Amplitude-preserving reverse time migration: From reflectivity to velocity and impedance inversion

Abstract

Conventional methods of prestack depth imaging aim at producing a structural image that delineates the interfaces of the geologic variations or the reflectivity of the earth. However, it is the underlying impedance and velocity changes that generate this reflectivity that are of more interest for characterizing the reservoir. Indeed, the need to generate a better product for geologic interpretation leads to the subsequent application of traditional seismic-inversion techniques to the reflectivity sections that come from typical depth-imaging processes. The drawback here is that these seismic-inversion techniques use additional information, e.g., from well logs or velocity models, to fill the low frequencies missing in traditional seismic data due to the free-surface ghost in marine acquisition. We found that with the help of broadband acquisition and processing techniques, the bandwidth gap between the depth-imaging world and seismic inversion world is reducing. We outlined a theory that shows how angle-domain common-image gathers produced by an amplitude-preserving reverse time migration can estimate impedance and velocity perturbations. The near-angle stacked image provides the impedance perturbation estimate whereas the far-angle image can be used to estimate the velocity perturbation. In the context of marine acquisition and exploration, our method can, together with a ghost compensation technique, be a useful tool for seismic inversion, and it is also adaptable to a full-waveform inversion framework. We developed synthetic and real data examples to test that the method is reliable and provides additional information for interpreting geologic structures and rock properties.

Directional‐oriented wavefield imaging: a new wave‐based subsurface illumination imaging condition for reverse time migration

“…; Zhang et al . ). Figure (b) shows samples of weighting functions computed at four different depth locations.…”

“…depth point at crossline location were calculated using equation (17). Seismic events located in 0°-5°were excluded in the calculation of DOWFI because of the singularity problem in the amplitude-preserving RTM (Xu et al 2011;Zhang et al 2014). Figure 4(b) shows samples of weighting functions computed at four different depth locations.…”

Salt-related structure geologic model of Pre-Caspian Basin and analysis on imaging capability

“…In which, h is the reflection angle at the imaging location and the term d(h 0 (x; x s ) -h) represents the conversion from shot gathers to reflection angle gathers (Zhang et al 2014). Therefore, in the future, we suggest adopt the anisotropic method and amplitude-preserving crosscorrelation imaging condition to obtain the ADCIGs and more precisely imaging results.…”

“…At last, the similar correlation-type imaging condition is employed to obtain the image (Zhang et al 2014),…”

Multiscale phase inversion for 3D ocean‐bottom cable data

“…To speed up convergence, approximations to the inverse Hessian can be used (Pratt et al 1998;Métivier et al 2012;Feng, Guo and Schuster 2018). Qin, Allemand and Lambaré (2015) and Tang and McMechan (2017) use amplitude-preserving reverse time migration (Zhang et al 2014) for calculating the FWI gradient. Plessix and Li (2013) suggest that after source deconvolution/whitening of the data, a spectral shaping of ω − β/2 (β = 1 for 3D and 2 for 2D) is applied to the data so that the spectrum of the FWI gradient is similar to the Earth spectrum.…”