Investigation on Optimal Walkaway Vsp Survey for Reservoir Monitoring with Fwi in Abu Dhabi

Summary Application of FWI to time-lapse borehole seismic data has the potential to be a powerful solution for the successful CO2-EOR reservoir monitoring. A previous study applied acoustic FWI to the field data of time-lapse walkaway VSP acquired in Abu Dhabi. Their FWI study obtained an accurate velocity model of the baseline data with quite high resolution. In this paper, we reviewed the time-lapse FWI results for the field data. After that, we investigated an appropriate acquisition geometry and feasible timing of monitoring surveys through time-lapse velocity model building assuming CO2-EOR and a synthetic FWI study. As a result of the time-lapse FWI for the field data, 4D signals were not captured, even with the high repeatability between the baseline and monitoring data, due to the quite small amount of fluid volume injected between the surveys. As for the synthetic FWI study, we confirmed that extending receivers upward contributed to the extension of imaging area outward. On the other hand, from the monitoring perspective, deploying the receivers both above and below the target reservoir was recommended. Without the receivers below the reservoir, we found that target-oriented time-lapse FWI was effective.