摘要
多次波问题在地震勘探中普遍存在,在某些地区尤为突出。由于多次波问题的复杂性,目前仍未很好被解决。作为一种相干噪声,多次波降低了地震资料的信噪比,制约着分辨率的提高。如果不能有效地压制,多次波将影响地震成像的真实性和可靠性,以及干扰地震资料的解释。则如何有效地识别、压制多次波是地震资料特别是海洋地震资料处理中的关键和难点之一。因此,多次波压制方法及应用研究不仪具有重要的理论意义,而且有一定的实际意义和应用价值。
本论文首先针对当前多次波压制研究和应用的现状,分析了其存在的问题。接着详细地论述了多次波的成因、分类、运动学特征、波场特征,并介绍了多次波的识别技术。然后从方法的原理、应用条件、压制效果、优点与不足等方面系统地论述了几种主要的多次波压制方法,并借助Promax、Focus等商业软件,进行了相应的应用试验研究。针对目前多次波压制主要集中在单一方法的研究,本文发展了组合多重压制方法,分别从组合的物理基础、依据、原则进行了研究,在此基础上提出了两种组合方式,并给出了应用中需要注意的问题。最后以中国东部某浅海区二维资料为例进行了组合多重压制方法的试验。
多次波压制方法分为基于多次波和一次波的特征差异的滤波方法与基于波动方程的预测相减法。当假设条件较好地满足时,滤波方法能有效地压制多次波,且运算量较小,效率较高。但当多次波和一次波之间的特征差异很小或没有时,效果不好,甚至会严重损伤到一次波。预测相减法具有优异的振幅保真性,算法与速度无关,不需要或很少需要地下介质模型,用于压制自由表面多次波和层间多次波衰减研究。有很广的应用前景,但是它自身也有很多限制。通过应用试验表明,在压制多次波时,需要根据实际情况,选择合适的压制方法。对于多种类型的多次波发育的情况,单一方法很难有满意的效果,需要针对实际地震资料的特点,选择与资料相匹配的方法,通过扬长补短,优化组合,在保持有效反射的前提下,多重压制多次波。
中国东部某浅海区的应用试验表明,以τ-p域的预测反褶积和双曲线Radon变换为主的组合多重压制方案切实可行。由于具有独特的优点和广泛的适用性,有一定的推广价值和应用价值。
Multiple problems are prevalent in the seismic prospecting, especially in marine. Due to its complexity, multiple problems have not yet been solved well. As a kind of coherent noise, multiples can reduce S/N ratio of seismic data and disturb the reality and reliability of seismic imaging. So the suppression of multiples is critical important in seismic data processing. Therefore, multiple attenuation research has theoretical and practical significance.
Aiming at current research, the paper analyses some problems of multiple attenuation, discusses the cause, classification, kinematic characteristics, wave-field theory, and recognition of multiple respectively, and then discusses some common methods of multiple attenuation from different aspects including the principle, application conditions, advantages and disadvantages, and gives a great deal of application to test. Different from current and mainstream research, a combined multi-suppression's method for multiple attenuation is developed and applied.
Multiple attenuation methods can be classified into the filtering methods and the wave equation methods. The former is based on the differences of features or properties between multiples and primaries. By virtue of many advantages such as low cost and easy operation, it can suppress multiples effectively when the assumption is satisfied well. But once the differences are small or no difference, the former may serious injury primaries energy. The latter includes prediction and subtraction of multiples. Because of its algorithm with speed-independent and no or little need for the medium model, the latter is used in SRMA and IMA research. However, it also has many limitations.
The corresponding application tests show that, to select appropriate method for multiple attenuation is based on the actual situation of seismic data. When seismic data are in rich in various kinds of multiples, a combined method by optimizing several data-matching methods can suppress all multiples sufficiently while the primaries are kept well.
The suppression of multiples in shallow-sea data from eastern china shows that the combined multi-suppression's scheme based on predictive deconvolution inτ-p domain and hyperbolic Radon transform is feasible and effective. The combined scheme has a unique advantage and wide application potential.
引文
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