余弦振幅加权定向地震波束形成方法

发布时间：2019-05-15 02:10

【摘要】：可控震源进行地震勘探时，由于单震源激发能量较弱，可采用相控震源系统来提高激发信号能量。但相控震源系统存在搬运困难、震源间的非一致性等问题，可以利用接收端地震波束形成方法来提高单震源数据质量。接收端地震波束形成方法是对地震数据进行预处理的方法，对震源间的一致性和控制精度没有严格的要求，因此相对相控震源系统应用起来比较灵活、高效。对于常规的接收端地震波束形成方法，如果地震勘探测区的噪声很强，就需要增加叠加炮数N来提高合成后的地震数据中有效地震波的能量，，从而达到提高数据质量的目的。由波束形成理论容易得出，波束的宽度将随着叠加炮数N的增大而减小，若增大N后，使得有效地震波束宽度无法覆盖全部检波器排列，那么，常规的接收端地震波束形成方法合成的地震数据将难以满足后续数据处理过程要求。针对上述问题，本文提出一种基于接收阵列的余弦振幅加权定向地震波束形成方法（Seismic directional beam-forming with the Cosine amplitude distribution，SDBCAD）。SDBCAD方法首先对各单炮记录乘以相应的余弦振幅因子值，然后进行时间域的延时叠加生成定向地震记录。使得合成后的有效波束范围展宽，同相轴连续范围延长，进一步改善合成单炮记录的质量，提高目的层横向分辨率，为后续数据处理提供了更高质量的数据。首先，阐述了定向地震波束形成理论。推导了阵列地震波束的方向因子，根据方向因子得出了波束的主要特性，分析并研究了影响地震波束特性的主要参数。其次，阐述了余弦加权定向地震波束形成原理与方法。推导了余弦加权波束的方向因子，分析了影响余弦加权地震波束特性的主要参数：震源（单炮记录）数量、炮点间距、加权系数矩阵等，并研究了各参数对地震波束的影响。给出了余弦加权波束形成的参数选取方法和定向地震记录合成方法。再次，对余弦振幅加权方法进行了初步的数值模拟。建立了一个水平层状地质模型，利用射线追踪的方法合成了多个单震源地震记录，并给出了单震源、均匀加权方法、余弦加权方法合成的单炮记录。通过对比三种方式的单炮记录，说明了均匀加权方法能够实现地震波束定向，提高地震数据质量；余弦加权方法增大了有效的地震波束范围，使目标地层同向轴更加连续，提高了地震记录的整体质量。最后，在研究了方法理论结果与数值模拟结果差异的基础上，对余弦加权波束形成方法参数进行了优化设计，并利用野外实验数据对比证明了方法的有效性。
[Abstract]:When vibroseis is used for seismic exploration, because the excitation energy of single source is weak, the phased vibroseis system can be used to improve the excitation signal energy. However, the phase vibroseis system has some problems, such as difficult transportation and inconsistency between sources. The seismic beamforming method at the receiving end can be used to improve the quality of single source data. The seismic beamforming method at the receiving end is a preprocessing method for seismic data, which has no strict requirements for the consistency and control accuracy between sources, so it is more flexible and efficient than the phased vibroseis system. For the conventional seismic beamforming method, if the noise in the seismic exploration survey area is very strong, it is necessary to increase the superposition number N to improve the energy of the effective seismic wave in the synthesized seismic data, so as to achieve the purpose of improving the data quality. It is easy to obtain from the beamforming theory that the width of the beam will decrease with the increase of the number of superimposed beams N. If the effective seismic beam width can not cover all geophone arrangement with the increase of N, The seismic data synthesized by conventional seismic beamforming methods at the receiving end will be difficult to meet the requirements of subsequent data processing. In order to solve the above problems, a cosine amplitude weighted directional seismic beamforming method based on receiving array (Seismic directional beam-forming with the Cosine amplitude distribution,SDBCAD) is proposed in this paper. SDBCAD method first times the corresponding cosine amplitude factor value for each single shot record. Then the time domain delay superposition is carried out to generate directional seismic records. The effective beam range after synthesis is widened and the continuous range of in-phase axis is extended, which further improves the quality of synthetic single gun record, improves the transverse resolution of the target layer, and provides higher quality data for subsequent data processing. Firstly, the theory of directional seismic beamforming is expounded. The direction factor of array seismic beam is derived. according to the direction factor, the main characteristics of the beam are obtained, and the main parameters affecting the seismic beam characteristics are analyzed and studied. Secondly, the principle and method of cosine weighted directional seismic beamforming are described. The direction factor of cosine weighted beam is derived, and the main parameters affecting the characteristics of cosine weighted seismic beam are analyzed, such as the number of sources (single shot record), the distance between shot points, the weighting coefficient matrix, etc., and the influence of each parameter on seismic beam is studied. The parameter selection method and directional seismic record synthesis method of cosine weighted beamforming are given. Thirdly, the cosine amplitude weighting method is simulated. In this paper, a horizontal layered geological model is established, and several single source seismic records are synthesized by ray tracing method, and the single gun records synthesized by single source, uniform weighting method and cosine weighting method are given. By comparing the single gun records of the three methods, it is shown that the uniform weighting method can realize seismic beam orientation and improve the quality of seismic data. The cosine weighting method increases the effective seismic beam range, makes the coaxial axis of the target strata more continuous, and improves the overall quality of seismic records. Finally, on the basis of studying the difference between the theoretical results of the method and the numerical simulation results, the parameters of the cosine weighted beamforming method are optimized, and the effectiveness of the method is proved by comparing the field experimental data.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P631.4

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