大井源距VSP记录的波场异常剖析

Analysis of wave-field abnormality of big offset VSP data,

加大井源距可以扩大VSP资料的成像范围,提高VSP测井的实用价值,但与此同时又会导致两个严重的后果:①VSP原始记录出现某些波场异常;②VSP-CDP转换的拉伸畸变加大。本文从NU34井VSP记录实例出发,着重剖析第一个问题,即大井源距与VSP记录中的初至异常和波组干涉之间的因果关系,并就如何避免波场异常及对最大井源距参数的施工设计提出参考意见。

Bigger offset results in wider VSP image extent and better VSP application. However, there follow two disadvantages: some wavefield abnormality of raw VSP data and increased stretching distortion in VSP-CDP transformation. The causal relation between big offset and VSP first-arrival abnormality or wave group interference is analysed using the VSP data from well NU34. Suggestions on avoiding wave-field abnormality and designing optimum VSP offset are made by the authors