Seismic diffraction imaging by reverse time migration in dip angle domain
WANG Tianchi1,2, LIU Shaoyong1,2, GU Hanming1,2, TANG Yongjie1,2, YAN Zhe1,2
1. Institute of Geophysics and Geomatics, China University of Geosciences(Wuhan), Wuhan, Hubei 430074, China; 2. Hubei Subsurface Multiscale Imaging Key Laboratory, Wuhan, Hubei 430074, China
摘要 地下缝洞型储层及非规则矿体的地震响应表现为绕射波，在成像域倾角道集中进行反射波压制，有利于这些目标体绕射波成像。利用逆时偏移（Reverse Time Migration，RTM）和Kirchhoff积分偏移分别进行倾角道集的提取，在倾角域分析两种典型成像方法对绕射波的成像能力。研究表明，在倾角域RTM比Kirchhoff积分偏移算子具有更强的反射波聚焦能力，有利于成像过程中对反射波的压制。具体而言，采用波印廷矢量方法在RTM过程中进行倾角道集输出；在RTM提取的倾角道集中反射波能量聚焦为孤立的“噪点”，绕射波则表现为一条拉平的直线。基于两者形态的差异，在倾角域进行中值滤波能有效分离绕射波与反射波，进而实现RTM绕射波成像。数值实验结果验证了文中方法的正确性和有效性。
Abstract：The seismic responses of fracture-cavity reservoirs and irregular orebodies are characterized by diffractions.Reflected wave suppression during seismic migration in dip-angle domain is beneficial to imaging these targets.We used Kirchhoff migration and reverse time migration (RTM) to extract dip-angle gathers,and then compared their imaging performances based on diffractions.The results shows that RTM has a better reflections focusing ability than a Kirchhoff migration operator in dip-angle domain,and makes reflections suppression much easier. The Poynting vector method is introduced in our study to produce the dip-angle gather during the RTM process. Among the dip-angle gathers extracted by RTM,the energy of reflections focus on isolated “noises”,but diffraction events appear as a flattened straight line.Based on the difference in their responses,suppressing “noises” with median filtering can separate diffractions from reflections,and consequently RTM diffraction imaging to get good results.Numerical experiments have verified the correctness and effectiveness of the method proposed.
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