Air Gun Source SignatureAnalysis And Study In Bohai Sea

Air-guns are the widely applied artificial source in offshore seismic prospectingcurrently. There are many feathers in air-gun such as producing similar wavelets, stableperformance, wide frequency range, rich high and low frequency components and soon. We can get excellent wavelet more easily by using air-gun source, this ensures highquality of the seismic profiles after data processing and meet the requirements ofexploration work.Currently, research on air-gun sources has already shifted from a single gun to theair-gun array. The features of wavelet generated by air-gun array get more advantagesthan that generated by a single gun, its energy is stronger and weaken the bubble effect.There are ever-changing combinations of air-gun array, it is essential to choose propercombination of air-gun array for different exploration depth.In this paper, we start from the bubble oscillation theories, feathers and impactfactors of air-gun wavelets, base on the actual acquisition of near-field wavelets andaccording Ziolkwski theory, we deduce the far-field wavelets of air-gun array. We alsocombinate the raw data received by24high-precision digital seismic towrope properly,analyse and compare the waveform, energy and frequency spectrum of waveletsgenerated by single gun and cluster gun, especially those which generated by planarand multiple-level sub-array, planar and multiple-level air-gun array. Since the place ofdata acquisition is shallow water area, the sinking depth of air-gun array is limited, andinfluencing factors of source boat itself to the air-gun can not be ignored and otherreasons make big differences between the actual wavelets and theory wavelets, thenegative pulse energy of some wavelets is higher than the main pulse. Meanwhile, theenergy and frequency of raw data received by24high-precision digital seismictowrope also shows significantly advantages that cluster gun is better than single gun and multiple-level air-gun array is better than planar array.This paper focuses on the wavelets analysis and comparison generated byfront-after, left-right sinking mode of multiple-level array, due to the different sinkingdepth is the key influencing factors to the air-gun wavelets, we do a lot of experimentsof different sinking depth about this two multiple-level arrays. we can found that whenthe sinking place of large volume sub-array shallow than small volume sub-array, thewaveform and frequency spectrum of wavelets are often better. Meanwhile calculateconvolution operator, establishing the relationships between far-field wavelets deducedby near-field wavelets and the wavelets extracted from towrope.Combined with the raw data received by towrope, after wavelet contrast to asingle gun, cluster gun and array, we select the plane array and left-right sinking modeto acquise data from the same survey lines. We get stack profile after data processing,and it shows the effect of multiple-level array is more desirable.