零偏VSP反演Q值CFS方法及影响因素研究  

Study on CFS method in Q inversion using zero-offset VSP data

作　　者：武银婷[1] 朱光明[2] 刘伊克[1] 常旭[1] 

机构地区：[1]中国科学院地质与地球物理研究所,北京100029 [2]长安大学,西安710054

出　　处：《地球物理学进展》2010年第6期1897-1904,共8页Progress in Geophysics

基　　金：国家重点基础研究发展计划(2009CB219404)资助

摘　　要：当地震波在地层中传播时,能量的衰减是传播介质非弹性性质的反映.这种介质所固有的衰减特性通常用品质因子(Quality Factor,Q)来描述.本文基于地震波在传播过程中主频降低的衰减特性,利用质心频率偏移法(Centrold Frequency Shift,简称CFS)对零偏VSP正演模型进行Q值计算,分析薄层、上下行波场、频带宽度、反演波速、震源位置等因素的影响.模型结果显示:CFS法比频谱比法、振幅衰减法能更加准确识别薄层界面,可准确反演出厚度10m的地层;上行波场的加入降低反演结果准确度,尤其对高Q值层;当有效波频带增宽时,高频部分衰减明显,Q值反演结果接近理论值;反演波速误差对反演准确性影响很大.最后,利用CFS对实际井旁地面地震资料进行Q值反演,反Q滤波后其主频由25Hz提高到35Hz,分辨率得到改善,证明了CFS方法的实用性.Energy attenuation is the reflection of non-elastic property when seismic wave propagates in the medium, which is usually represented by Quality Factor, Q for short. As higher frequency attenuates more quickly than lower one, based on the centroid frequency receding in the propagation, the Centroid Frequency Shift method （CFS for short ） is used to inverse the Q value on the forward zero-offset VSP geological model. Some factors that influence this method＇s application results are discussed, including the thin layer, down-going wave and up-going wave, frequency bandwidth, velocity to inverse and locations of sources. The calculations of several models show that the CFS method is much more accurate in inversion of the Q value and can reveal boundaries of thin layers, even a layer of 10m thickness. The joined up-going wave influences the inverse effect, especially to high Q layers. And the broadening of bandwidth can apply more space to attenuate higher frequency, so it ought to improve the accuracy, up to the theoretical value of Q. The deviation of velocity used to inversion can greatly bring in errors, which should attract attention. While, in order to check the effect of CFS method on the field material, zero-offset VSP data and its nearby ground seismic data are chosen. After the inverse Q-filtering, its main frequency ascends from 25Hz to 35Hz and the resolution of section is ameliorated, which can illustrate CFS methodrs utility somewhat.

关 键 词：零偏VSP 衰减 Q值 质心频率 CFS 

分 类 号：P315[天文地球—地震学]