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Enhanced Residual Statics by Gradually Building a Velocity Model: A Case Study

Alghamdi, Ahmed S.*1; Afif, Omar H.1
(1) Geophysical Data Processing Division, Saudi ARAMCO, Dhahran, Saudi Arabia.

In areas with complex near surface and topographic variations, field statics do not generally fix all delays within the seismic traces. The complexities in the study area include large variations between areas of hard rock to areas covered by sheeted sands and sand dunes. The modeling challenges include long wavelength corrections, base of sand definition under the sand dunes, and imaging of complex structures, such as horsts and grabens. The near surface modeling used in this area includes elevation correction along with a sand dune term. Near-surface and structural complexities cause rapid changes in the RMS velocity model both vertically and laterally. This change led us to gradually fine-tune the RMS velocity model to help the residual statics corrections to calculate the delay correctly.

The residual statics correction method applies static time shifts between traces within a CMP gather and pilot traces depending on source and receiver locations in a surface consistent manner. Moreover, it is especially effective in estimating short-wavelength statics. Generally, for the initial velocity analysis, the function intervals are regularly spaced. This usually produces a good and smooth RMS velocity model that helps in computing better statics results. If the lateral velocity variation in the area is large, coarsely sampled velocity functions will prevent the residual statics technique from working properly.

This paper presents a 2D seismic line in a topographically complex area in which a velocity model is gradually built from a sparse model. This approach helps in computing the residual statics solution correctly and finding the correct time shift that balances all traces in time arrival order. Starting with a sparse velocity model, to compute residual statics, and iteratively building the desired finer sampled velocity model will eliminate cycle skips and discontinuities in the target horizons. This processing work flow shows good results when compared to a more conventional processing flow.

 

AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain