The Air-gun Subwave Simulation Experiment Based On Ideal Gas Model

The air-gun hypocenters,as a type of non-pollution equipment, is used for producing shock wavelet for ocean exploration. The signature of its wavelet characteristics not only affect the effect of seismic exploration, but also it is an important parameter in seismic data processing. In the practical application, the measurements of wavelet consume much, and it needs good external environment. The problem is solved conveniently and effectively by the air-gun wavelet models. It is very simple and quick to obtain the wavelet through the computer simulation. For the practical measurement it has incomparable advantages. Therefore it is of great significance to research the air-gun wavelet simulation. One of the key for designing air-gun source is how to control the characteristics of the wavelet,to meet the exploration requirements.Air-gun source has gradually become the main form of marine seismic excitation. The history and present situation about air gun research at home and abroad is summarized in this paper, and the working principle of air-gun is also discussed. Besides, the gun structure of Sleeve gun, Bolt gun and G gun is compared. And then the shock process of the bubble is described. Pulse energy, P/B ratio, bubble period and wavelet spectrum are the four main parameters of evaluating the air-gun source wavelet. The four parameters is presented in detail and a simple description of some factors that affect the source wavelet is given in this paper.Anton Ziolkowski model, Schulze-Gattermann model, Safar model and Johnson model are the main air-gun models at this stage. The characteristics and advantages and disadvantages of the four models are summarized in the paper. Then the calculation of the model equation based on the "free bubble oscillation " theory is simplified in the following part. The three main algorithms that developing the focal simulation software requires are analyzed. That is the Runge-Kutta processing function algorithm, the source wavelet analog drawing algorithm and the fast Fourier transform algorithm. Finally a lot of comparative analysis to study the impact of the parameters on the source wavelet analog graphics from the air-gun, external environment and other parameters is done in the paper. All of these lay a good theoretical basis for selecting parameters on actual measurement.