Excitation Mechanism And Wavelet Processing Of The Air Gun Source

The air gun source is a good reproducibility, green, reliable source. For marine seismicdata processing and interpretation, the far field wavelet is an important parameter. With theincreasingly widespread application of air gun array, how to real-time access the far fieldwavelet of the array becomes a subject, which exploration workers and researchers areconcerned about. But in production, it could not meet the requirements of recording the farfield wavelet. Calculating the far field signature of an air gun array from the near fieldmeasurements is feasible.And in order to get a high-quality source wavelet air-gun arraymultiple tests are needed to select the best of the array parameters. It must invest a lot ofmanpower and resources. So using the wavelet theoretical simulated to solve the problemsencountered in the measurement is necessary.The conventional air-gun array is made of all guns at the same depth. It is easy to operate,but the ghost effect is obvious. Using the over/under source, we can attenuate the ghostsgenerated at the source side. Based on the over/under source, this paper proposes themulti-level source which consists in placing sub-arrays at different depths and firing them in asequence. This makes the notch frequencies of the sub-arrays different. After superposition, itcan attenuates the source ghost. The sub-arrays in different depths are regarded as the over/under sources. Then we separate the up-going and down-going events. In marine seismicexploration, for the simulation of the far-filed wavelet excited by the air-gun array, thecommonly used time-domain algorithm involves resampling, and thus there is a calculationerror. According to the relationship between the phase of the frequency domain and the timedelay in time domain, this paper proposes to transform the measured near-field wavelet to thefrequency domain using the Fourier transform, then do the decomposition and synthesis of thespectrum in the frequency domain.After that, we transform it back into the time domain.Using this algorithm, we can obtain the precise single gun source wavelet and reliablefar-field wavelet. This approach also considers the impact of the virtual reflection.It canremove the ghost reflection while doing the wavelet decomposition.The data test proved that multi-level source can indeed attenuate the ghost included in thefar-field wavelet, which extends the effective bandwidth and benefits low and high frequencies. From the theoretical model and the actual data, we proved that the waveletdecomposition in the frequency domain not only improves the precision but also achieve theremoval of ghost reflection of the measured near field wavelet at the same time. The actualdata test results showed that the far-field wavelet can evaluate the stability of the array. Andusing the zero phase operator obtained from the far field wavelet, we can shaping waveletdeconvolution of the seismic data.It can improve the resolution of the seismic records.