Modelling the signature of clustered airguns and analysis on the directivity of an airgun array

摘要

Based on the Giles-Johnston approximation and the analysis of the mutual interaction between two bubbles at different distances, a model is established to simulate the signature of clustered airguns in offshore seismic exploration, concerning the practical factors which have effects on bubble oscillation such as the gun ports throttling and the heat conduction across the bubble wall. By using this model, the signatures of clustered airguns at different distances are calculated with the volume of airguns equal and unequal; the energy distribution of the airgun array signature in three-dimensional (3D) space is also analysed. The result of simulation indicates (1) the pressure wave emitted from bubble oscillation and the ghost wave reflected from the sea surface change the wave field around other bubbles, which makes it the primary source of the mutual interaction between bubbles; (2) with the distance decreasing, the mutual interaction between bubbles becomes strong, the bubble period increases, the primary peak amplitude decreases, and the primary/bubble peak amplitude ratio increases at first and then decreases afterwards; (3) as the distance between bubbles reduced, the bubbles with unequal volumes oscillate with the same period, and the frequency locking phenomenon occurs accompanying the violent bubble oscillation; and (4) the energy of the pressure wave is strongest down below the midpoint of the airgun array, while relatively weak in other directions, this can be used for true amplitude recovery in seismic data processing.