Simulation of Spark Source Wavelet Under Multibubble Motion

Marine spark sources are widely used in high-resolution marine seismic surveys.The characteristic of a wavelet is a critical part in seismic exploration;thus,the formation and numerical simulation of spark source wavelets should be explored.In studies on spark source excitation,the acoustic field generated by the interaction between bubbles constitutes the near-field wavelet of a source.Therefore,this interaction should be revealed by studying complex multibubble motion laws.In this study,actual discharge conditions were combined to derive the multibubble equation of motion.Energy conservation,ideal gas equation,and environmental factors in the discharge of spark source wavelets were studied,and the simulation method of an ocean spark source wavelet was established.The accuracy of the simulation calculation method was verified through a comparison of indoor-measured signals using three electrodes and the spark source wavelet obtained in the field.Results revealed that the accuracy of the model is related to the number of electrodes.The fewer the number of electrodes used,the lower will be the model's accuracy.This finding is attributed to the statistical hypothesis factor introduced to eliminate the coupling term of the interaction of the multibubble motion equation.This study presents a method for analyzing the wavelet characteristics of an indoor-simulated spark source wavelet.

Simplifi ed traditional bubble-motion equation and air-gun wavelet simulation based on a Van der Waals gas model

An air-gun source is the most commonly used excitation method in off shore seismic exploration.The excitation characteristics of an air-gun source aff ect seismic data quality.Far-field wavelet simulation is an important approach to study these characteristics.Compared to the measured wavelet,far-field wavelet simulation based on a traditional bubble-motion equation and ideal gas wavelet model has some disadvantages,such as a greater amplitude and smaller pulse attenuation velocity.Here,we start from the linear acoustic wave equation in the spherical coordinate system to deduce an improved,simpler bubble-motion equation and develop a Van der Waals gas wavelet model based on this equation.Unlike the existing methods,our method considers the high-pressure environment during actual excitation,heat exchange between the bubble and outside water,and change in the air fl ow at the muzzle.The results show that the far-fi eld wavelet simulated using this model is closer to the measured wavelet than that of the ideal gas wavelet model.At the same time,our method has a more succinct equation and a higher calculation effi ciency.

Experiment and Simulation of Large Capacity Air-guns in Deep Structure Exploration

The air-gun source has important applications as a new, environmentally, green active source in regional scale deep exploration. In the past, the air gun source was used mainly in smallscale, high-resolution shallow oil exploration, but has a lack of adequate research in deep exploration. In order to study the selection of work parameters and field conditions of the air gun source in deep exploration, this paper does the following work： （1） analyze the characteristics of the air gun source using air gun experiments; （2） simulate the air gun signal and air gun-array signal based on the theory of free bubble oscillation to analyze the influence of bubble oscillation and study the wavelet energy and spectrum characteristics needed in deep exploration; （3） on the basis of theoretical simulation, study the influence of work parameters, such as air-gun capacity, work stress and depth on air gun signal and analyze the influence of air-gun array inspired moment and spacing of different air guns on air gun-array signals; and （4） study energy reflection and transmission coefficients for different underwater interfaces, which is very useful for choosing suitable field conditions.