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提出了一种混合波动方程走时和波形反演方法,它可以根据井间地震资料重建层速度分布。这种反演方法(简称为WTW法)包含了全波反演和走时反演的优点;例如,它具有与初始模型无关并快速收敛的特点,并且还能解释速度模型的具体特征。理论上,不必拾取走时,从而WTW方法所耗费的机时大致与全波反演相当。我们运用WTW方法处理了Exxon得克萨斯Friendswood试验场地采集的合成资料和野外井间资料,结果表明,WTW层析图象比走时层析图象在构造信息方面要丰富得多。在WTW Friendswood层析图象上可分辨出1.5 m的微小构造,而在走时层析图象上却模糊不清,甚至完全没有反映。这表明,在中频段它可以较好地获得高质量(反射清楚)的井间资料,在高频段只能得到中等质量的资料(初至质量好,但反射波充满噪声)。重建的速度剖面和震源井的资料对比表明,在0～200 m的间距内两者吻合得很好;在200～300 m间距内,速度变化趋势基本一致,但是层析图象上的速度剖面不同于模-数转换的声波测井速度。这就强调了WTW法既有较成功的一面又存在着一定难度的一面,它能重建模型的中、高波数部分,但是它却难以恢复模型的低波数部分。
A time-varying and waveform inversion method for mixed wave equation is proposed, which can reconstruct the velocity distribution of the layer based on the crosswell seismic data. This inversion method (referred to as the WTW method for short) contains the advantages of full-wave inversion and travel-time inversion; for example, it has the characteristics of being fast convergent regardless of the initial model and also explaining the specific features of the velocity model. Theoretically, it is not necessary to pick up the travel time, so the WTW method consumes about the same time as the full-wave inversion. We used the WTW method to process synthetic data and field cross-bore data collected at the Exxon, Friendswood, Texas test site. The results show that the WTW tomographic images are much more plentiful in constructing information than walking-time tomographic images. Small structures of 1.5 m can be discerned on the WTW Friendswood tomographic image, but are vague or even completely unrecognizable in the time-lapse tomographic image. This shows that it is possible to obtain good quality (well-reflected) cross-well data in the mid-band and only moderate-quality data in the high frequency band (good first arrival but full reflected noise). The reconstructed velocity profile and source well data show that the two agree well with each other in the interval of 0 ~ 200 m. The trend of velocities in the interval of 200 ~ 300 m is basically the same. However, the velocity profile on the tomographic image Sonic logging speed different from A / D conversion. This emphasizes that the WTW method has both the more successful and the more difficult aspects. It can reconstruct the middle and high wavenumber of the model, but it is hard to recover the low wavenumber of the model.