Crosshole seismic waveform tomography – I. Strategy for real data application
Crosshole seismic waveform tomography – I. Strategy for real data application
复制标题
DOI：
10.1111/j.1365-246x.2006.03030.x
复制
发表时间：
2006-09
影响因子：
2.8
通讯作者：
Yanghua Wang;Y. Rao
中科院分区：
文献类型：
--
作者：
Yanghua Wang;Y. Rao
波形层析成像的频域版本可以使用不同的频率分量来充分重建地下速度场，从而大大减少了反演过程所需的输入数据量。这使得波形层析成像在生产应用中成为一个计算上易于处理的问题，但它对实际地震数据的适用性，特别是在石油勘探和开发规模上的适用性，还需要进一步研究。由于实际数据往往是带限的，缺少低频，因此波形层析成像需要一个好的起始模型，在可用频率反演之前填补低频的空白。在反演阶段，每次迭代应同时使用一组频率，以抑制频域数据噪声的影响。同时，在反演过程中必须对模型进行平滑约束，以应对数据噪声的影响、问题的非线性影响以及短波模型变化的强灵敏度影响。在本文中，我们使用频域波形层析成像技术来提供井间目标300 m的定量速度图像。由于当地地质的复杂性，速度变化非常极端（在3000 ~ 5500 m s - 1之间），使得反演问题高度非线性。尽管如此，波形层析成像结果与井眼测井结果吻合良好，并提供了真实的地质信息，可以可靠地在井眼之间进行跟踪。
SUMMARY The frequency-domain version of waveform tomography enables the use of distinct frequency components to adequately reconstruct the subsurface velocity field, and thereby dramatically reduces the input data quantity required for the inversion process. It makes waveform tomography a computationally tractable problem for production uses, but its applicability to real seismic data particularly in the petroleum exploration and development scale needs to be examined. As real data are often band limited with missing low frequencies, a good starting model is necessary for waveform tomography, to fill in the gap of low frequencies before the inversion of available frequencies. In the inversion stage, a group of frequencies should be used simultaneously at each iteration, to suppress the effect of data noise in the frequency domain. Meanwhile, a smoothness constraint on the model must be used in the inversion, to cope the effect of data noise, the effect of non-linearity of the problem, and the effect of strong sensitivities of short wavelength model variations. In this paper we use frequency-domain waveform tomography to provide quantitative velocity images of a crosshole target between boreholes 300 m apart. Due to the complexity of the local geology the velocity variations were extreme (between 3000 and 5500 m s −1 ), making the inversion problem highly non-linear. Nevertheless, the waveform tomography results correlate well with borehole logs, and provide realistic geological information that can be tracked between the boreholes with confidence.