克希霍夫叠前深度偏移在川东地区的应用

Application of Kirchhoff PSDM to seismic data in north east of the Sichuan Basin

常规叠前深度偏移方法都是将数据延拓到最终面,然后从固定面偏移.在川东复杂山区,地形起伏大,地表切割剧烈,表层结构复杂,地腹构造褶皱剧烈,逆冲断层发育,地震波传播纵横向变化大,如果把数据校正到固定面来偏移,势必带来很大误差,严重影响射线追踪的准确性.另外由于该地区勘探程度较低,钻井资料很少,失去了建立偏移速度场的重要约束条件.为此针对该地区,本文提出了一种利用时间域资料约束的多模式速度-深度模型建立及分析技术,并应用基于浮动地表的Kirchhoff叠前深度偏移技术对川东某工区实际地震资料进行了处理.在该工区的应用表明,这两种技术很好解决了起伏地表的问题,对复杂地质体有较强的适应性,并且在有限钻井资料情况下,也能快速高效建立精确偏移速度场.最终偏移后的结果跟叠后时间偏移处理的结果相比归位精度得到显著提高,断层断点更为清楚,而且过井深度偏移剖面与钻井深度对比吻合也比较好,在井深度对比中各层误差均小于50m,各层深度误差小于1%,为后续的地质研究提供了很好的资料.

Conventional pre-stack depth migration methods need to correct all the data to a fixed datum, then migration from the fixed datum. North east of Sichuan mountainous area has dramatic changing topography, complex seismic geological conditions, and greatly varied lateral and vertical velocity. Therefore, if we correct data in this area to a fixed datum, it may produce a lot of errors, and affect the accuracy of. ray tracing. Furthermore, because of low level of exploration, it has very limited well information in this area, therefore it lost the most important constraint for establishing an accurate migration velocity field. In this paper, we introduce the technology of a multi-mode building depth-velocity model by using time domain data as constraint, and process the data with the method of Kirchhoff pre-stack depth migration from floating datum. The application of these two technologies in this area demonstrate that they are good solutions to resolve the problem of changing topography, and they also can adapt the complex geological body. When we don＇t have adequate well information, we still can use them to efficiently build the accurate migration velocity field. The most important thing is we obtain a much better image compared to the post-stack time migration method. Moreover the horizon depth in pre-depth migration section is in agreement with the measuring depth of the well. The differences between them are less then 50m, and the errors between them are less then 1%.