叠前时间偏移是复杂构造成像有效的偏移方法之一,它能适应纵横向速度变化较大、倾角较大的偏移成像.影响偏移成像效果的主要因素是偏移孔径和偏移速度.偏移孔径过小,偏移剖面将损失陡倾角的同相轴；偏移孔径过大,会降低资料的偏移质量.虽然偏移孔径同野外采集孔径是完全不同的概念,但偏移孔径是受采集孔径约束的,采集孔径不够时,给再大的偏移孔径也不能使不同目的层的高角度数据很好地成像,因此合理设计野外采集孔径是决定最终成像质量的关键.对于一个工区的最深目的层而言,偏移孔径对采集的最大炮检距有很强的依赖性,偏移孔径只需略大于采集的最大炮检距的2倍即可,如果采集孔径不能满足目的层的需求,室内处理时给再大的偏移孔径也不会提高目的层高角度资料的成像质量.

Prestack time migration is one of effective migration method for a complex structure imaging,which can adapt to the imaging of steep dip angle and the large changes in vertical and horizontal velocity. The offset aperture and migration velocity are critical to imaging. If migration aperture is over small, the offset profile will loss the common phase axis of steep dip. If migration aperture is over big, it will reduce the quality of migration data. Though the concept of migration aperture is completely different from that of field acquisition aperture,the migration aperture is constrained by the acquisition aperture. If acquisition aperture is not enough many, it will not precisely image the data of steep-dip and middle-deep formation. So the suitable design of field acquisition aperture is crucial to the final imaging quality. To the deepest target area of a survey, the migration aperture comparatively depends on the acquisition aperture and the migration aperture only needs a slightly larger twice of the largest offset. If acquisition aperture can not satisfy the imaging demand of the target area, no matter how long the migration aperture in data processing is added to, the imaging quality of steep dip angle in target area can not be improved also.