Effects of Surface Roughness or Diffusivity on Migration, and Lateral and Vertical Resolution

When the wavelength of the roughness of a reflector surface is much Iess than the wavelength of the lateral wavelet it confounds the process of migration and produces a vertical effect that appears as a velocity gradient when the data are inverted. Lateral effects and vertical effects become indistinguishable and the problem is irreparable by any processing of the data. The problem is: more acute on high-resolution data than lower-resolution data because surface roughness is a small-scale feature. For it to affect the data, wavelengths must be dimensionally similar to the scale of the roughness. The real data example shown, for instance, had a peak frequency of about 500 Hz and a dominant frequency of about 350 Hz. That is not to say that the effect might not be seen ·on low-frequency data, just that opportunities increase with higher frequencies. An interpreter aware of the effect of surface roughness might know to consider both possible interpretations, but it requires independent information, such as a onedimensional vertical velocity log or other geological knowledge to separate the two. The distinction between the two is geologically significant. Surface roughness and velocity gradients have different geological implications, so distinguishing the two affects the geological interpretation of the region in question.