Image rays and the old myth about correcting time migrated positioning

One of the problems of using seismic data to image the subsurface is that, if there is significant lateral variation in the overburden, standard time migration may image a reflector in the wrong location. This is obviously a problem if you have it in mind to drill a well into it. These days, it would be routine to apply a depth migration algorithm that can image the reflector in the right location, so long as the velocity field is correct. However, back in the 1980s it was common to try to estimate the size of the time-migration mislocation using image ray construction, and this method is still sometimes used today. First Break asked Rodney Calvert of Shell International to explain why this is not a good idea.