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2 Acta Geophysica

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An efficient low-frequency artifact suppression method at excitation time for excitation amplitude imaging condition

100%

Wang R. , Wang D. , Hu B. , Zhang W. , Zhou J. , Li B.

tom Vol. 71, no. 3

1225--1240

The excitation amplitude imaging condition (EAIC) is a high-resolution, computationally efficient, and low-storage imaging condition in reverse time migration (RTM). However, when there are strong reflection interfaces in the velocity model, they will produce low-frequency artifacts, which seriously contaminate the RTM image. The artifacts can be removed by the wavefield decomposition algorithm, but this process always performed by analytic time wavefield extrapolation, which needs extra wavefield extrapolation. Furthermore, an extra source wavefield extrapolation is required to determine the excitation time before the migration. Thus, the additional wavefield extrapolations can seriously damage the computationally efficient advantage of the EAIC. By taking advantage of the directivity and low storage of excitation amplitude, we present a low-frequency artifact suppression method with no extra wavefield extrapolation. Poynting vector, reference traveltime and minimum amplitude threshold are combined to constraint the excitation amplitude updating process, and it makes the excitation amplitude more consistent with the definition of excitation criterion. We can directly obtain a noise-free excitation amplitude without the source wavefield decomposition. Instead of the analytic time wavefield extrapolation, the time-bin technique and the windowed Hilbert transform are combined to achieve the receiver wavefield decomposition only at the excitation time. The numerical results show that our method can effectively suppress the low-frequency artifacts in the image with no extra wavefield extrapolation.

Target-oriented reverse time migration in transverse isotropy media

100%

Song L. , Shi Y. , Chen S. , Wang W. , Ke X.

tom Vol. 69, no. 1

125--134

Reverse time migration (RTM) is a high-precision imaging method for complex structures. However, without considering seismic anisotropy of the subsurface, RTM utilizing the anisotropic seismic data may produce blurred structure images with incorrect positions. Moreover, some exploration targets with insufcient illumination cannot be efectively identifed in the migration profle, especially the subsalt structure which is usually the favorable petroleum region for the hydrocarbon reservoir. Therefore, we develop a target-oriented RTM in transverse isotropy media (TO-TIRTM). Instead of classical RTM, the novel method extracts wavefelds that carry relatively more information about the exploration target to image structure. In the imaging condition, the constraint with excitation time is introduced to eliminate the interference of multipath on the image. Using synthetic examples, we determined that the kinematic characteristic of wavefeld is closely related to aniso tropic parameters, and the proposed method has prominent advantages over conventional RTM for imaging insufcient illumination structure.