An improved fast converted-wave imaging method

一种改进的转换波快速成像方法研究（英文）

The conventional fast converted-wave imaging method directly uses backward Pand converted S-wavefield to produce joint images. However, this image is accompanied by strong background noises, because the wavefi elds in all propagation directions contribute to it. Given this issue, we improve the conventional imaging method in the two aspects. First, the amplitude-preserved P-and S-wavef ield are obtained by using an improved space-domain wavef ield separation scheme to decouple the original elastic wavef ield. Second, a convertedwave imaging condition is constructed based on the directional-wavefield separation and only the wavefields propagating in the same directions used for cross-correlation imaging, resulting in effectively eliminating the imaging artifacts of the wavefields with different directions;Complex-wavefi eld extrapolation is adopted to decompose the decoupled P-and S-wavefield into directional-wavefields during backward propagation, this improves the eff iciency of the directional-wavef ield separation. Experiments on synthetic data show that the improved method generates more accurate converted-wave images than the conventional one. Moreover, the improved method has application potential in micro-seismic and passive-source exploration due to its source-independent characteristic.

常规转换波快速成像方法直接利用反传的纵波和转换横波进行联合成像,由于所有传播方向的波场均参与转换波成像,导致成像剖面存在大量背景干扰噪声。针对这一问题,本文从以下两个方面对常规方法进行改进。一方面,本文采用改进的空间域波场分离方法对原始弹性波场解耦,得到保幅的纵、横波场。另一方面,构建了基于方向行波分离的转换波成像条件,在成像过程中只利用同向传播波场进行互相关成像,有效消除了不同方向传播波场的成像假象;为了提高方向行波分离的效率,在波场反传时采用复数波场延拓技术对解耦的纵、横波场进行方向行波分离。模型试算结果表明,改进后的方法转换波成像精度高于常规方法。而且,由于其与震源无关的特性,该方法还具有在微地震及被动震源勘探中的应用潜力。