强衰减地层VSP反Q滤波方法

VSP inverse Qfiltering in strong attenuation formations

本文根据零井源距VSP下行初至波最大振幅随时间的变化趋势,将地层划分为强衰减地层和弱衰减地层。其中地震波衰减最强烈的强衰减地层可认为是由多个层状常Q介质构成,Q值主要利用VSP资料提取;而弱衰减地层认为是Q值大于200、地震波发生的衰减相对较弱甚至可以忽略的地层。在波场延拓反Q滤波方法基础上本文提出VSP强衰减地层反Q滤波,该法弥补了因中、深层Q值难以求准、补偿约束难度较大等因素导致的反Q滤波精度降低的缺陷,使反Q滤波结果更稳定、高效,也为地面地震反Q滤波方法的完善及应用提供有意义的启示。

VSP is used to study seismic absorption and attenuation because of seismic wave acquired in wells.We consider that there are two kinds of formation:strong attenuation formations and weak attenuation formations according to the maximum amplitude variation of down primary wave with time in zero-offset VSP.The strongest attenuation formation is composed by multi constant Qlayers,and the Qvalue in each layer can be extracted from VSP data.While the Qis infinite in weak attenuation formations,and seismic wave attenuation can be ignored.Based on the wave-extrapolation inverse Qfiltering,the inverse Qfiltering in strong attenuation formations is presented in this paper.Pilot tests show that this proposed approach is more stable and efficient than conventional inverse Qfiltering which lead low accuracy due to difficulties in accurate Qvalue calculation.At the same time,this approach may provide meaningful insights for surface seismic inverse Qfiltering.