11:30 〜 11:45
[HSC04-10] Permanent deployment of seismic sources and receivers for real-time monitoring of CO2 plume
キーワード：CO2地中貯留、光ファイバー、分布型音響計測、モニタリング
Permanent deployment of seismic sources and receivers is one way to reduce labor and costs significantly for real-time CO2 plume monitoring. As permanent receivers, the distributed acoustic sensing (DAS) is now widely adopted for borehole seismic. The small dimension of fiber optic cables increases possibility to install in narrow spaces, like annulus behind a casing pipe. Surface orbital vibrators (SOVs) are an option as the permanent seismic sources, which consist of a rotating eccentric mass spun to high velocity. The SOVs are bolted to a few cubic meters of concrete foundation for better coupling with subsurface, which results in very low mobility of apparatuses. The system can also be fully automated without on-site operators.
Data quality of SOVs-DAS acquisitions is one of key factors to be considered for time-lapse seismic monitoring of CO2 plume. The energy of SOV’s single sweep is much weaker than a single sweep by a vibroseis truck. The walk-away VSP (vertical seismic profiling) imaging can improve the signal-to-noise ratio with stacking multiple data swept at multiple source points, while offset VSP imaging from a single source point by SOVs can be improved only by increasing of number of vertical stacks.
To optimize acquisition parameters, we analysed the baseline survey data from SOV-DAS acquisition at CCS project in ND, USA. The four installations of SOVs and two wells (injection and observation wells) are aligned as a 2D survey line. The horizontal offsets between SOVs and wells ranges about 60 m to 3,200 m. The single vintage of source excitation takes about 3 hours for 60 sweeps. The upgoing reflected and/or refracted waves from lithological boundaries were clearly captured even in the maximum offset of 3,200 m. This result suggested that permanent deployment of seismic sources and receivers could be a cost-effective tool for CO2 plume monitoring on commercial-scale geological carbon storages.
Data quality of SOVs-DAS acquisitions is one of key factors to be considered for time-lapse seismic monitoring of CO2 plume. The energy of SOV’s single sweep is much weaker than a single sweep by a vibroseis truck. The walk-away VSP (vertical seismic profiling) imaging can improve the signal-to-noise ratio with stacking multiple data swept at multiple source points, while offset VSP imaging from a single source point by SOVs can be improved only by increasing of number of vertical stacks.
To optimize acquisition parameters, we analysed the baseline survey data from SOV-DAS acquisition at CCS project in ND, USA. The four installations of SOVs and two wells (injection and observation wells) are aligned as a 2D survey line. The horizontal offsets between SOVs and wells ranges about 60 m to 3,200 m. The single vintage of source excitation takes about 3 hours for 60 sweeps. The upgoing reflected and/or refracted waves from lithological boundaries were clearly captured even in the maximum offset of 3,200 m. This result suggested that permanent deployment of seismic sources and receivers could be a cost-effective tool for CO2 plume monitoring on commercial-scale geological carbon storages.