Observations of Time-Lapse Converted-Wave Anomalies on Valhall LoFS Data

We analyse a subset of the converted-wave data from the Valhall LoFS surveys 1 and 3 in order to investigate whether any time-lapse signal can be seen on the converted waves. Measurements of shear-wave splitting indicate a change in the magnitude of azimuthal anisotropy in the overburden between the surveys. After PSTM we observe a significant time-lapse anomaly at the reservoir level at the location of a production well. The anomaly is only found for azimuth sectors around the average polarization direction of the slow shear wave in the reservoir interval.