Phase mysteries

20 years ago, when companies made their 3D-merges they weren't very particular about adjusting phase and time. But as you get closer to "drill or drop" these things matter. The picture shows cross-correlation between a 2D and a 3D survey.

Cross correlation

To assure uniform phase and time in my 3D-merges I do a cross correlation between a regional 2D survey and my current 3D. The 2D survey I know is uniform in phase and time. In this picture I was working with a small 3D-merge done 20 years ago.

No need to go into technicalities, but focus on the black white line running through the center of the picture. if the 2D and the 3D had the same phase and time, this line would be white-black-white, centered on 1500ms. For the central part of this picture this seems to be the case. The left part, however is white over black centered on 1490ms. So the 3D on the left is 90 degrees rotated and 10ms too shallow, compared to the central part.

The vertical fuzz are from two salt domes covered by my cross correlation. 2D-s and 3D will never correlate over salt domes.