Elastic FWI of the CAMI FRS 3D walkaway-walkaround VSP fiber survey: a synthetic case study

Matthew Eaid, Scott Keating, Marie Macquet, Kristopher A. Innanen

Distributed acoustic sensing could further enable reservoir monitoring by providing a means of acquiring repeatable seismic surveys. Monitoring during CO₂ sequestration is a key area where advancements in DAS monitoring will be beneficial. The containment and monitoring institute (CaMI) has a Field Research Station designed to explore technologies for this very purpose. In 2018 a baseline 3D walkaway-walkaround VSP was acquired with geophones, straight DAS fiber, and helical DAS fiber. In preparation for inverting this dataset and computing a baseline model for future time-lapse surveys, we examine the inversion of simulated datasets from synthetic models computed from field site well logs. A key component of this study is examination of various elastic model parameterizations and the effect they have on the quality of the inversions. Through our analysis we determine that all of the parameterizations tested produce reasonable inversion results, but a p-impedance, s-impedance, density parameterization appears to be the most robust and is most successful in mitigating cross talk. These baseline inverted models are then used as starting models in an inversion from simulated data from models after 5 years of CO₂ injection. Using data from all three sensors types we are able to invert for the P-wave anomaly induced by injection but struggle to invert for the S-wave and density anomalies.