Patent ID: 6868039
Filing Date: 2005-03-15
Classification: G01V

Abstract:
1. A method for determining a velocity model of seismic waves picked up by seismic receivers coupled with an underground formation, in response to the emission of subsoil seismic waves by a seismic source, after reflection by geologic interfaces of the formation, from multi-offset records of the waves, for each seismic event located for the multi-offset records and for each layer delimited by the interfaces comprising: a) from the prestack seismic records, constructing an iso-offset collection from which kinematic information or travel times associated with the event are extracted; b) selecting a velocity distribution around a reference velocity in the layer, that is sampled with a predetermined interval; c) for each velocity sample, applying an inversion technique at a fixed velocity so as to determine, from the travel times extracted from the iso-offset collection, a geometry of the interface for the velocity sample in order to obtain a series of interface/velocity pairs for the event; d) calculating the kinematic information associated with each obtained interface/velocity pair, for source-receiver pairs corresponding to multi-offset collections existing in the multi-offset seismic records; e) for each interface/velocity pair and for each multi-offset collection selected, evaluating coherence between calculated multi-offset travel times and the seismic records, and selecting for each multi-offset collection a travel time curve showing maximum coherence with the seismic records; f) applying a prestack kinematic inversion method using the multi-offset travel times obtained for all the multi-offset collections selected, in order to determine a geometry and a velocity of the layer being considered; and g) iterating n times steps a) to f) by considering for each iteration a velocity model obtained during a previous iteration as a reference velocity model to define the reference velocity, and wherein n is an integer.