The Experts below are selected from a list of 16971 Experts worldwide ranked by ideXlab platform

D Longstaff - One of the best experts on this subject based on the ideXlab platform.

A Gunawardena - One of the best experts on this subject based on the ideXlab platform.

W A Mulder - One of the best experts on this subject based on the ideXlab platform.

  • Seismic attenuation imaging with causality
    Geophysical Journal International, 2011
    Co-Authors: Bobby Hak, W A Mulder
    Abstract:

    Seismic data enable imaging of the Earth, not only of velocity and density but also of attenuation contrasts. Unfortunately, the Born approximation of the constant-density visco-acoustic wave equation, which can serve as a forward modelling operator related to Seismic Migration, exhibits an ambiguity when attenuation is included. Different scattering models involving velocity and attenuation perturbations may provide nearly identical data. This result was obtained earlier for scatterers that did not contain a correction term for causality. Such a term leads to dispersion when considering a range of frequencies. We demonstrate that with this term, linearized inversion or iterative Migration will almost, but not fully, remove the ambiguity. We also investigate if attenuation imaging suffers from the same ambiguity when using non-linear or full waveform inversion. A numerical experiment shows that non-linear inversion with causality convergences to the true model, whereas without causality, a substantial difference with the true model remains even after a very large number of iterations. For both linearized and non-linear inversion, the initial update in a gradient-based optimization scheme that minimizes the difference between modelled and observed data is still affected by the ambiguity and does not provide a good result. This first update corresponds to a classic Migration operation. In our numerical experiments, the reconstructed model started to approximate the true model only after a large number of iterations.

Zhaoqi Gao - One of the best experts on this subject based on the ideXlab platform.

  • enhancing subsurface scatters using reflection damped plane wave least squares reverse time Migration
    IEEE Geoscience and Remote Sensing Letters, 2020
    Co-Authors: Jinghuai Gao, Rongrong Wang, Zhaoqi Gao
    Abstract:

    Subsurface scatters are sometimes masked by reflectors in Seismic Migration images, because the diffractions are much weaker in energy than the reflections. We propose a novel imaging method, named reflection-damped plane-wave least-squares reverse time Migration (RD_PLSRTM), to enhance the scatters in the Migration image. We formulate Seismic imaging as an inverse problem that minimizes a weighted residual between the modeled and observed Seismic data. In the proposed approach, we use the plane-wave destruction filter to separate the diffractions from the reflections in the data residual. A reflection-damped weighting matrix is then used to govern the fitting of the diffractions and the reflections, and therefore emphasize the updates of the scatters. The inverse problem is finally solved by using an iteratively reweighted least-squares (IRLS) algorithm. The proposed method provides a generalized formulation that could be reduced to conventional PLSRTM and PLSRTM of diffractions (PLSRTM_D) by using specific damping factors. We conduct imaging tests on synthetic and field data that prove the superiority of the proposed method over PLSRTM in imaging deep scatters and subsalt scatters. Compared with PLSRTM_D, it could produce high-quality images of not only the scatters but also the reflectors.

Tieyuan Zhu - One of the best experts on this subject based on the ideXlab platform.

  • Time-reverse modelling of acoustic wave propagation in attenuating media
    Geophysical Journal International, 2014
    Co-Authors: Tieyuan Zhu
    Abstract:

    Time-reverse modelling (TRM) of acoustic wave propagation has been widely implemented in Seismic Migration and time-reversal source imaging. The basic assumption of this modelling is that the wave equation is time-invariant in non-attenuating media. In the Earth, attenuation often invalidates this assumption of time-invariance. To overcome this problem, I propose a TRM approach that compensates for attenuation and dispersion effects during the wave propagation in attenuating media. This approach is based on a viscoacoustic wave equation which explicitly separates attenuation and dispersion following a constant-Q model. Compensating for attenuation and dispersion during TRM is achieved by reversing the sign of the attenuation operator coefficient while leaving the counterpart dispersion parameter unchanged in this viscoacoustic wave equation. A low-pass filter is included to avoid amplifying high-frequency noise during TRM. I demonstrate the effects of the filter on the attenuation and the phase velocity by comparing with theoretical solutions in a 1-D Pierre shale homogeneous medium. Three synthetic examples are used to demonstrate the feasibility of attenuation compensation during TRM. The first example uses a 1-D homogeneous model to demonstrate the accuracy of the numerical implementation of the methodology. The second example shows the applicability of source location using a 2-D layering model. The last example uses a 2-D cross-well synthetic experiment to show that the methodology can also be implemented in conjunction with reverse-time Migration to image subsurface reflectors. When attenuation compensation is included, I find improved estimation of the source location, the excitation timing of the point source, the magnitude of the focused source wavelet and the reflectivity image of reflectors, particularly for deep structures underneath strongly attenuating zones.