15:00 〜 15:15
[HSC06-06] Challenges of offset DAS/VSP imaging towards low-cost long-term 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
Reducing monitoring costs is one of the key factors to enhance implementing industrial-scale geological carbon storages. Iterative seismic surveys are commonly used to capture a range of a CO2 plume in subsurface. Permanent acquisition on both source and receiver sides can reduce the operation/labor costs significantly, and in future, it could be automated for both data collection and data processing. As permanent receivers, the distributed acoustic sensing (DAS) is now widely adopted in energy/environmental sectors. The small dimension of fiber cables increases possibility to install in narrow spaces, like annulus behind a casing pipe. As permanent sources, rotary seismic sources (e.g. surface orbital vibrators) are gradually getting more attention. The selection of source positon is a key issue to maximize the quality of VSP images. Increasing the offsets expands the range of imaging, but data quality becomes lower.
In this presentation, we analyzed the quality of DAS data versus offsets between receivers and sources. The data was acquired at the well of depth of 880 m with the SM fibers cemented behind the casing pipe. The 4 series of geophone array were deployed in the same well as a reference data. As seismic sources, a vertical vibration truck excited at every 200 m along the 2 km survey line. The offsets ranged 50 m to 1350 m.
DAS records were a lower S/N (signal-to-noise ratio) than geophone records as a single sensor. The S/N, however, was improved by source efforts. The number of stacks was about 5 times more at the near offsets, but about 20 times more at the mid offsets, and more stacks were required for the far offsets. This is partly because of the incident angle of the incoming waves. We also analyzed final imaging quality of DAS records, and concluded that the imaging quality of DAS records was higher than that of geophone records.
In this presentation, we analyzed the quality of DAS data versus offsets between receivers and sources. The data was acquired at the well of depth of 880 m with the SM fibers cemented behind the casing pipe. The 4 series of geophone array were deployed in the same well as a reference data. As seismic sources, a vertical vibration truck excited at every 200 m along the 2 km survey line. The offsets ranged 50 m to 1350 m.
DAS records were a lower S/N (signal-to-noise ratio) than geophone records as a single sensor. The S/N, however, was improved by source efforts. The number of stacks was about 5 times more at the near offsets, but about 20 times more at the mid offsets, and more stacks were required for the far offsets. This is partly because of the incident angle of the incoming waves. We also analyzed final imaging quality of DAS records, and concluded that the imaging quality of DAS records was higher than that of geophone records.