Abstract

The present case study is from the Heera field of Western Offshore Basin, India. In this field, the shallow low velocity anomaly zones cause the velocity pushdown effect which results in pseudo structural sags in the time domain seismic data. Proper depth conversion through advanced imaging techniques may reveal the true structures that are masked in the time domain seismic data. The velocity model derived from the legacy seismic data of Heera field, recorded in 1999, with limited far offset, was not accurate enough to remove the effect of shallow low velocity anomalies from the subsurface image even after anisotropic Pre-Stack Depth Migration (APSDM). These shallow velocity anomalies cause the structural sags even in the deeper sections in anisotropic PSDM image which results in false imprints of low structure bounding faults. Advanced multicomponent seismic data processing, high resolution velocity modeling using Full Waveform Inversion (FWI), PP & PP-PS joint tomography and anisotropic PSDM of recently acquired 4C-3D OBN full azimuth seismic data brought out high resolution sub-surface image as compared to the anisotropic PSDM of limited offset and low fold old seismic data. The imprints of shallow low velocity anomalies, which cause pseudo structures in time domain seismic data, are minimized in OBN 4C-3D depth domain PSDM seismic data.