Geophysical prospecting method using pseudo-random pulse sequences

Abstract

A geophysical prospecting method comprises injecting signal energy in the form of at least two pseudo-random pulse sequences of the complementary sequence type into an underground formation. Next, the signal energy is detected after it has been attenuated by passing through the underground formations in the form of response signals. The response signals are correlated with reference signals comprising at least two pseudo-random binary sequences to yield correlations. The correlations are summed so that the resultant signal which corresponds to the subsurface response signal does not have secondary lobes. The method is applicable to seismic prospecting and more particularly to cross-well seismic surveying. It is also applicable to acoustic prospecting for logging measurements. In a preferred embodiment, the pseudo-random sequences comprise a pair of Golay sequences.