一次反射波与自由表面多次波联合偏移成像:模拟数据分析

Simultaneous migration of primary and free surface multiples: modeling data analysis

基于逆时偏移互相关成像条件,一次反射波与自由表面多次波联合偏移成像可以提供更宽的地下照明成像,以弥补一次反射波覆盖不足,同时不需要预测分离多次波,但是,在成像过程中也引入了偏移假象。首先对一次反射波与自由表面多次波联合偏移成像条件进行分析,通过对模拟数据成像结果分析,提出利用多次波信息进行成像,需要用震源子波和相位反转的地震记录作为逆时偏移中的源端波场做正向传播,原始地震记录作为检波端波场做反向传播,方可获得具有自由表面多次波成像贡献的结果。数值试验结果表明,尽管一次反射波与自由表面多次波联合逆时偏移可以提供更宽的地下照明成像,但是,随着自由表面多次波能量的增强,偏移假象也随之增强;当自由表面多次波能量减弱时,尽管偏移假象相应减弱,但是自由表面多次波对宽角照明成像贡献也随之减弱。因此,一次反射波与自由表面多次波联合偏移成像需要更深入研究。

Under the condition of reverse time migration and cross correlation imaging, simultaneous migration images of primary and free surface multiples can provide wider underground illumination to make up for the insufficient coverage of the reflections, Therefore, it is not necessary to predict and separate multiples. However, migration artifacts may also be introduced during the process of joint imaging. In this paper, we firstly analyzed the simultaneous migration imaging conditions. Imaging with multiples information needs to use the source wavelet and reverse phase of seismic records as the source side wave field in the reverse-time migration and forward propagate, and the original seismic record as detection side wave field and back propagate, will obtain relative fidelity amplitude imaging results. The results of numerical experiments show that, although the simultaneous reverse time migration imaging of primary and free surface multiples based on cross-correlation imaging condition can provide wider underground illumination, the migration artifacts is also enhanced with the increase in the energy of free surface multiples. When the energy of multiples becomes weak, the intensity of wide-angle illumination by free surface multiples is also weakened, and therefore the simultaneous migration imaging of primary and free surface multiples needs to be further studied.