共中心点道集偏移速度分析

Migration velocity analysis of common mid point gathers

1. 石油大学资源系,东营257062;2. 同济大学海洋地质与地球物理系,上海200092

Department of Resources, University of Petroleum, Dongying 257062

偏移速度分析是叠前深度偏移的关键步骤之一,它的准确与否直接影响叠前深度偏移的质量。考虑到效果和计算效率,本文提出了一种利用射线追踪进行速度扫描的共中心点(CMP)道集偏移速度分析方法,它适用于层状介质和连续介质,不受上覆地层的复杂性、横向变速、地层倾角和炮检距大小的影响。经模型试算,浅、中层速度误差小于1%～1.5%,深层小于2%～3%,反射层深度总体误差小于20m,薄互层分辨率可达半个有效地震子波长度。

Migration velocity analysis is one of the key steps in pre stack depth migration whose accuracy directly affects the quality of pre stack depth migration. Taking account of the result and computational efficiency, we put forward a method in which migration velocity analysis is realized by velocity scanning using ray tracing in common mid point (CMP) gathers in this paper. It applies to layered and continuous media,not affected by complicated overburden, laterally variable velocity, steep dip and large offset. Theoretical models show that velocity error is less than 1%～1.5% in shallow and median layers and 2%～3% in deeper layers, reflector depth error is less than 20 m,and thin bed resolution reaches the half effective wavelet length.