Difference between revisions of "Residual statics corrections"

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Revision as of 13:07, 5 August 2014

Seismic Data Analysis
Series Investigations in Geophysics
Author Öz Yilmaz
DOI http://dx.doi.org/10.1190/1.9781560801580
ISBN ISBN 978-1-56080-094-1
Store SEG Online Store

There is one additional step in conventional processing of land and shallow-water seismic data before stacking — residual statics corrections. From the NMO-corrected gathers in Figure 1.5-26a, note that the events in CMP 216 are not as flat as they are in the other gathers. The moveout in CMP gathers does not always conform to a perfect hyperbolic trajectory. This often is because of near-surface velocity irregularities that cause a static or dynamic distortion problem. Lateral velocity variations caused by a complex overburden can cause move-outs that could be negative — a reflection event arrives on long-offset traces before it arrives on short-offset traces. Close examination of the velocity spectra indicates that some are easier to pick (Figure 1.5-27a) than others (Figure 1.5-28a). The velocity spectrum that corresponds to CMP 297 has sharp coherency peaks that are associated with a distinctive velocity trend. However, the velocity spectrum that corresponds to CMP 188 does not yield a distinctive trend, thus making it relatively difficult to pick (Figure 1.5-28a).

To improve stacking quality, residual statics corrections are performed on the moveout-corrected CMP gathers. This is done in a surface-consistent manner; that is, time shifts are dependent only on shot and receiver locations, not on the ray paths from shots to receivers. The estimated residual corrections are applied to the original CMP gathers with no NMO correction. Velocity analyses then are often repeated to improve the velocity picks (Figures 1.5-27b and 1.5-28b). With the improved velocity field, the CMP gathers are NMO-corrected (Figure 1.5-26b). Finally, the gathers are stacked as shown in Figure 1.5-29b. For comparison, the stack without the residual statics corrections is shown in Figure 1.5-29a. Reflection continuity over the problem zone between midpoints 53245 has been improved.

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