Abstract
The estimation of the subsurface acoustic impedance (AI) model is an important step of seismic data processing for oil and gas exploration. The full waveform inversion (FWI) is a powerful way to invert the subsurface parameters with surface acquired seismic data. Nevertheless, the strong nonlinear relationship between the seismic data and the subsurface model will cause nonconvergence and unstable problems in practice. To divide the nonlinear inversion into some more linear steps, a 2D AI inversion imaging method is proposed to estimate the broadband AI model based on a broadband reflectivity. Firstly, a novel scheme based on Gaussian beam migration (GBM) is proposed to produce the point spread function (PSF) and conventional image of the subsurface. Then, the broadband reflectivity can be obtained by implementing deconvolution on the image with respect to the calculated PSF. Assuming that the low-wavenumber part of the AI model can be deduced by the background velocity, we implemented the AI inversion imaging scheme by merging the obtained broadband reflectivity as the high-wavenumber part of the AI model and produced a broadband AI result. The developed broadband migration based on GBM as the computational hotspot of the proposed 2D AI inversion imaging includes only two GBM and one Gaussian beam demigraton (Born modeling) processes. Hence, the developed broadband GBM is more efficient than the broadband imaging using the least-squares migrations (LSMs) that require multiple iterations (every iteration includes one Born modeling and one migration process) to minimize the objective function of data residuals. Numerical examples of both synthetic data and field data have demonstrated the validity and application potential of the proposed method.
Highlights
As the consumption of oil and gas resources increases, the target of seismic exploration is shifting from the large-scale structural reservoirs to small-scale stratigraphic reservoirs [1].Acoustic impedance (AI), as a basic physical parameter, is defined as the product of density and velocity, which plays a key role to connect the surface seismic data to the subsurface model [2,3]
We propose an effective AI imaging approach based on a broadband reflectivity imaging profile under the assumption that the background velocity or AI has been obtained by tomography
Study, we focused on the broadband reflectivity under the linear least-squares migrations (LSMs) inversion frame and estimated the broadband AI model by incorporating the background AI model
Summary
As the consumption of oil and gas resources increases, the target of seismic exploration is shifting from the large-scale structural reservoirs to small-scale stratigraphic reservoirs [1]. The least-squares migration (LSM) is a powerful method for seismic imaging of the broadband reflectivity [20,21,22]. The two-way wave-based least-squares reverse time migration (LSRTM) is known as the most accurate imaging method It is known as the most expensive LSM for computation cost [25,26]. We used the PSFs to deconvolve the image of GBM to produce a broadband subsurface reflectivity as the high-wavenumber part of AI model. We implemented the full AI inversion imaging by merging the obtained broadband reflectivity and the low-wavenumber part of AI model that can be derived from background velocity under assumption of constant density
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