Time-lapse wireline DAS-VSP field experiment using an existing onshore well in Japan

We conducted a time-lapse wireline Distributed Acoustic Sensing (DAS)-VSP field experiment in 2022 and 2023 using an existing well in a depleted onshore oil field in Japan. An optic fiber cable was deployed in the same way as wireline logging, and we evaluated its quality and effectiveness for time-lapse applications. Surface seismic data were also acquired for comparison. Surprisingly, the acquired DAS-VSP data exhibited a high signal-to-noise ratio (S/N), which was not expected based on our prior small-scale DAS-VSP test. For the time-lapse survey, the fiber cable was retrieved between the two surveys but was deployed each year. This resulted in a depth variation of a few meter differences between surveys, but this non-repeatability could be corrected during data processing. Final imaging results were compared with surface seismic data, showing that DAS-VSP exhibited high repeatability and higher resolution, indicating the potential of wireline DAS-VSP for time-lapse surveys. Although permanent fiber-optic cable deployment is the ideal choice for long-term monitoring, our results suggest that wireline DAS-VSP can serve as a viable alternative. The result opens possibilities for time-lapse wireline DAS-VSP applications in the fields such as CCS and geothermal reservoir monitoring.