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| Reverse time migration in VTI media based on wavefield decomposition |
| Xu GUO, Jian-Ping HUANG, Zhen-Chun LI, Jin-Qiang HUANG, Feng ZHU |
| School of Geosciences,China University of Petroleum (East China),Qingdao 266580,China |
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Abstract Seismic anisotropy characterized by velocity anisotropy will inevitably affect the kinematic characteristics of underground seismic waves.Ignoring the anisotropy of the media will result in inaccurate velocity extraction and thus affect the imaging of target region.In view of such a situation,the authors carried out a study of anisotropy in this paper.According to the first-order velocity stress equation in VTI media,the authors obtained the cross-correlation imaging condition based on wavefield separation which used Poynting vector.Then the authors applied it to complex VTI media,and demonstrated the validity and superiority of the algorithm by numerical experiments.This method produces better images with less noise even for inaccurate migration velocities.
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Received: 23 March 2018
Published: 20 February 2019
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The homogeneous model
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Seismic snapshot and corresponding Poynting vector at 400 ms
a—snapshot;b—horizontal component;c—vertical component
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Seismic directional wave separating snapshots at 400 ms
a—up-going wave snapshot;b—down-going wave snapshot;c—left-going wave snapshot;d—right-going wave snapshot
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A three-layer model
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Comparison of imaging results under different imaging conditions for the three-layer model
a—Iuu(x,z);b—Idd(x,z);c—Iud(x,z);d—Idu(x,z);e—I(x,z);f—the difference between figure e and figure d
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The SEG/EAGE salt model
a—true velocity model;b—migration velocity model
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Reverse time migration imaging results of SEG/EAGE salt model
a—conventional cross-correlation VTI-RTM;b—figure a after filtering;c—directional wave separation VTI-RTM;d—figure c after filtering;e—directional wave separation Isotropic-RTM;f—figure e after filtering;g—the difference between figure a and figure c
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Magnified view of the white rectangular frame on top of the salt
a—magnified view of the figure 7b;b—magnified view of the figure 7d
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Magnified view of black rectangular frame inside the salt
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| 偏移方法 | 计算量 | 平均每炮计算时间/s | | 常规互相关VTI-RTM算法 | $\partial$σxx/$\partial$x,$\partial$σzz/$\partial$z,$\partial$vx/$\partial$x,$\partial$vz/$\partial$z | 1398.53 | | 本文行波分离VTI-RTM算法 | $\partial$σxx/$\partial$x,$\partial$σzz/$\partial$z,$\partial$vx/$\partial$x,$\partial$vz/$\partial$z,σzzvz | 1571.14 | | 本文行波分离各向同性RTM算法 | $\partial$p/$\partial$x,$\partial$p/$\partial$z,$\partial$vx/$\partial$x,$\partial$vz/$\partial$z,pvz | 1537.28 |
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Computational efficiency comparison of different migration methods for SEG/EAGE salt model
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Inaccurate migration velocity model
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Comparison of imaging results with 3% error in velocity
a—conventional method;b—our method
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