Publications

Recent advances in velocity model building (VMB) using Full Waveform Inversion (FWI) have shown promising progress. Meanwhile, tomography continues to play an important complementary role with FWI to obtain optimal solution for VMB. In this case study, the seismic image at the target depth is affected by complex overburden carbonate platforms in the Miocene layers. Pre-stack Depth Migration (PSDM) with FWI was employed to solve the image problem by using refraction and reflection energy. Refraction energy is widely used for FWI but in this case it does not reach deep enough to the bottom of carbonate due to the limitation of the maximum available offset. Hence, reflection energy is included in FWI to extend the velocity update to cover the complex carbonates. It is crucial that a good initial model is available for refraction FWI and conventional tomography. However, in this study, some “blank” zones are still observed after FWI with both refractions and reflections. These are the zones where reflections are weak so FWI and normal tomography have no clear energy for velocity inversion resulting in structural distortion in the deeper target area. Therefore, dip constrained tomography (DCT) is used for correcting the distortion by comparing the distorted structural dips from different offset stacks beneath the overburden anomaly to generate accurate velocity in the “blank” zones. FWI with both refraction and reflection energy gives very high resolution update of the carbonate platforms, which in turn define clear internal structures and sharp edges of the carbonates. DCT makes use of deeper distortion information and updates the carbonate zones where FWI fails. PSDM with integrated velocity update tools gives a more reliable image of the target area.