Patent ID: 7706211

Claim:
A method of determining a seismic velocity, comprising steps of: (a) providing two or more seismic receivers in the subsurface formation at predetermined distances from one another; (b) selecting a seismic receiver m from the two or more seismic receivers as the location of a virtual source; (c) selecting another seismic receiver k from the two or more seismic receivers; (d) activating a seismic source at a location n, thereby exciting a wave in the subsurface formation; (e) recording a wave signal trace u nm (t) against time t, at the seismic receiver m; (f) recording a wave signal trace u nk (t) against time t at the seismic receiver k; (g) cross correlating the wave signal traces u nm (t) and u nk (t) to obtain u conv nmnk (t); (h) repeating steps (d) to (g) inclusive, for different locations n; (i) summing u conv nmnk (t) over all locations n, to obtain a virtual signal trace u vs mk (t) which corresponds to the signal received by the seismic receiver k from the virtual source at the position of seismic receiver m; and (j) deriving the seismic velocity based on the time of first arrival of the wave in u vs mk (t) and the predetermined distance between the seismic receiver m and the seismic receiver k; further including, before step (g), at least one of removing part of the wave signal trace u nm (t) that contains a component of the wave field at seismic receiver m traveling in a direction other than from seismic receiver m to receiver k and removing part of the wave signal trace u nk (t) that contains a component of the wave field at the receiver k traveling in a direction other than from seismic receiver m to receiver k.