Patent ID: 6094621
Filing Date: 2000-07-25
Classification: G01V

Abstract:
A method of determining prestack migration comprising the steps of:recording seismic reflection traces using source/receiver pairs which are arranged on top of a subsurface region to be explored and for each of which the source is separated from the receiver by a distance referred to as an offset,producing on a basis of the recorded traces, at least one collection of traces pertaining to a specific zone of the subsurface region, the traces having been sorted according to a given criterion,using a propagation velocity model pertaining to the specific zone in an (x,z) domain,calculating, in a first phase, only the transit times corresponding to the traces,migrating, before stacking and without weight correction, the sorted traces by using the propagation velocity model,using a dip map, established beforehand for the specific zone and in a same (x,z) domain as a velocity domain,determining, for each point M of interest selected in the (x,z) domain, at least one dip taken from the dip map,determining specular rays associated with the point M for the at least one dip and for a range of offsets defined beforehand,calculating a time characteristic and an amplitude characteristic of each of the specular rays, anddetermining a reflectivity at each point M of interest on a basis of the time and amplitude characteristics.