Patent ID: 6311133
Filing Date: 2001-10-30
Classification: G01V

Abstract:
A method of performing prestack migration of seismic events for imaging a part of an underground zone from a series of a number N.sub.s of seismic reflection cycles, comprising successive emission of elementary wavefields, each elementary wavefield defined by association of a seismic signal W(t) and of a point of emission defined in a series of points of emission S.sub.i with 1.ltoreq.i.ltoreq.N.sub.s, seismic receivers located in positions R.sup.j.sub.i receiving seismic signals reflected by the underground zone in response to each of the wavefields, with signals received by each seismic receiver being recorded as time-dependent seismic traces d.sup.j.sub.i (t), wherein for a given velocity model, the method comprises the following steps:a) defining a slowness vector p having components p.sub.1 and p.sub.2 assuming a series of previously defined values;b) defining, for a given slowness vector p and for a given point of emission S.sub.i, a time lag function t.sub.0 (p, i);c) applying the time lag function t.sub.0 (p, i) to each elementary wavefield associated with point of emission S.sub.i and forming a surface composite wavefield by spatiotemporal superposition of elementary wavefields to which such a time lag is applied;d) applying the time lag function t.sub.0 (p, i) to seismic traces d.sup.j.sub.i (t) marked by a pair (i,j) and forming a surface composite trace field by spatiotemporal superposition of the seismic traces to which the time lag is applied,e) performing migration of the surface composite trace field using the surface composite wavefield, by modelling propagation of the surface composite wavefield and retropropagation of the surface composite trace field, and combining the modelled propagation of the surface composite wavefield and the retropropagation of the surface composite trace field at any point of the zone to be imaged,f) repeating steps c) to e) for all values assumed by the components p.sub.1 and p.sub.2 of the vector p, andg) for any set value of the second component p.sub.2 of the vector p, stacking the results of combinations of the surface composite wavefield and the retropropagation of the surface composite tracer field to obtain a migrated image associated with the set value of p.sub.2, to thereby perform prestack migration.