Abstract
In conventional full-waveform inversion (FWI), viscous effects are typically neglected, and this is likely to adversely affect the recovery of P-wave velocity. We have developed a strategy to mitigate viscous effects based on the use of matching filters with the aim of improving the performance of acoustic FWI. The approach requires an approximate estimate of the intrinsic attenuation model, and it is one to three times more expensive than conventional acoustic FWI. First, we perform 2D synthetic tests to study the impact of viscoacoustic effects on the recorded wavefield and analyze how that affects the recovered velocity models after acoustic FWI. Then, we apply the current method on the generated data and determine that it mitigates viscous effects successfully even in the presence of noise. We find that having an approximate estimate for intrinsic attenuation, even when these effects are strong, leads to improvements in resolution and a more accurate recovery of the P-wave velocity. Then, we implement and develop our method on a 2D field data set using Gabor transforms to obtain an approximate intrinsic attenuation model and inversion frequencies of up to 24 Hz. The analysis of the results indicates that there is an improvement in terms of resolution and continuity of the layers on the recovered P-wave velocity model, leading to an improved flattening of gathers and a closer match of the inverted velocity model with the migrated seismic data.
Highlights
As seismic waves travel through the subsurface, the media in which they travel absorb part of their energy due to the inherent viscosity
The second difference is due to the fact that elastic effects are not considered and because an approximate Q model can be obtained directly from reflection data without having to perform any inversion. We demonstrate that such an approximate Q model is enough to mitigate most of the viscoacoustic effects from the data, leading to improved P-wave velocity models
If these phenomena are not included in the constitutive law when carrying out full-waveform inversion (FWI), the wavefield is computed with errors and these translate into inaccuracies in the inverted velocity models
Summary
As seismic waves travel through the subsurface, the media in which they travel absorb part of their energy due to the inherent viscosity. In the past few decades, FWI has had some success in obtaining high-resolution and accurate velocity models, as well as smooth intrinsic attenuation models of the subsurface, despite its ill-posed nature. With this aim, several authors have implemented viscoacoustic FWI in the frequency domain, in which viscous effects are incorporated in seismic modeling by introducing intrinsic attenuation as the imaginary component of P-wave velocity (Pratt, 1990, 1999; Pratt and Worthington, 1990; Song et al, 1995; Plessix et al, 2012; Prieux et al, 2013; Operto et al, 2015), whereas others have implemented FWI in the time domain (Cheng et al, 2015; Plessix et al, 2016; Bai et al, 2017). A variety of approaches have been used to recover the intrinsic attenuation, Manuscript received by the Editor 10 January 2018; revised manuscript received 24 May 2018; published ahead of production 26 July 2018; published online 1 October 2018
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