Abstract

Even though statics processing is well advanced and is routinely applied, interpreters are still required to evaluate seismic data that has either no statics corrections or poor statics corrections. It is a critical interpretation skill to recognize uncorrected statics and to correct for their effects. Poor decisions and dry holes are often the result of failure to do this. Since multifold seismic data has become the norm, statics are no longer time invariant. The method of flattening stacked data on a shallow reflector that worked so well for single fold data will show anomalous structure and isochron variation caused by the time-variant effects of uncorrected statics.Uncorrected statics can be identified by anomalous undulations in a shallow reflector, by the time-variant effects with increasing reflection time, and by the variations in optimal stacking velocities, all of which have been documented in the literature. Knowledge of these properties from stacked data observations can lead to robust estimates of the surface position delay profile necessary for all statics corrections. Although prestack analysis and correction provide the best solutions, full spatial and temporal corrections can be calculated easily and applied to the interpretation of stacked data on most work stations to enable quicker, less expensive decision making. Prestack reprocessing is only one action that may result from a quality poststack analysis. Stacked data time picks can be fully corrected with a statics term and a velocity term. Partial corrections, applied only to the center trace of a static-causing body can be made without knowledge of the exact surface position delay model. The ratio of central trace delays of two reflectors is approximately equal to the ratio of effective spread lengths used to stack the two reflectors. This method is applied to a real data example published last year in Geophysics where the anomalous isochron thinning is accurately predicted.

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