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Air Gun Source Signature Analysis and Processing Technology Study

Author: LiGaoLin
Tutor: LiuHuaiShan
School: Ocean University of China
Course: Earth Exploration and Information Technology
Keywords: Air gun source signature bubble ghost earth attenuation mechanism general linear inversion predictive deconvolution
CLC: P631.4
Type: Master's thesis
Year: 2011
Downloads: 65
Quote: 0
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Abstract


Air gun is a common source in marine prospecting, and widely used in the petroleum exploration , geological survey and environment evaluation. The wavelet generated by air gun has good stability in certain conditions, so the design of array corresponding to the exploration task and purpose can be realized. For example, in the exploration of fine structure formation of the seabed, the air gun selected should be able to generate high frequency signal to meet the requirements of the resolution of the seismic profiles, so the fine structure features can be interpreted. In the deep geophysical exploration, the energy should be strong enough, to ensure the propagation distance and penetration depth to meet the requirements.In this paper, the bubble oscillation theories have been summarized, and realize several ideal bubble models which have already been discussed. And add many actual factors that affect the bubble oscillations into the bubble models, established a new model of bubble oscillation. The model of bubble oscillations behavior is described by van der Waals equation formulation, it’s closer to the real gas compared to previous statements by the ideal gas. Besides, the gas viscosity, the amount of gas emitted, water temperature and other working parameters are also taken into account which make the simulation results more in line with the actual. In this paper, the wavelets of different type air guns are simulated, and the result is very good. Provide a more accurate single wavelet for the latter array design, laid a good foundation for the simulation of air gun array.Ghost and the bubble effect is the most common marine seismic survey of interferences. The feature of ghost in the seismic profile is it shows reverse phase with the main pulse, and perform the notch effect in the spectrum. The existence of ghost in the seismic record influences the signal to noise ratio and resolution. Bubble effect is produced because the bubble will not only oscillate once before it come out the water, this make the length of the wavelet become longer and show energy tail interference. The study shows that the bubble effect will be enlarged with the propagation increased. And found that ghost have decreased bubble effect from observation of real seismic data.This paper will analysis the bubble effect in frequency domain combine with the earth attenuation mechanism to explain why the bubble effect is enlarged, and give a reasonable explanation. The reason that the bubble effect enlarged is that bubble energy is concentrated in the low position. And the energy of main pulse distributes uniformly throughout the band. As earth attenuation mechanism describes high frequency energy will decay rapidly, but the low frequency will decay little, so the rate of main pulse energy to bubble energy will become small quickly, that makes the bubble effect enlarged which show as energy of wavelet tail amplified. This paper also study the theory of ghost and draw a conclusion that ghost can weaken the bubble because there exit a time delay between ghost and the main pulse.In order to eliminate the bubble effect, this paper gives a general linear inversion method. This method is based on the convolution model of seismic data, the seismic data and the wavelet is the input, form a linear equation by the seismic data and the wavelet, the debubbling record can be by solving the linear equation. This method is tested by both models and real seismic data, and achieved good application result, the bubble effect is eliminated largely.This paper studies the air gun wavelet systematical, summarizes wavelet simulation methods from basic theory. And make some improvements to the previous models, the simulation result of new model is very close to the actual. And also give reasonable explanation of some phenomena in actual data process. Proposed an effective method to eliminate the bubbles, Formed a method of marine wavelet analysis and process. Obtained ideal results in practice.

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CLC: > Astronomy,Earth Sciences > Geology > Geology, mineral prospecting and exploration > Geophysical exploration > Seismic exploration
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