Time-lapse FWI for reservoir monitoring in sub-chalk and superimposed reservoirs

Time-lapse seismic monitoring is used in the oil and gas industry to estimate the subsurface property variations associated with reservoir changes during production. In comparison to the conventional 4D approach, requiring processing and imaging of base and monitor data to derive the 4D signal, time-lapse full-waveform inversion (FWI) allows for the direct measurement of the velocity variations. Here, we discuss how the time-lapse FWI flow is applied to capture reservoir changes in complex geological settings. We show results from two case studies: the first is characterized by a 4D anomaly as weak as 1% over a dipping reservoir in the North Sea; the second is in a context of superimposed reservoirs in West Africa. The results obtained by applying this technology show that time-lapse FWI is a valuable monitoring tool in cases of complex geology or sparse acquisitions.