Simulation Study On Signature Stimulated By Air-guns In Conditions Of Van Der Waals Gas

Air-guns are the important artificial seismic source in offshore seismic prospecting. It is the most important factor that wavelet characteristics of air-guns affect the effect of seismic exploration. And the signature is also a very important parameter in seismic data processing and interpretation, which has to be inputted on pre-stack processing and seismic forward and inverse model. High frequency signature stimulated by air-guns prospects fine structure of shallow oceanic crust. Low frequency signature stimulated by air-guns explores deep oceanic crust and upper mantle from far distance.In practice, signature stimulated by air-guns or air-gun arrays may be obtained in actual measurement, but the measurements need much manpower, material resources and consume besides good external environment conditions. Not only signature simulated by the air-gun wavelet model can be close to measured signature, but also the air-gun wavelet model expends a little quantity of cost. The wavelet model has solved these questions easily and is superior to wavelet measurement. Researches and examples show that the performance of air-gun source is steady and the wavelet has good compatibility, which is unable to change with the lifetime rise. The wavelet model has these characteristics of validity and authenticity. Therefore, it has important value of the theory and application to study signature simulation.According to the principles, behaviors and influential factors of air-guns, various wavelet models of the single air-gun are concluded. Then the new single air-gun wavelet model of Ideal Gas is established from the difference between the modeling wavelet and the measured wavelet. The open quasi-static thermodynamic system in conditions of Ideal Gas is drawn in the new wavelet model. The modeling wavelet is close to the measured wavelet when the air-gun operation pressure is small. But with increase of the operation pressure the modeling wavelet greatly deviates from the measured wavelet. In view of the problem, the author judges that gas in the air-gun does not correspond to the conditions of Ideal Gas with increase of the operation pressure. So there is very big error caused by Ideal Gas Equation of State.The single air-gun wavelet model of Van der Waals Gas is established. When gas in the air-guns is regarded as Van der Waals Gas and Van der Waals Equation is drawn, the single air-gun wavelet model of Van der Waals Gas based on the open quasi-static thermodynamic system and the bubble oscillation theory is established. At the same time, the wavelets stimulated by different types of air-guns are non-uniform. The single air-gun wavelet model of Van der Waals Gas can determine various types of air-gun parameters to simulate signature of the same air-guns of different volume. Test results show that the signature simulated by the model remains close to the measured wavelet when the air-gun operation pressure increases.The GI gun wavelet model of Van der Waals Gas and the air-gun array wavelet model of Van der Waals Gas are developed. The single air-gun wavelet model of Van der Waals Gas has these characteristics of validity and authenticity, so the two wavelet models are established. The former controls the signature by setting the gas ejection. The latter is established by interaction between air-guns in the air-gun array. Acceptance tests demonstrate that the two models can be close to measured wavelet.Based on the theories and algorithms, the air-gun wavelet simulation software of Van der Waals Gas is programmed. Aimed at the difficulty and target in practice, it can efficiently, correctly, sparingly achieve the design of the air-gun arrays and the marine seismic source of predominant performance is obtained. It is good effects that the air-gun array parameters obtained by the design of the air-gun wavelet simulation software of Van der Waals Gas are applied into offshore seismic prospecting.