基于源波场照明的逆时偏移振幅补偿方法研究

逆时偏移作为一种先进的地震成像方法，能够适应横向变速和高陡倾角等复杂地质构造成像。但在对逆掩断层等复杂地质构造进行逆时偏移成像时，由于断层对地震波场的屏蔽效应，导致其下盘地质构造成像振幅很弱。一般采用单炮源波场照明除互相关成像来对深层构造弱振幅成像进行补偿，这种单炮源波场照明补偿方法虽然简单，但在地质构造特别复杂时会导致波场照明空间变化剧烈，从而影响成像振幅的补偿效果，加重了背景假像和噪音。为了克服这一问题，本文提出均炮源波场照明补偿方法，即用均炮源波场照明除互相关成像来进行弱振幅补偿，均炮源波场照明是指利用某一炮附近邻域内所有单炮源波场照明的均值来代替该炮源波场照明。对于复杂构造，由于均炮源波场照明空间变化较平缓，在进行逆时偏移成像振幅补偿时，背景假像和噪音也能得到很好地压制。根据实际地质构造设计了一个逆掩断层理论模型来验证均炮源波场照明振幅补偿的效果，并和单炮源波场照明振幅补偿进行了对比。

Reverse time migration amplitude compensation based on source illumination

As an advanced seismic imaging method, reverse time migration (RTM) can adapt to the complex geological structures with large lateral velocity variation and high dip angle. But in the implementation of RTM of complex geological structures, such as overthrust, because of the shielding effect of the fault on the seismic wavefield, the imaging amplitude of the footwall geological structure is very weak. Generally, the method that the cross-correlation image divided by single-shot source illumination is used to compensate the weak amplitude in the RTM of the deep complex geological because of its simplicity. But it will lead to the large spatial variation of the source illumination for too complicated geological structures. It results in the increasement of the background artifacts and noise, which affects the final imaging quality. In order to overcome this problem, we propose the amplitude compensation method based on the mean-shot source illumination, which divide the cross-correlation image by the mean-shot source illumination. The mean-shot source illumination is to use the mean of all single-shot source illumination in the neighborhood of one shot to replace the single-shot source illumination. For the complex structures, the spatial variation of the source illumination is relatively smooth and the false image and noise can be suppressed well. According to the actual geological structure, a theoretical model of the overthrust is designed to verify the compensated effect of the weak amplitude based the mean-shot source illumination, and compared with that of the single-shot source illumination.