acoustic sensing (DAS).
The seismic source in our system generates continuous waveforms with a wide frequency range. Because the signal timing is accurately controlled, stacking continuous waveforms enhances the signal-to-noise ratio, allowing the use of a small seismic source to monitor extensive areas (multi-reservoir). Onshore field experiments demonstrated that the monitoring signal from the motor-driven source system was detected at a horizontal distance of ~80 km by stacking 4 months of data, suggesting that the system is effective for monitoring an extensive area. Furthermore, temporal variations of the monitoring signal (i.e., seismic velocity) were identified with an error of <0.01% (Tsuji et al., 2021).
To monitor the reservoir in higher spatial resolution and to increase the number of ray paths of the signal, we collected monitoring data using a DAS system based on a fiber optic cable. When we used seafloor cable for DAS measurements, we identified the monitoring signals at >10 km far from the source in high-spatial resolution. Because the monitoring data recorded by DAS can be transferred and analyzed in real-time, we can continuously obtain the monitoring results, making it possible to identify unexpected and rapid changes in reservoirs (e.g., CO2 leakage). Furthermore, to increase the number of seismic sources, we downsize the monitoring source system.
In offshore environments, the deployment of our motor-based seismic source system could be difficult, because the soft seafloor sediment cannot hold the source system. Currently we have designed an unmanned vessel (autonomous surface vehicle; ASV) with the sound source speakers in order to improve the spatial resolution of the monitoring results. If the ASV carrying a small-size speakers continuously generate the monitoring source signals, we can monitor the offshore reservoirs with higher spatial resolution. The numerical simulation results (i.e., CO2 reservoir simulation and dynamic wave propagation simulation) demonstrated that our monitoring systems can monitor the CO2 injected in the reservoirs.
This study demonstrates that multi-reservoir in an extensive area can be continuously monitored at a relatively low cost by combining our seismic source and DAS technology. This work was conducted under the “Sustainable CCS project” of the Ministry of the Environment, Government of Japan.
The seismic source in our system generates continuous waveforms with a wide frequency range. Because the signal timing is accurately controlled, stacking continuous waveforms enhances the signal-to-noise ratio, allowing the use of a small seismic source to monitor extensive areas (multi-reservoir). Onshore field experiments demonstrated that the monitoring signal from the motor-driven source system was detected at a horizontal distance of ~80 km by stacking 4 months of data, suggesting that the system is effective for monitoring an extensive area. Furthermore, temporal variations of the monitoring signal (i.e., seismic velocity) were identified with an error of <0.01% (Tsuji et al., 2021).
To monitor the reservoir in higher spatial resolution and to increase the number of ray paths of the signal, we collected monitoring data using a DAS system based on a fiber optic cable. When we used seafloor cable for DAS measurements, we identified the monitoring signals at >10 km far from the source in high-spatial resolution. Because the monitoring data recorded by DAS can be transferred and analyzed in real-time, we can continuously obtain the monitoring results, making it possible to identify unexpected and rapid changes in reservoirs (e.g., CO2 leakage). Furthermore, to increase the number of seismic sources, we downsize the monitoring source system.
In offshore environments, the deployment of our motor-based seismic source system could be difficult, because the soft seafloor sediment cannot hold the source system. Currently we have designed an unmanned vessel (autonomous surface vehicle; ASV) with the sound source speakers in order to improve the spatial resolution of the monitoring results. If the ASV carrying a small-size speakers continuously generate the monitoring source signals, we can monitor the offshore reservoirs with higher spatial resolution. The numerical simulation results (i.e., CO2 reservoir simulation and dynamic wave propagation simulation) demonstrated that our monitoring systems can monitor the CO2 injected in the reservoirs.
This study demonstrates that multi-reservoir in an extensive area can be continuously monitored at a relatively low cost by combining our seismic source and DAS technology. This work was conducted under the “Sustainable CCS project” of the Ministry of the Environment, Government of Japan.