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Research and Application of Common Reflection Surface Stack and Its Attributes in Seismic Data Processing

Author: ZuoTian
Tutor: WangYanChun
School: Chinese Geology University (Beijing)
Course: Geophysical Engineering
Keywords: common reflection surface stack signal-to-noise ratio kinematic wavefield attributes velocity inversion residual static corrections
CLC: P631.4
Type: PhD thesis
Year: 2007
Downloads: 300
Quote: 4
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Abstract


Zero-offset (ZO) section is an important intermediate result in seismic reflection imaging. Common-midpoint (CMP) stack, normal-moveout correction/dip-moveout correction/stack(NMO/DMO/stack), as well as pre-stack migration are the main methods to obtain zero-offset section in conventional seismic processing. These conventional methods require macro-velocity model of subsurface and, the image quality are depended on the accuracy of the velocity model. In the eighties of last century, new stacking techniques have been established which yield better stacking results than the conventional methods mentioned above. They used several kinematic wavefield attributes instead of only one in NMO/DMO/stack. On behalf of the new type of multi-coverage method, the common reflection surface (CRS), which developed by Prof. Hubral of Karlsurhe university in Germany, has been widely accepted by geophysicists.Common reflection surface stack is a macro-model independent seismic imaging method and takes also the local curvature of the reflector at the reflection point into account. Based on the similarity of common reflection point(CRP) trace gathers in one coherent zone (Fresnel zone), CRS stack effectively improves S/N ratio by using more CMP trace gathers to stack. Compared with conventional CMP stack and DMO stack , CRS stack can focus more energy in the vicinity of the reflector. It not only improves the quality of simulated zero-offset section and S/N ratio in deeper layers but also provides important seismic three-parameters section which can be used for inversion of a macro-velocity model and for depth image. It is regarded as one important method of seismic data processing.In this paper, we have studied several forward and inverse problems by means of CRS stack and its kinematic wavefield attributes.Firstly, we developed several methods to reconstruct macro-velocity model in 2D seismic datasets. The CRS stack makes full use of the multi-coverage seismic reflection data and provides additional traveltime parameters. These parameters are very useful for the extraction of further attributes of the seismic medium or for an inversion of a meaningful subsurface velocity model. We can obtain three kinematic wavefield attributes through 2D CRS stacking. These attributes, expressed in terms of wavefront curvatures and emergence angle, can be combined to estimate the RMS velocities and/or interval velocities within the illuminated part of the subsurface model.Secondly, a new residual static correction approach by means of CRS attributes is presented. We considered to make use of the CRS stack which provides additional information about the subsurface by means of kinematic wavefield attributes. The new approach uses the CRS attributes for the moveout correction and the CRS stacked ZO traces as pilot traces. The result of the cross correlation of each pre-stack trace with the pilot trace is assigned to the corresponding source and receiver locations. This new approach is based on the stack power maximization method. In general, the maximum of this cross correlation stack corresponds to the surfaceconsistent residual static time shift of the respective source or receiver. Thus, one of the advantages of this method is that it makes use of more information of the seismic multi-coverage reflection data.Finally, we combined velocity inversion by means of CRS attributes with prestack migration to establish initial macro-velocity model, replacing the conventional velocity analysis and a Dix inversion in a seismic processing routine. The obtained velocity model can be used in a subsequent prestack migration or post-stack migration to determine a depth/time domain image of the subsurface. Otherwise, the projected Fresnel zone based on the kinematic wavefield attributes can be used to to determine an optimal migration aperture in Kirchhoff migration. As is shown, not only the prestack depth migration but also the poststack migration benefits from this approach.Application of the comprehensive processing methods by means of CRS on synthetic examples and field seismic records, the results of these methods show an excellent performance of the algorithm both in accuracy and efficiency. They can provide high accuracy of the velocity model for AVO, and improve the quality of velocity spectra, enhance the continuity of reflection events and the signal-to-noise (S/N) ratio after stacking.

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CLC: > Astronomy,Earth Sciences > Geology > Geology, mineral prospecting and exploration > Geophysical exploration > Seismic exploration
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