层状介质时移时差研究

由于叠后资料相当于零偏移距资料，而零偏移距的时移时差很小，因此直接用叠后资料研究时移时差很困难。笔者提出采用叠前远偏移距数据来求取时移地震时差。据多层理论模型计算时差的数量级可达10ms以上。但是，对于层状介质，油藏变化前、后的地震波传播路径比较复杂，其激发点和接收点发生了变化，要想用叠前远偏移距数据直接计算垂直时差比较困难。本文以双层介质为例，对层状介质的时差进行了推导和研究，认为采用较大的入射角所产生的时移时差可以较准确地求出油藏流体替换后的速度差，从而达到用四维地震进行油藏监测的目的。

Time difference of time-lapse in layered medium.

It's difficult to directly use poststack seismic data for studying time difference of time lapse because the poststack seismic data corresponds to zero offset data and the time difference of time lapse is very small.The authors presented adopting prestack seismic data on far offset to calculate the time difference of time lapse.The order of time difference by finely calculation for multi layered theoretical model can be reached to 10 ms and above.But for a layered medium,it's difficult to compute the vertical time difference directly by using prestack data on far offset because the travelling paths of seismic wave before and after the reservoir variation are very complex and shot points and receiver points are changed.Taking a double layered medium as an example,the paper deduced and studied the time difference of layered medium,considered that using time difference of time lapse produced by large incident angle can accurately calculate the velocity difference produced by replaced reservoir fluid,which attained the goal by using 4 D seismology to monitor the reservoir.