Lab 6: Static Corrections

Seismic reflection data in different traces are not always lying on a hyperbole for a horizontal reflector. Reflected data have certain displacement due to the different length of ray paths. Static displacements can be caused by topographic conditions (difference in elevation), weathered/unconsolidated layer; slow velocity, different borehole/gun and cable depth, tidal wave as well as water layer effect. 
Figure 1: Topographic and weathered layer effect of seismic survey
Thus, static corrections are applied to seismic data in order to compensate for various effects on the data such as those related to near surface, variations in elevations, weathering, and reference to a datum. By applying static corrections, we aim to determine the reflection time assuming the existence of a flat surface plane with no weathering layer. 
These corrections include:

 1. Elevation static correction, which accounts for variable elevations of the sources and receivers.

2. Residual static correction, which accounts for lateral variations in the velocity and thickness of the weathering layer (WL).


Surface-Consistent Residual Static Correction in Practice 

 The following parameters are important when picking the time shifts in practice:

 (a) Maximum allowable shift: which is the maximum shift allowed for cross-correlations where a value between 30 and 40ms is reasonable.

(b) Correlation window: where it should be chosen in an interval with the highest possible SNR ratio.
Figure 2: CMP gather shot 250


Figure 3: Before Static Correction


Figure 4: After Static Correction

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