Tomographic waveform inversion with wave-field decomposition
Li Zhiye1,2, Li Zhenchun1, Liu Yujin1, Zhang Kai1
1. School of Geosciences, China University of Petroleum(East China), Qingdao, Shandong 266580, China;
2. Research Institute of CNOOC, Shenzhen Ltd., Shenzhen, Guangdong 518000, China
Abstract:Full waveform inversion is an important approach to rebuild subsurface model with all the information of seismic data. However conventional full waveform inversion can only recover short wavelength component of subsurface model when seismic data is lack of low frequency and long offset information. In this paper, we propose an approach to improve the long wavelength updates of full waveform inversion, which uses gradient separation and recombination. This approach decomposes the FWI gradient into a tomographic term and a migration term. The tomographic term obtained by cross correlating wave-field traveling in similar directions, mainly updates the long wavelengths of the model parameters. The migration term obtained by cross correlating wave-field traveling in opposite directions, mainly updates the short wavelengths of the model parameters. We use Poynting vectors to decompose wave fields and separate gradient. After recombining these two terms, we can achieve a new gradient with a higher weight on the tomographic component. Model test shows that the proposed tomographic waveform inversion with wave-field decomposition can converge to the correct model when conventional FWI fails to do it.
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