基于零偏VSP三种Q值反演方法对比分析及应用

Comparison and application of three different methods for inversing Q value with zero-offset VSP data

准确提取Q值是研究地层吸收衰减特性的关键.对三种Q值反演方法(质心频率法、振幅衰减法、频谱比法)进行对比分析,旨在为衰减特性的求取提供参考.针对零偏VSP数据进行计算,对比总结薄层、频带宽度及低衰减层、波场成分、界面干扰等条件下Q值反演与层位揭示的准确性及差异性:对于相对较薄的层位,质心频率法几乎能准确揭示所有地层,而其他两种方法在薄层分界面处出现异常,误差超过200%;高频成分对频率域方法影响较大,尤其是对于低衰减层的反演;只有下/上行波场时三种方法计算结果相似,全波场时质心频率法效果较好;反射界面的存在会对三种方法造成干扰,反演值在界面处出现跳跃.对比分析三种方法在实际VSP数据应用可知:Q值分层比速度曲线更为敏感,质心频率法Q值反演曲线与地质分层吻合程度最好.

This paper elaborates three different methods,including centroid frequency shift（ CFS） method, amplitude attenuation method and spectral ratios method to inverse quality factor value（ Q）,which is the attenuation characterization. Contrasting on the results from series of zero-offset VSP model data,we discuss several factors to influence the inversion,including thin layers,frequency ranges,low-attenuation layers,different waveform components,and the interface interferences. We find that CFS method is more stable and accurate to layers with high Q value,interface interference,different waveforms, while, other two methods get deviation.Specifically,amplitude attenuation method has the least stability,while,compared with other two methods,CFS is the most powerful to anti interface interferences with the minimum fluctuates;Furthermore,from the application of three methods to field VSP data we can see that,the curve from CFS is consistent with lithologic core best and can reveal depths of each layers better than corresponding velocity curve,however,the other two methods just can show the main trend of Q values with poorly accuracy.