1887

Abstract

Where subsurface structure is complex, reflection data from land seismic surveys often suffer triply - from statics variations, the presence of various types of noise, and imperfect moveout correction due to crossing events and rapidly varying non-hyperbolic moveout. For such data, velocity analysis, already difficult due to the non-hyperbolic moveout and crossing events, is further complicated by anomalies due to variations in the near-surface. Conversely, accurate statics estimation requires accuracy in the velocity model. Because the velocity and statics problems are intertwined for data from structurally complex areas, it is appropriate to treat the two problems as one. Modem practice for data from structurally complex areas is to base velocity analysis on iterative use of prestack depth migration in conjunction with some process such as depthfocussing analysis. We propose to incorporate into this iterative velocity analysis a statics-estimation procedure that also utilizes prestack migration. When applied to staticscontaminated data, the prestack depth migration will correct the data for non-hyperbolic moveout, dipping, and crossing events, provided that the velocity model is sufficiently accurate. These prestack-migrated data are then stacked, and the stacked traces are input to a multi-offset modeling that generates an unmigrated reference trace for each of the traces in the unstacked data. Cross-correlation of each data trace with its associated reference trace gives a time shift for that data trace. The derived shifts are then used in a conventional statics-estimation procedure under the familiar assumption of surface-consistency. Tests with statics-contaminated Marmousi model data show that even where the initial velocity model is poorly known, the migration-based method produces acceptable i~itial- stage statics estimates. After applying the method Iteratively in conjunction with a migration velocity analysis, alternating between statics and velocity estimation, both velocity and statics solutions are improved, producing a good statics solution in the Marmousi data after just two iterations. Further iterations can then be directed solely towards improvement of the velocity model.

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/content/papers/10.3997/2214-4609-pdb.313.112
1995-08-20
2024-03-29
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http://instance.metastore.ingenta.com/content/papers/10.3997/2214-4609-pdb.313.112
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