Marine data examples

One of the practical applications of datuming in seismic data processing is layer replacement Berryhill (1986); Yilmaz and Lucas (1986). The layer replacement refers to replacing the overburden velocity with the velocity of the substratum, thereby eliminating raypath bendings at the interface between the overburden and the substratum. Time migration after layer replacement can be a practical alternative to depth migration. Therefore, one of the most important things in layer replacement might be preserving the correct spectral property of the original data. The ability to preserve the correct spectral property in layer replacement techniques can be verified by the unitary characteristic of the datuming operator used in the layer replacement.

I applied the datuming algorithm to marine data to illustrate the effectiveness of the datuming algorithm. The near-offset section of a marine data set is displayed in Figures 8. This is the Gulf of Mexico data obtained by Amoco. The complex structure along the sea bottom causes raypath bending that induces distortions and disruptions on reflections beneath a complex structure. The dashed line in Figures 8 represents a datum along the sea floor defined by the first break picks. The near offset is 30 meters so I treat the data as if it were zero-offset and input it to the datuming algorithm.

The datuming to the sea floor is performed using phase-shift extrapolation with water velocity, 1500. m/s, and the result is displayed in Figures 9. To compare with the original data, I used the same water velocity in the process of upward continuing the data back to sea level. Unlike the Kirchhoff datuming Berryhill (1979); Bevc (1992) which loose some high frequency component, we can see that the datuming used in this paper preserve the spectral property of the original data after layer replacement. The difference between the original data and the data after layer replacement is shown in Figure 11 and confirms the nice property of the datuming operator used.

 

real-data
Figure 8 Gulf of Mexico near-offset data with first break picks overlaid.

 

real-sea-bottom
Figure 9 Golf of Mexico near-offset data datumed to the ocean bottom.

 

real-sea-surface
Figure 10 Golf of Mexico near-offset data redatumed to the sea level.

 

real-diff
Figure 11 The Difference between Figure 8 and Figure 10. It is too weak to see in the paper printout gray scale. You may try xtpen by clicking the button to see the difference.