A practical approach to P‐SV prestack time migration and velocity analysis for transverse isotropy

Geophysical Prospecting

Mancini

2007

SUMMARYCommon-conversion-point binning associated with converted-wave (C-wave) processing complicates the task of parameter estimation, especially in anisotropic media. To overcome this problem, we derive new expressions for converted-wave prestack time migration (PSTM) in anisotropic media and illustrate their applications using both 2D and 3D data examples.The converted-wave kinematic response in inhomogeneous media with vertical transverse isotropy (VTI) is separated into two parts: the response in horizontally layered VTI media and the response from a point scatter. The former controls the stacking process and the latter controls the process of PSTM. The C-wave traveltime in horizontally layered VTI media is determined by four parameters: the C-wave stacking velocity V C2 , the vertical and effective velocity ratios γ 0 and γ eff , and the C-wave anisotropic parameter χ eff . These four parameters are referred to as the C-wave stacking velocity model. In contrast, the C-wave diffraction time from a point scatter is determined by five parameters: γ 0 , V P2 , V S2 , η eff and ζ eff , where η eff and ζ eff are, respectively, the P-and S-wave anisotropic parameters, and V P2 and V S2 are the corresponding stacking velocities. V P2 , V S2 , η eff and ζ eff are referred to as the C-wave PSTM velocity model. There is a one-to-one analytical link between the stacking velocity model and the PSTM velocity model. There is also a simple analytic link between the C-wave stacking velocities V C2 and the migration velocity V Cmig , which is in turn linked to V P2 and V S2 .Based on the above, we have developed an interactive processing scheme to build the stacking and PSTM velocity model and to perform 2D and 3D C-wave anisotropic PSTM.Real data applications show that the PSTM scheme substantially improves the quality of Cwave imaging compared with the DMO (dip moveout) scheme, and these improvements have been confirmed by drilling.

Section: Introductionmentioning

confidence: 99%

Converted‐wave imaging in anisotropic media: theory and case studies

Geophysical Prospecting

Mancini

2007

“…However, anisotropic CCP binning and converted-wave DMO is strongly velocity-dependent and this severely limited the success of this approach. Since 1999, efforts have also been made to develop converted-wave anisotropic PSTM to replace the CCP-binning and DMO approach (e.g., Li and Druzhinin, 2000;Dai and Li 2001;Dai, 2003;amongst others). Here, we review these developments and present a unified and interactive approach for converted-wave imaging and parameter estimation in anisotropic media.…”

Section: Introductionmentioning

confidence: 99%

Converted‐wave imaging in anisotropic media: An overview

SEG Technical Program Expanded Abstracts 2004

Mancini

2004

Self Cite

This paper reviews the recent developments in convertedwave (C-wave) processing for vertical transverse isotropy (VTI), and addresses issues such as how many parameters are required to perform C-wave anisotropic prestack time migration (PSTM), and how to estimate these parameters. Both recent 2D and 3D data examples will be used to illustrate these developments. The converted-wave kinematic response in inhomogeneous VTI media is separated into two parts: the zero-dip response for horizontally layered VTI media and the all dip response from a point scatter. The former controls the stacking process and the latter controls the process of PSTM. The C-wave traveltime in horizontally layered VTI media is determined by four parameters: the C-wave stacking velocity V C2 , the vertical and effective velocity ratios γ 0 and γ eff , and the C-wave anisotropic parameter χ eff. These four parameters are referred to as the C-wave stacking velocity model. In contrast, the C-wave diffraction time from a point scatter is determined by five parameters: γ 0 , V P2 , V S2 , η eff and ζ eff , where η eff and ζ eff are, respectively, the P-and S-wave anisotropic parameters, and V P2 and V S2 are the corresponding stacking velocities. V P2 , V S2 , η eff and ζ eff are referred to as the C-wave PSTM velocity model. There is a one-to-one analytical link between the stacking velocity model and the PSTM velocity model. Based on the above understanding, we have developed an interactive processing scheme to build the stacking and PSTM velocity model and to perform 2D and 3D C-wave anisotropic PSTM. Real data applications show that the PSTM scheme substantially improves the quality of Cwave imaging compared with the DMO scheme, and these improvements have been confirmed by drilling.

“…To address these issues, we derive an anisotropic doublesquare-root (DSR) equation for a scatter point located beneath a stack of VTI layers, and incorporate it into prestack migration. This is an extension of Li and Druzhinin (2000) in which a single-layer DSR equation is used and is thus restricted to homogeneous media. The new DSR equation is valid for vertically inhomogeneous anisotropic media, and is fully determined by five parameters which can be estimated from non-hyperbolic moveout analysis.…”

Section: Introductionmentioning

confidence: 99%

Anisotropic migration and model building for 4C seismic data: A case study from Alba

SEG Technical Program Expanded Abstracts 2001

2001

Self Cite

Assuming a scatter point located beneath a stack of layers with vertical transverse isotropy (VTI), we derive an accurate double-square-root (DSR) converted-wave (Cwave) diffraction equation, and incorporate the equation into the Kirchhoff prestack time migration. The DSR is controlled by five parameters: P-and S-wave stacking velocities V P2 and V S2 , vertical velocity ratio g 0 , and anisotropic parameters h eff and z eff , which define the anisotropic velocity model for migration. We demonstrate using real data how to build the anisotropic model from reflection moveout analysis, and evaluate the merit of prestack time migration. The DSR equation has a similar form to its isotropic counterpart, which allows an efficient implementation of prestack time migration. Applications to real data show that the C-wave imaging obtained by the new approach is more focused and coherent than the imaging by isotropic methods.