Focused monitoring using Vertical Seismic Profile data

Recent developments in light and ultra-light monitoring methods have made it possible to focus on specific “spot” locations using light seismic spreads and tailored processing workflows for both onshore and offshore surveys. This paper shows how the procedure has been adapted to VSP data. VSP data recorded with an optical fiber and a DAS system can be successfully used for focussed seismic monitoring. A conventional VSP processing sequence is applied to a DAS-VSP dataset acquired for CO2 injection monitoring. The corridor-stacked VSP traces are compared with synthetic seismograms, and a stratigraphic deconvolution process is used to match the corridor stacks to the synthetics. The efficiency of the workflow is assessed through correlation and NRMS metrics. The monitoring procedure has been fully automated, both in data processing and in the detection of CO2 using seismic attributes—specifically through the computation of a residual time-shift curve combined with differential instantaneous-amplitude criteria.