层状介质时移时差的分析研究

Analysis of time-lapse seismic time difference in layered strata

时移地震时差是时移地震研究的关键问题之一 ,它包含了储层的层速度差异信息 ,而层速度差异反映了储层流场的变化。由于地震勘探频率低 ,用地震资料确定时移地震的时差非常困难。目前 ,时移时差的研究基本上使用叠后资料 ,用叠前资料研究时移时差的报道还未见过。对于单层介质 ,用叠前远偏移距的时差 (可测量 )可以计算出垂直时差 ;对于层状介质 ,油藏变化前后的地震波传播路经比较复杂 ,其激发点和接受点发生了变化 ,要想用叠前远偏移距数据直接计算垂直时差比较困难。以双层介质为例 ,对层状介质的时差进行了推导和研究 ,得出了十分有价值的结论 。

Time lapse seismic time difference is very important for it shows the interval velocity difference, and the interval velocity difference depicts the changes of fluid field in strata. But it is difficult to determine time lapse seismic time difference by seismic data for its low frequency. At present, post stack seismic data is used in China for the study of time difference,the study using pre stack seismic data has not been reported. To single stratum, vertical time difference can be computed using time difference of pre stack far offset seismic data. But to layered strata, the seismic wave path is complicated when reservoir changes, and it is difficult to directly define vertical time difference by pre stack far offset seismic data. In this paper, valuable results are concluded by the study of double strata, and the conclusion is useful to the development of time lapse seismic.