Improved direct envelope inversion and structure-guided perturbation decomposition for salt building

Abstract

Summary Salt velocity building is a difficult task for conventional full waveform inversion (FWI) if there is not enough low-frequency data and prior information. The direct envelope inversion (DEI) method is quite effective for salt building in the case of seismic data lacks low-frequency information. However, in the current DEI studies, the calculation of the envelope-filed, which needs nonlinear envelope operator, does not consider the influences of wavefield overlapping, and the inversion quality of subsalt areas needs further improvements. In this paper, we analyze the effects of wavefield overlapping on the envelope-field calculation and propose a new envelope-field calculation method. Based on this, we propose a wavefield decomposition based direct envelope inversion (WDDEI) method, in which the gradient is calculated using the new envelope-field. To improve the inversion effects of subsalt structures, we propose a structure-guided perturbation decomposition method, which can separate the strong scattering salt information from the DEI result with the help of reverse time migration image. Finally, numerical tests are conducted on a modified SEG/EAGE salt model to demonstrate the effectiveness of the proposed method.