叠前时间偏移技术在复杂地区三维资料处理中的应

在四川东部复杂地区，地表起伏大，地震地质条件复杂多变，表层速度变化剧烈；地腹构造褶皱强烈，逆冲断层发育，地震波传播速度纵横向变化大。为了得到好的成像效果，在作好静校正处理的基础上还要选择合适的偏移方法。折射层析静校正通过迭代求解，获得表层速度模型，在此基础上实现静校正量的计算，它将首波方法的稳定性和回折波方法的灵活性结合起来，较好地解决了复杂地区静校正问题；叠前时间偏移是复杂构造成像最有效的方法之一，能适应纵横向速度变化较大的情况，适用于大倾角的偏移成像。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；偏移的孔径过大，会降低低信噪比资料的偏移质量，在实际使用中应根据倾角来确定孔径。叠前偏移对偏移速度较敏感，较小的速度误差都可能影响偏移成像效果，在实际使用中通过迭代确定最佳偏移速度。文章对多个复杂地区的三维资料进行了叠前时间偏移处理，获得了归位精度高、质量好、断层断点清楚的成像剖面，为完成地质任务提供了较好的资料。

Application of Pre-Stack Time Migration Technology in 3D Seismic Processing in Complex Area

In complicated areas with large surface relief in the eastern Sichuan Basin, the seismic geologic conditions are complex and varied and surface velocity change greatly, while the subsurface structures are strongly folded with well developed thrust faults, resulting in great lateral and vertical changes of seismic wave propagation velocity. In order to improve effects of imaging, suitable migration method should be selected in addition to static correction. Refraction chromatography static correction can generate a surface velocity model through iteration, based on which the amount of static correction can be calculated. It combines the stability of the first arrival method with flexibility of inflection wave method and can well solve the problem of static correction in complex areas. Pre-stack time migration is one of the most effective imaging methods of complicated structures. It can adapt to large vertical and lateral variations of velocity and can be used to image high dipping structures. Migration aperture and velocity are the major factors that influence the effects of migration imaging. If the migration aperture is too small, the migration profile may lose events of steep dip. On the contrary, if the migration aperture is too large, the migration quality of data with low signal-to-noise ratio may decrease. An optimal aperture should be determined according to dip in practice. Pre-stack migration is sensitive to migration velocity. Even a small error in velocity may influence the quality of migration imaging. An optimal migration velocity should be determined through iteration in practice. Pre-stack time migration processing of the real 3D seismic data in several complicated areas has obtained imaging profiles with high migration accuracy, high quality and clear break points of faults, which lay solid foundations for geological research.