From Full Waveform Inversion to Kirchhoff Least-Squares Migration – Correcting the Effects of Mass-Transport Complexes for Better Reservoir Imaging

Complex overburden geology often creates difficulties for imaging any underlying reservoir. One such example is the thick layers of mass-transport complexes (MTCs) below the seabed in a Gulf of Mexico study area. The presence of MTCs poses two main imaging issues. One is the kinematic error due to the unresolved rapid lateral velocity changes from highly-variable, small-scale internal structures within the MTCs. The other imaging issue is uneven illumination resulting from seismic waves passing through the inhomogeneities within the MTCs. We utilized full waveform inversion (FWI) to derive a high-resolution velocity model within the MTCs and then kinematically restored the structural positions of underlying events through Kirchhoff depth migration. This procedure did not correct the amplitude distortion at the reservoir level due to uneven illumination. Utilizing the velocity model derived from FWI, we were able to model the amplitude distortion in the recorded data and compensated for the energy lost due to uneven illumination through the process of Kirchhoff least-squares migration (LSM). With the combination of FWI and LSM, both structural integrity and amplitude fidelity of the image of the deep reservoir horizon were improved.