两步法地震深度成像技术及其应用效果

在地震资料信噪比较高的地区,采用叠前深度偏移技术获得的深度剖面,可较好地反映实际构造形态。但在地震资料信噪比低的山地复杂构造区,叠前深度偏移处理周期长,成像普遍较差,难以满足构造地质研究和油气勘探发展的需求。两步法地震深度成像是一种快速准确的成像方法。第一步在时间域里归位,采用叠后时间偏移或叠前时间偏移,对叠加剖面上的横向畸变现象(回转波、绕射波、断面波及倾斜反射波)进行偏移。第二步在深度域里归位,在偏移时间剖面上,建立有井约束层速度模型,通过变速时深转换,实现纵向归位,纵向上消除受速度"上拉效应"形成的假背斜和假高点,最终获得能真实反映地下构造形态的深度剖面。该项技术已在复杂油气田勘探开发中得到广泛应用,并取得良好的应用效果。

Two-Step Seismic Depth Imaging Technology and Its Application Result

Adoption ofpre-stack depth migration technology for depth cross-section in a region where the seismic data S/N ratio is high can satisfactorily reflects the pattern of actual structure. However, in a mountainous complicated structural region where the seismic S/N ratio is low, pre-stack depth migration processing is difficult to meet the requirements for geological study of structure and development of oil and gas exploration because of a long period and a poor imaging quality. Two-step seismic depth imaging is a rapid and precise imaging method. The first step is migration in time domain, adopting post-stack time migration or pre-stack time migration to migrate the lateral distortion phenomena on the stack cross-section （such as bow-tie, diffraction, fault plane reflection and dipping reflection）. The second step is migration in depth domain, vertically eliminating false anticline or false structure high caused by velocity ＂pull-up effect＂ and finally acquiring the really-reflected depth profile of underground structure. This technology has been extensively used in exploration and development of complicated oil and gas fields with good application results achieved.