Numerical Simulation Of Air-gun Array And Its Application

Marine source is important to high-resolution marine seismic exploration. As the most widely used marine source, air-gun has many advantages with stable behavior, well uniform wavelet, broad spectrum, adequate low and high frequency. For the processing and interpretation of marine seismic data, air-gun far-field wavelet is an important parameter. It is one of the parameters necessary for prestack and source model. In practice, the measurement of air-gun array need much time, manpower, material resource, and consume much. During the process of air-gun array design, we have to measurement the array wavelet for different conditions again and again, and determine the optimum parameters for air-gun number, operation pressure, depth, distance between guns, and the location of each gun in the array. Theoretic modeling of air-gun array source will solve these questions easily, and is superior to wavelet measurement. Now theoretic modeling of air-gun array source have been widely adopted in practice.Based on theoretical model provided by Johnson D. T. in 1994, we analyze the reasons for difference between modeling wavelet and measurement wavelet, and point out that the discrepancies between air-gun theoretic model and practical process is one of the main issues. The high pressure gas will be throttled by Exhaust valve, and its motion is throttling expansion, not satisfied with free bubble theory. The pressure in bubble is very low at the moment of forming of source wavelet. When the exhaust valve is closed, the gas with the bubble oscillation reduces, causing the bubble impulse lower the pressure impulse obviously. With the analysis above, we modify the numerical method, and choose the optimum initial parameters, the modeling wavelet matching the measurement well.After analyzing the pressure field character of air-guns includinginteractions, the theoretic model of air-gun is modified with varying hydrostatic pressure, the modeling wavelet of two interaction guns is consistent with the measurement.We apply the numerical algorithm above to I/O 750 in3 air-gun subarray, and compare the modeling array wavelet with measurement, proved the validity of numerical simulation.Finally, we mention the design of air-gun array for high-resolution seismic exploration of Shengli Oil Field, and its application in seismic acquisition in practice, and include that numerical simulation of air-gun array is an important method to design high-resolution array source, aimed at the difficulty met in practice. With air-gun array numerical simulation, we can design effective marine source, and solve the problem on difficult acquisition and bad seismic data in beach and offshore.