Nonstretching NMO correction of prestack time-migrated gathers using a matching-pursuit algorithm

Zhang, Bo; Zhang, Kui; Guo, Shuxu; Marfurt, Kurt J.

doi:10.1190/geo2011-0509.1

Cited by 56 publications

(17 citation statements)

References 31 publications

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“…In addition, the reflection hyperbolas' intersection of the seafloor reflection with the flat spot reflection can be observed at approximately 1200 m. Because the maximum NMO stretch usually occurs when some of the reflection hyperbolas intersect one another (Buchholtz, 1972;Shatilo and Aminzadeh, 2000;Zhang et al, 2013), the traces around that offset are often muted; in our case, this offset happens to be close to the critical offset for the flat spot reflections. We conclude that the postcritical seismic data from flat spot reflections in F3 were most likely muted before stacking and excluded from the stacked output.…”

Section: Normal Moveout Stretch and Muting Analysismentioning

confidence: 67%

Tuning of flat spots with overlying bright spots, dim spots, and polarity reversals

2015

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Reflection seismic data from block F3 in the Dutch North Sea exhibit many large-amplitude reflections at shallow horizons typically categorized as bright spots. In most cases, these bright reflections show a significant "flatness" that contrasts with local structural trends. Although flat spots in thick reservoirs are often easily identified, others within thin beds or near reservoir edges can be difficult to identify and are poorly understood. Many of the shallow large-amplitude reflections in this block are dominated by flat spots. We investigated the tuning effects that such flat spots cause as they interacted with reflections from the top of the reservoir. We first studied the zero-offset "wedge-model" tuning effects of the flat spot with overlying bright spots, dim spots, or polarity reversals. We then expanded that model to examine prestack tuning effects, as well as the results from inclusion of postcritical flat spot reflections in the final stack. We observed that under certain conditions, the reflections could appear to be somewhat flattened bright spots; those conditions might be met frequently in practice, and they should be considered in routine interpretation. In the North Sea case, we concluded that this tuning effect was the primary cause of the brightness and flatness of these reflections.

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Section: Normal Moveout Stretch and Muting Analysismentioning

confidence: 67%

Tuning of flat spots with overlying bright spots, dim spots, and polarity reversals

2015

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“…Muting of large offset not only lowers the stacking power but also reduces Horizon-based velocity analysis U17 information necessary for accurate prestack inversion of shear impedance and density. Zhang et al (2013) develop a waveletbased algorithm named MPNMO (the matching-pursuit-based normal moveout correction) to minimize the stretch at large aperture. Their algorithm first applies reverse NMO correction, which "resqueezes" the migration stretch of the time-migrated gathers and then conducts a wavelet-based NMO correction on the reverse-NMO-corrected gathers.…”

Section: Minimize the Stretch Associated With Far Offsetmentioning

confidence: 99%

“…In this paper, we first extend Toldi's (1989) method by adding interval anellipticity as one of the parameters for the model to perform automatic nonhyperbolic analysis based on user-defined horizons. We then follow Zhang et al (2013) to minimize the stretch at far offset. We apply our technique as a residual velocity analysis workflow to a prestack time-migrated data volume acquired over the Fort Worth Basin (FWB), USA, and show the improvements on the prestack-corrected gathers and final stacked section.…”

Section: Introductionmentioning

confidence: 99%

Horizon-based semiautomated nonhyperbolic velocity analysis

Zhang

Zhao

et al. 2014

GEOPHYSICS

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With higher capacity recording systems, long-offset surveys are becoming common in seismic exploration plays. Long offsets provide leverage against multiples, have greater sensitivity to anisotropy, and are key to accurate inversion for shear impedance and density. There are two main issues associated with preserving the data fidelity contained in the large offsets: (1) nonhyperbolic velocity analysis and (2) mitigating the migration/NMO stretch. Current nonhyperbolic velocity analysis workflows first estimate moveout velocity V nmo based on the offset-limited gathers, then pick an effective anellipticity η eff using the full-offset gathers. Unfortunately, estimating V nmo at small aperture may be inaccurate, with picking errors in V nmo introducing errors in the subsequent analysis of effective anellipticity. We have developed an automated algorithm to simultaneously estimate the nonhyperbolic parameters. Instead of directly seeking an effective stacking model, the algorithm finds an interval model that gives the most powerful stack. The searching procedure for the best interval model was conducted using a direct, global optimization algorithm called differential evolutionary. Next, we applied an antistretch workflow to minimize stretch at a far offset after obtaining the optimal effective model. The automated velocity analysis and antistretch workflow were tested on the data volume acquired over the Fort Worth Basin, USA. The results provided noticeable improvement on the prestack gathers and on the stacked data volume.

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“…The maximum offset is approximately 4200 m, whereas the target Barnett Shale lies at approximately 2100 m depth. Figure 5a shows a representative time-migrated CMP gather after nonstretch processing (Zhang et al, 2013). White arrows indicate the zone with obvious noise spikes.…”

Section: Applicationmentioning

confidence: 99%

Noise suppression of time migrated gathers using prestack structure oriented filtering

Zhang

Lin

Marfurt

2015

SEG Technical Program Expanded Abstracts 2015

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Prestack seismic analysis provides information on rock properties, lithology, fluid content, and the orientation and intensity of anisotropy. However, such analysis demands high-quality seismic data. Unfortunately, noise is always present in seismic data even after careful processing. Noise in the prestack gathers may not only contaminate the seismic image, thereby lowering the quality of seismic interpretation, but it may also bias the seismic prestack inversion for rock properties, such as acoustic-and shear-impedance estimation. Common postmigration data conditioning includes running window median and Radon filters that are applied to the flattened common reflection point gathers. We have combined filters across the offset and azimuth with edge-preserving filters along the structure to construct a true "5D" filter that preserves amplitude, thereby preconditioning the data for subsequent quantitative analysis. We have evaluated our workflow by applying it to a prestack seismic volume acquired over the Fort Worth Basin, TX. The inverted results from the noise-suppressed prestack gathers are more laterally continuous and have higher correlation with well logs when compared with those inverted from conventional time-migrated gathers.

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Nonstretching NMO correction of prestack time-migrated gathers using a matching-pursuit algorithm

Cited by 56 publications

References 31 publications

Tuning of flat spots with overlying bright spots, dim spots, and polarity reversals

Tuning of flat spots with overlying bright spots, dim spots, and polarity reversals

Horizon-based semiautomated nonhyperbolic velocity analysis

Noise suppression of time migrated gathers using prestack structure oriented filtering

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