Seismic differential semblance-oriented Migration Velocity Analysis status and way forward
Hervé Chauris, Milad Farshad- Geochemistry and Petrology
- Geophysics
Differential Semblance Optimization (DSO) is a seismic waveform inversion approach. It has been proposed to remove the limitation of conventional full waveform inversion as a velocity model building tool when only reflected waves are available. It has connections with Migration Velocity Analysis (MVA) techniques defined in the image domain to build macro velocity models, with a splitting between the macro-model and the small-scale heterogeneities. Among the various DSO approaches, DSO-MVA has unique characteristics for complex velocity model building, while ensuring the convergence to the global minimum in a local optimization approach: the wavefields are computed with the two-way wave equation operators, focusing panels are built in a survey-sinking mode and the quality of the macro velocity model is evaluated on common image gathers in the subsurface offset domain through a differential annihilator. We review here the significant aspects that have been better understood over the last fifteen years and discuss the way forward. A first identified issue has been the imprint of the small-scale heterogeneities on the macro-model update that was revealed with the use of wave-equation based Green's functions and an ad-hoc solution was later proposed by slightly modifying the definition of the objective function. A second important aspect has been the development of efficient approaches to compute the required quantitative migration based on approximate inverses to replace the previously used migrations. The issue of correctly interpreting the amplitudes has also moved into one of an improved model parameterization, i.e. from constant-density acoustics media to full acoustic media as a path towards fully visco-elastic media. Finally, we discuss the way forward with the challenges of extending DSO-MVA beyond the single scattering approximation, for processing diving waves and multiples, but also the challenge of the numerical implementation, that remains critical even in 2D, for an applicability on large-scale real data.