Estimation of time-lapse velocity change by multi-parameter elastic FWI

In this study, we present a double difference multi-parameter elastic 4D FWI, where elastic properties such as P-wave impedance, P-wave velocity and the Vs/Vp ratio are simultaneously inverted. Multi-parameter FWI allows to separate velocity and impedance effects. In 4D, this ability is key, particularly in a reservoir compaction scenario with a decrease of the overburden and underburden velocities due to extensional stress. These subtle long-wavelength but important changes can be captured with a multi-parameter FWI, whereas the impedance term (or the migration isochron) tends to dominate the model update in a mono-parameter FWI. Using synthetic and real data examples, we demonstrate that for well repeated OBN surveys in deep water, the time-lapse velocity changes are correctly inverted with proposed workflow.