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偏移速度模型构建的精度,一直是叠前深度偏移成像结果好坏的关键。但是由于速度模型求取过程是由未知求未知的一个迭代过程,并且涉及到模型的建立、偏移和模型的修正等环节,这就要求我们针对问题的复杂性合理的描述速度模型。我们以Marmousi模型为研究的对象,根据模型不同速度的空间尺度,通过走时的变化和成像效果的对比分析,得出了以合理的尺度描述模型的一些依据,认为对于任何给定的地震数据集,在偏移速度模型中必须表现出的速度空间波长将随出现在该地震数据中的各种频率成分的空间波长而变,模型中描述速度场所必须的一些空间波长也将要随着地层的复杂性而变。对于简单的地层速度结构,采用一些简单的速度模型(具有很大的空间波长)也就足够了,对于复杂的地层速度结构,则需要更精细尺度的速度模型。但是实际建模过程中,我们很难全尺度的来描述模型。因此,在建模时,要根据模型的复杂程度,合理的限定描述模型参数的空间尺度,建立满足精度要求的宏观速度模型。
The accuracy of the migration velocity model building has always been the key to good or bad pre-stack depth migration imaging. However, because the speed model retrieval process is an iterative process of unknown unknown, and involves the establishment of the model, the offset and the modification of the model, which requires that we describe the speed model reasonably according to the complexity of the problem. Based on the Marmousi model and the space scale of different velocities of the model, we draw some evidences for describing the model at a reasonable scale by analyzing the change of travel time and the imaging effect. It is considered that for any given seismic data set , The velocity spatial wavelength that must appear in the migration velocity model will vary with the spatial wavelength of the various frequency components present in the seismic data and some of the spatial wavelengths necessary to describe the velocity regime in the model will also vary with the complexity of the formation Sexual change. For a simple formation velocity structure, it is sufficient to use some simple velocity models (with large spatial wavelengths), and for complex formation velocity structures, a more precise velocity model is needed. However, in the actual modeling process, it is difficult to describe the model on a full scale. Therefore, in modeling, according to the complexity of the model, the spatial scale describing the model parameters should be reasonably limited, and the macro-speed model meeting the accuracy requirements should be established.