Acquisition aperture correction in angle‐domain and true‐amplitude imaging for wave equation migration

Energy-angle distributions in the local image matrix, which is a function of local incident and receiving angles at a subsurface point, are different for a planar reflector and a diffraction point. The former exhibits a linear distribution along a certain dip direction, whereas the latter shows a scattered distribution in the entire matrix. Therefore, the singular values of the local image matrix in the local angle domain indicate the energy distribution along different dip directions. The difference between the auto-and crosscorrelation coefficients of the sets of singular values between adjacent image points can be used to distinguish these two types of targets and obtain prestack images which contain only diffraction points. Using three synthetic examples, we found that the method can effectively image diffraction points. Seismic images of diffraction points may provide important information about geological discontinuities and diffraction points can be taken as secondary sources for potential applications in imaging subsalt structures which are poorly illuminated by primary waves.

Section: Discussionmentioning

confidence: 99%

Section: Diffraction Points Imaging S3mentioning

confidence: 99%

Imaging diffraction points using the local image matrices generated in prestack migration

Zhu

2010

“…It is also possible to compute ADCIGs by directly decomposing the wavefields in the subsurface into their local directional components (Soubaras, 2003;Wu et al, 2004). So far, this work has been performed on 2D or 3D isotropic migration algorithms, and it produces ADCIGs only in the reflection angle (no azimuth).…”

Section: Introductionmentioning

confidence: 99%

3D angle gathers from reverse time migration

Xu¹,

Zhang²,

Tang³

2011

232

Common-image gathers are an important output of prestack depth migration. They provide information needed for velocity model building and amplitude and phase information for subsurface attribute interpretation. Conventionally, common-image gathers are computed using Kirchhoff migration on commonoffset/azimuth data volumes. When geologic structures are complex and strong contrasts exist in the velocity model, the complicated wave behaviors will create migration artifacts in the image gathers. As long as the gather output traces are indexed by any surface attribute, such as source location, receiver location, or surface plane-wave direction, they suffer from the migration artifacts caused by multiple raypaths. These problems have been addressed in a significant amount of work, resulting in common-image gathers computed in the reflection angle domain, whose traces are indexed by the subsurface reflection angle and/or the subsurface azimuth angle.Most of these efforts have concentrated on Kirchhoff and oneway wave-equation migration methods. For reverse time migration, subsurface angle gathers can be produced using the same approach as that used for one-way wave-equation migration. However, these approaches need to be revisited when producing high-quality subsurface angle gathers in three dimensions (reflection angle/azimuth angle), especially for wide-azimuth data. We have developed a method for obtaining 3D subsurface reflection angle/azimuth angle common-image gathers specifically for the amplitude-preserved reverse time migration. The method builds image gathers with a highdimensional convolution of wavefields in the wavenumber domain. We have found a windowed antileakage Fourier transform method that leads to an efficient and practical implementation. This approach has generated high-resolution angle-domain gathers on synthetic 2.5D data and 3D wideazimuth real data.

“…It has many applications, including survey design ͑e.g., Li and Dong, 2006͒, studying the influences of acquisition geometry and overburden structures on the image ͑e.g., Jin and Walraven, 2003;Wu and Chen, 2006;Xie et al, 2006͒, and image amplitude correction ͑e.g., Wu et al, 2004;Wu, 2005, 2008͒. Traditionally, illumination analyses have used ray-based methods ͑e.g., Schneider and Winbow, 1999;Bear et al, 2000;Muerdter et al, 2001;Ratcliff, 2001a, 2001b;Lecomte et al, 2003͒, in which the directional information is inherently carried by the rays. However, the high-frequency asymptotic approximation and the caustics inherent in ray theory might limit severely its accuracy in complex regions ͑e.g., Hoffmann, 2001͒.…”

Section: Introductionmentioning

confidence: 99%

Full-wave directional illumination analysis in the frequency domain

Cao

2009

Directional illumination analysis based on one-way wave equations has been studied extensively; however, its inherent limitations, e.g., one-way propagation, wide-angle error, and amplitude inaccuracy, can severely hinder its applications for accurate survey design and true-reflection imaging corrections in complex media. We have analyzed the illumination in the frequency domain using full two-way wave propagators considering the extensive computation and huge storage required for time-domain methods, and the fact that the illumination is frequency dependent. This full-wave analysis can provide frequency-dependent full-angle true-amplitude illumination not only for the downgoing waves but also for the upgoing waves, including turning waves and reflected waves. Two methods were considered to decompose the full wavefield into the local angle domain: a direct full-dimensional decomposition and more efficient split-step decomposition composed of three lower-dimensional decompositions.The results of illumination analysis demonstrated the advantages of this method. The two decomposition methods produced similar results.