GB1342438A - Seismic exploration - Google Patents

Abstract

1342438 Wave-energy exploration of a medium SOC NATIONALE DES PETROLES D'AQUITAINE 28 Jan 1972 [2 Feb 1971] 4215/72 Heading H4D In a system for exploring a medium by emitting waves into it from at least two sources at different instants and receiving waves reflected from within the medium, the time interval separating two consecutive wave emissions respectively produced by different ones of the sources is less than the longest go-and-return wave travel time T of interest, the time interval separating two consecutive emissions from any one source is at least equal to the longest go- and-return time T, and the emission instants are such that cross-correlation, over time T, of the sequence of emission instants of at least one source with the combined sequence of emission instants of all the sources gives a correlation function in which the ratio of the amplitude of the maximum peak to the amplitude of each secondary peak is greater than the ratio of the amplitudes of received signal samples separated by time intervals corresponding to the time intervals separating the maximum peak from the secondary peaks. These conditions enable the use of several sources concurrently for economy of exploration time, without the need to synchronize the sources. In the embodiment described, for land or marine seismic exploration, two or three pulsesources and one or two lines of seismometers are used in a roll-along survey method. The source emission sequences and received signals are separately recorded. To identify the received signal components associated with any one emission source, the recorded emission sequence of that source is cross-correlated with the received signal record; the same is done for each of the other sources.