海上立体气枪阵列信号模拟与设计方法研究

发布时间：2018-05-02 05:48

本文选题：子波模型 + 立体枪阵　；参考：《中国海洋大学》2015年博士论文

【摘要】：海上气枪阵列被广泛用于海上地震勘探。因其具有能量大、稳定性好、应用范围广等特点而成为地球物理学家研究的热点。随着海上高分辨率地震勘探的发展,海上宽频震源已成为高分辨率地下成像的基础。立体气枪阵列可以很好地解决有震源虚反射引起的陷波效应,拓宽震源信号的有效频带,获得理想的宽频地震波信号。气枪震源的远场子波是不仅是衡量震源性能的重要指标,还是地震资料处理中的重要输入数据。实际中可通过现场实际测量来获取确定性的远场子波记录,但对于气枪震源来说,其设计具有很大的灵活性与多样性,需要反复试验来获得最佳枪阵设计。如果仅通过现场实测的方法来进行验证,则会耗费大量时间和费用。气枪子波模型则可以方便地对枪阵的远场子波进行模拟,极大地提高了枪阵设计的效率,并且可以对枪阵信号进行全面的研究,包括其气泡半径、气泡壁速度、枪阵信号的方向性等。而气枪本身的子波一致性和稳定性保证了这种方法的可靠性。气枪子波模型方法的实现主要依赖于模型本身的合理性和准确度,因此,进行气枪信号模拟研究,建立精确的气枪子波模型具有很高的研究价值和实际意义。本文首先对气枪的运作原理及其信号产生及影响因素过程进行了详细描述,总结了前人建立的气枪子波理想模型,以及对理想模型的各种修正。在现有的范氏气体气枪子波模型的基础上,考虑震源虚反射对单枪气泡振荡过程的影响。震源虚反射是海面对气枪上行压力波的反射,因此也会连同静水压力对气泡产生压力影响,从而对信号子波有改造作用。由于不同类型的气枪在构造上的差异而造成了在相同激发参数和条件下产生的信号子波有所差异,因此需要对依赖于实际气枪类型的参数根据实测子波进行标定。而对子波进行实际测量时,记录系统本身存在的频率响应和采样周期会对采集到的信号子波产生一定的影响,因此在进行标定过程中需要将模拟所得的子波进行滤波和重采样之后再与实际资料进行比对,以保证标定结果的准确性。最终模拟的子波与实测结果非常相近。在建立的气枪单枪子波模型基础上发展了气枪阵列子波模型,考虑了枪阵内气枪间的相互干扰作用等因素,最终的模拟结果与实测资料比较接近。研究立体延时气枪阵列激发理论,建立了延时激发的气枪阵列子波模型。对立体枪阵设计方法及其效果进行了研究,探讨了立体枪阵的深度组合、深度间隔以及气枪层数等对虚反射压制效果的影响。根据已有的立体震源设计方法,结合信号子波模拟模型,针对实际海上勘探要求和实际条件,设计并对比了两层和四层气枪震源,最终试验效果证明了所设计的立体枪阵的优势,取得了良好的应用效果。
[Abstract]:Offshore air gun arrays are widely used in offshore seismic exploration. Because of its large energy, good stability and wide range of application, it has become a hot spot of geophysicists. With the development of offshore high-resolution seismic exploration, offshore broadband seismic source has become the basis of high-resolution underground imaging. The stereoscopic air-gun array can solve the notch effect caused by virtual reflection of the source, widen the effective frequency band of the source signal, and obtain the ideal wide-band seismic wave signal. The far-field wavelet of air-gun source is not only an important index to measure the source performance, but also an important input data in seismic data processing. In practice, deterministic far field wavelet records can be obtained by field measurements, but for air gun source, its design is flexible and diverse, so it is necessary to repeatedly test to obtain the best gun array design. If it is verified only by the method of field measurement, it will cost a lot of time and cost. The air gun wavelet model can simulate the far field wavelet of the gun array conveniently, greatly improve the efficiency of the gun array design, and can conduct a comprehensive study of the gun array signal, including its bubble radius, bubble wall velocity. Directionality of gun array signals, etc. The wavelet consistency and stability of the air gun itself ensure the reliability of this method. The realization of the air gun wavelet model mainly depends on the rationality and accuracy of the model itself. Therefore, it is of great research value and practical significance to study the air gun signal simulation and establish an accurate air gun wavelet model. In this paper, the operating principle of the air gun and its signal generation and influencing factors are described in detail, and the wavelet ideal model of the air gun established by the predecessors is summarized, as well as the modification of the ideal model. Based on the existing van's gas gun wavelet model, the effect of hypotopic reflection on the oscillating process of single gun bubble is considered. The virtual reflection of the seismic source is the reflection of the upward pressure wave of the air gun on the sea surface, so it will also influence the bubble pressure together with the hydrostatic pressure, thus the signal wavelet can be modified. Due to the difference in structure of different types of air gun, the signal wavelet produced under the same excitation parameters and conditions is different, so it is necessary to calibrate the parameters depending on the actual type of air gun according to the measured wavelet. In the actual measurement of wavelet, the frequency response and sampling period of the recording system will have a certain impact on the signal wavelet. Therefore, in order to ensure the accuracy of calibration results, it is necessary to filter and resample the simulated wavelet and compare it with the actual data in the process of calibration. The simulated wavelet is very close to the measured results. The air gun array wavelet model is developed on the basis of the single gun wavelet model, and the interaction between the air guns in the air gun array is considered. The simulation results are close to the measured data. In this paper, the theory of stereoscopic delay air gun array excitation is studied, and the wavelet model of air gun array excited by delay excitation is established. The design method and effect of stereo gun array are studied, and the effects of depth combination, depth interval and number of air gun layers on the effect of virtual reflex suppression are discussed. According to the existing methods of stereo seismic source design, combined with the signal wavelet simulation model, according to the actual requirements and actual conditions of offshore exploration, the two-layer and four-layer air-gun seismic source is designed and compared. Finally, the experimental results show the advantages of the designed stereo gun array, and good application results are obtained.
【学位授予单位】：中国海洋大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：P631.46

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