转换波成像方法综述

An overview about converted-wave Imaging method

中国石油天然气股份有限公司石油勘探开发研究院, 北京 100083

Institute of Petroleum Exploration & Development, CNPC, Beijing 100083, China

转换波勘探成本低,获取的地下信息量大。但由于转换波的传播路径不对称,入射波与反射波的速度不同,因此转换波资料的成像比纵波资料更复杂。为此,对转换波成像的主要方法进行了讨论,并对近年来出现的一些新的转换波成像思路作了介绍。转换波成像方法可分为叠后偏移和叠前偏移成像两种,叠后偏移主要包括共转换点道集抽取、动校正、转换波倾角时差校正和叠后偏移等,叠前时间偏移主要分为Kirchhoff叠前时间偏移和波动方程叠前时间偏移两大类。分别对叠后偏移的4个主要处理步骤和叠前偏移两类方法的基本原理进行了较为详细的阐述,并指出叠前时间偏移方法是目前转换波资料处理的发展方向。新的转换波成像思路是,先对转换波资料进行转换,然后再成像,如非对称性校正法和纯横波成像法等,对这些新方法的基本原理进行了论述。指出了转换波成像方法研究的发展方向,即转换波成像配套技术的研究如静校正、去噪,以及能更好地适应不同观测系统的高保真、高分辨率的叠前成像方法等。

The converted-wave is low in exploration cost and can obtain huge subsurface information. However, the travel path of converted-wave is asymmetric and the velocity of incident wave is different from that of reflected wave. So the imaging of converted-wave data is more complex than that of P-wave data. Aimed at this problem, the main methods of converted-wave imaging are discussed, and some new thoughts about PS wave imaging having been reported in recent years are introduced. The methods of converted-wave imaging can be divided into poststack migration and prestack migration. The poststack migration mainly includes common conversion point gather extraction, normal moveout correction, converted-wave dip movement correction and poststack migration while the prestack time migration is mainly divided into Kirchhoff prestack time migration and wave equation prestack time migration. The principles and advantages of each method are discussed in detail, showing that the prestack time migration is a trend of practical converted wave imaging. The new converted-wave imaging clue is that the converted-wave data are transformed first and then imaging, such as the asymmetry correction method and the unmixed s-wave imaging method, the principles of these new methods are discussed. The future direction of converted wave imaging is the research on supporting techniques of converted-wave imaging, such as the static correction, the noise pressing, the high-amplitude-pre-served and high-resolution pre-stack imaging method applicable for different geometries.