GB1520031A - Method of generating acoustic energy for seismic sureveying - Google Patents

Abstract

1520031 Generating acoustic energy for seismic surveying MOBIL OIL CORP 8 Jan 1976 [28 Feb 1975] 00633/76 Heading G1G Acoustic energy is generated in a water layer over-lying a subsurface formation to be surveyed by suspending a plurality of acoustic energy generators in the water layer and firing them in a sequence so as to produce a resultant acoustic pressure wave having a time-domain characteristic representative of the inverse of the distortion effect upon the wave as it reverberates in the water layer. It is shown in the Specification that the resultant acoustic pressure wave can have either a twopoint time-domain characteristic or a three-point time-domain characteristic. In the first instance an acoustic impulse of amplitude S is generated at a time t and a second impulse of amplitude S x R is generated at a time t + Tw, where R is the reflection coefficient of the water bottom. This second impulse may be directed either towards the water bottom or towards the water surface. In the second instance, an acoustic impulse of amplitude S is generated at time t, a second impulse of amplitude S x 2R is generated at time t + Tw and a third impulse is of amplitude S x R<SP>2</SP> is generated at time t + 2Tw, the second impulse being directed either towards the water bottom or towards the water surface. As described with reference to Fig. 9 (not shown), the generators are towed by a marine vessel which also tows a streamer of hydrophones. The generators may be arranged either as shown in Fig. 10 or as shown in Fig. 11. In Fig. 10, the generators E1-E16 are towed horizontally behind a boat 60. In the two-point case, generators El- E8 are fired simultaneously at time t to provide a resultant impulse of amplitude S, and generators E9-E16 are fired simultaneously at time t + Tw to provide a resultant impulse of amplitude S x R. In the three-point case, generators El to E4 are fired simultaneously at time t to provide a resultant impulse of amplitude S, generators E5 to E12 are fired simultaneously at time t + Tw to provide a resultant impulse of amplitude S x 2R, and generators E13-E16 are fired simultaneously at time t + 2Tw to provide a resultant impulse of amplitude S x R<SP>2</SP>. In Fig. 11, the generators El- E16 are towed vertically behind the boat. In the two-point case, generators E1-E8 are fired sequentially to provide a resultant downwardly directed impulse of amplitude S at time t and generators E9-E16 are fired sequentially, either from top to bottom or vice-versa, to provide a resultant impulse of amplitude S x R at time t + Tw. In the three-point case, three groups of generators are fired in the desired sequence to provide the impulses of amplitude S, S x 2R and S x R<SP>2</SP> at times t, t + Tw, and t + 2Tw respectively.