基于模型正演的叠前深度偏移

FORWARD MODELING-BASED PRE-STACK DEPTH MIGRATION

川西龙门山前缘构造非常复杂,逆掩推覆构造带构造形变强烈,构造幅度大,地层倾角陡,断块发育,波场复杂,速度横向变化大,常规叠后时间偏移处理成像效果较差。文章将地震资料模型正演技术应用到叠前深度偏移,探讨了一种有助于川西龙门山前缘逆掩推覆构造地震资料精确成像技术。先利用已有地震资料解释成果,根据地质任务建立二维地质模型,在此基础上进行射线追踪、模拟出单炮地震记录和自激自收剖面,从而对观测系统的最大炮检距、道间距等参数进行论证的一些实用方法,这些方法对地震资料采集具有很好的指导作用;然后根据这些结果,再比较准确地进行叠前深度偏移的初始速度模型建立,从而达到了复杂地表下复杂构造精确成像的目的。

The front structures of Longmen Mountain in the western Sichuan Basin are very complex. The overthrust nappe structural zone is characterized by strong tectonization, large structure amplitude, deep stratigraphic dip, well developed fault blocks, complicated wave field and large lateral change of velocity, resulting in poor imaging of conventional post-stack time migration. In this paper, forward modeling technique is applied to pre-stack depth migration to accurately image the front overthrust nappe structure of Longmen Mountain in the western Sichuan Basin. According to the geologic task, a 2D geologic model is first built by using the available seismic interpretation results. Single shot seismic record and self-shooting—self-receiving profile are obtained through ray tracing and simulation. Several practical methods are presented to determine the parameters of observation system such as the maximum offset and group interval. These methods can well guide seismic acquisition. An accurate initial velocity model for pre-stack depth migration is built by using these parameters to accurately image the complex structures with complex surface conditions.