Broadband seismic and FWI to resolve an incised shallow carbonate platform, Indonesia

Full Waveform Inversion (FWI) has become an important tool to resolve velocity anomalies, especially in shallow water environments, where the limitation in offset and/or angle range creates uncertainty for velocity model updating using travel-time reflection tomography. In a newly acquired 3D broadband seismic survey, offshore North Madura, Indonesia, shallow gas channels and eroded carbonate platforms lead to uncertainty in accurately interpreting structures and lithologies. Starting from a simple velocity model, the combined use of FWI and ray-traced reflection tomography can address the localized velocity challenges and allow the imaging algorithm to correctly position deeper plays. A significant advantage of broadband seismic data for velocity model building is its ability to generate useable low frequency input for FWI. This can relax the constraint on the starting models accuracy by mitigating cycle-skipping. A detailed shallow velocity model conforming to the geology can be derived from this process while conventional reflection tomography remains well suited for model updating in the deeper section. Corrections of small-scale velocity anomalies in the shallow part of the velocity model bring structural uplift in the reservoir plays which include Miocene carbonates and syn-rift Eocene clastic systems.