Characterizing the target of interest underlying a complex overburden with target-oriented elastic waveform inversion

Abstract

It remains challenging for elastic full waveform inversion (EFWI) to characterize the elastic properties of a target reservoir deep beneath complex overburden media. This can be attributed to two factors. 1) The complex wavefield distortions arising from the overburden obscure the target reflection properties, resulting in a target zone with limited energy illumination. 2) High-resolution EFWI for the whole inversion domain is computationally expensive. To overcome these challenges, instead of directly inverting for the subsurface model using surface seismic data, we develop a target-oriented elastic waveform inversion scheme. We first retrieve the elastic reflection response to the target zone of interest by projecting seismic data from surface to the datum level. Then, we can apply high-resolution EFWI on the target zone by using the retrieved elastic reflection data. To better handle the complex overburden, which may include anisotropy and salt bodies, we make full use of the prior estimate of the overburden in the redatuming process to obtain a reliable reflection response to the target zone. In the numerical examples, we use the SEAM model with an anisotropic overburden and a salt body model to demonstrate the feasibility and effectiveness of the proposed method and analyze the influence of anisotropy and high-contrast salt in the overburden on the redatuming and inversion results, respectively.