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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.
Accurately extracting the Q value is the key to studying the absorption and attenuation characteristics of the strata.The contrastive analysis of the three Q inversion methods (centroid frequency method, amplitude attenuation method and spectrum ratio method) is designed to provide reference for the attenuation characteristics. The results show that the accuracy and the difference of Q value inversion and horizon reveal under the conditions of thin layer, bandwidth, low attenuation layer, wave field composition and interface interference are as follows: For relatively thin layers , The centroid frequency method can reveal almost all strata accurately, while the other two methods show anomalies at the interface of the thin layers with an error of more than 200%. The high frequency components have a great influence on the frequency domain method, especially for the inversion of low attenuation layers The calculated results of the three methods are similar only in the down / up-going wavefields, and the center-of-mass-frequency method in the full-wavefields works well. The existence of the reflecting interface will cause interference to the three methods and the inversion value jumps at the interface. In the actual application of VSP data, we know that the Q-value stratification is more sensitive than the velocity curve, and the inversion of the Q value of the centroid frequency method is the best one to the geological stratification.