珠江口盆地珠一坳陷断层阴影带成像技术与实践

断层圈闭是珠江口盆地珠一坳陷油气勘探的重要圈闭类型之一,断层阴影带的构造精确成像是该类型圈闭评价面临的最大挑战。勘探实践中形成了3种有效技术:①叠前深度偏移(PSDM)技术,引入断控+层位约束层析速度建模,可提升断层附近构造成像质量;②采集方向与断层平行或者夹角较小时,PSDM效果不够理想,采用基于正演模拟的断层阴影带构造成图方法,初步获得断层阴影带相对合理的构造形态,约束层析速度建模,可进一步改善PSDM成像效果;③重点靶区进行二次三维采集,形成以双方位联合层析速度反演和各向异性PSDM为核心的双方位融合处理技术,与单方位数据相比,双方位数据不仅信噪比大幅提高,而且有效消除了断层阴影带构造畸变。实际应用结果表明,断控+层位约束PSDM能有效改善断层阴影带成像;基于正演模拟的构造成图方法可以为PSDM速度建模提供更好的构造约束;垂直断层采集的地震资料有利于断层阴影带成像;多方位采集和融合处理是解决断层阴影带成像难题的最理想方案。

Fault traps are among the most important exploration targets in the Zhu I depression of the Pearl River Mouth Basin.Improving fault shadow imaging has become the main challenge in the evaluation of this type of trap.Three technological approaches have been developed during the exploration practice,namely fault-and-horizon constrained PSDM imaging,structural mapping,and repeated three-dimensional (3D) acquisition.With PSDM technology,the accuracy of fault shadow imaging has improved by employing the fault-and horizon-constrained tomographic inversion velocity.However,if the direction of seismic acquisition is parallel to the fault or the angle between them is small,the PSDM imaging in a fault shadow is usually not ideal.In such case,the structural mapping method,which is guided by seismic forward modeling,was employed to obtain an initial,relatively reasonable structure in the fault shadow.This provided a reasonably constrained structural trend for velocity modeling.As a result,the PSDM imaging quality was improved.In favorable areas,the 3D seismic acquisition was repeated,with optimized acquisition parameters (such as the acquisition direction).Then,dual-azimuth seismic processing centered on dual-azimuth joint tomographic velocity inversion and anisotropic PSDM was performed.The resulting dual-azimuth data provided a much higher signal-to-noise ratio as well as clearer illumination in the fault shadow zone compared to the individual data.An application of these methods showed that the fault-and-horizon constrained PSDM technology was effective in fault shadow imaging.The forward modeling-guided structural mapping method can provide better structural constraints for PSDM velocity modeling and further improve the imaging quality.Thus,seismic data acquired vertical to the fault strike are more suitable for fault shadow imaging.It is speculated that multi-azimuth technology will become the ideal solution to achieve fault shadow imaging in the future.

基金项目：“十三五”国家科技重大专项(2016ZX05024-004-006)资助。