基于优化交错网格有限差分法的VSP逆时偏移  

Reverse time migration of VSP data based on the optimal staggered-grid finite-difference method

作　　者：刘炜 王彦春[2] 毕臣臣 徐仲博 LIU Wei;WANG Yan-Chun;BI Chen-Chen;XU Zhong-Bo(Post-doctoral Research Station of Geophysics,Chengdu University of Technology,Chengdu 610059,China;School of Geophysics and Information Technology,China University of Geosciences,Beijing 100083,China)

机构地区：[1]成都理工大学地球物理学博士后科研流动站,四川成都610059 [2]中国地质大学(北京)地球物理与信息技术学院,北京100083

出　　处：《物探与化探》2020年第6期1368-1380,共13页Geophysical and Geochemical Exploration

基　　金：中国石化科技发展部项目“沉积模式约束岩相和流体反演方法研究”(P18070-6)。

摘　　要：相比于常规地面地震资料,VSP地震数据具有波场信息丰富、分辨率和信噪比高等优点;逆时偏移方法基于双程波波动方程,被认为是目前成像精度最高的地震资料偏移成像方法,二者相互结合,有利于精确刻画井旁构造以及识别地下复杂地质构造。本文从二维变密度声波波动方程入手,研究基于优化交错网格有限差分法的VSP数据高精度逆时偏移方法。针对逆时偏移的不同方面,采用优化交错网格有限差分法进行高精度波场延拓,采用PML吸收边界条件压制由人工截断边界造成的边界反射,采用有效边界存储策略降低波场存储需求,采用震源归一化零延迟互相关成像条件进行高精度成像,采用高阶拉普拉斯滤波方法压制低频成像噪声。模型测试结果表明:本文方法能够实现VSP数据的高精度逆时偏移成像,相比于常规地面地震数据的逆时偏移,VSP数据的逆时偏移能够更加精确地识别如高陡构造、速度变化剧烈构造等地下复杂地质构造,验证了方法的有效性。Compared with conventional surface seismic data,VSP seismic data have many advantages,such as abundant wavefield information,high resolution and signal-to-noise ratio information.Reverse time migration(RTM)method based on two-way wave equation is considered to be the most accurate imaging method for seismic data at present.The combination of the VSP data and RTM method is helpful to describing the structures beside wells and identifying the complex geological structures accurately.Based on the two-dimensional(2D)variable density acoustic wave equation,the authors studied the high-precision RTM method of VSP data using the optimal staggered-grid finite-difference method.For different aspects of this VSP RTM method,different measures were adopted.First,the authors used the optimal staggered-grid finite-difference method to realize high-precision wavefield extrapolation.Second,the authors used the PML absorbing boundary condition to suppress boundary reflections caused by the limited computing space of model.Third,the authors used the effective boundary storage strategy to reduce the storage requirements of source wavefields.Fourth,the authors used the normalized cross-correlation imaging condition of sources to handle RTM imaging of VSP data.Finally,the high-order Laplacian filtering method was used to suppress the low-frequency noises of RTM imaging results.The different model test results show that the VSP RTM method proposed in this paper can achieve high-precision RTM imaging for VSP data.Compared with the conventional RTM method of surface seismic data,the RTM method of VSP data can more accurately identify the underground complex geological structures,such as the high-steep structures and the structures with sharp velocity changes,which verifies the effectiveness of the proposed method.

关 键 词：VSP 优化交错网格有限差分法 逆时偏移 存储策略 噪声压制 

分 类 号：P631.4[天文地球—地质矿产勘探]