海上三维双方位融合处理技术在番禺4洼的应用

Application of offshore 3D dual-azimuth seismic data processing to the Panyu 4 Sag

番禺4洼新近系NWW-SEE向正断层非常发育,这些断层上升盘的构造圈闭是重要的勘探目标。但由于一次三维地震资料采集方向与断层平行,断层附近阴影现象非常严重,表现为信噪比低、同相轴不合理的“下拉”和扭曲畸变的“假象”,严重影响断层上升盘的精细构造落实。为此,实施了垂直于断层方向的二次三维地震采集,使得断层阴影带成像比一次三维有较大改善。为了更好地解决断层阴影带成像难题,针对方位各向异性,对2次采集的三维资料进行了以双方位各向异性叠前深度偏移(PSDM)为核心的双方位融合处理。2个方位各自处理成果和双方位融合处理结果对比表明:对于断层阴影带成像,垂直断层方向采集的三维明显优于平行断层方向采集的三维;而结合2次采集的双方位融合处理资料效果最好:既能有效的消除断层阴影带成像畸变,又能提高信噪比。经研究区油田评价井在断层阴影带的钻探结果证实了双方位融合处理结果的可靠性,同时,可为类似地区解决断层阴影带成像难题提供采集设计和处理技术等方面的借鉴。

The study area, Panyu 4 Sag, occurs in the northern part of the Pearl River Mouth Basin where Neogene NWW-strike normal faults are well developed. The traps on the upside of those faults are important targets for hydrocarbon exploration. However, the first round of 3D seismic data of this area, which is parallel to the direction of fault strike, provides poor images in fault shadow zones, with low signal-to-noise ratio, abnormal event dropping down and strong structural distortion. Thus traps on the upside of normal faults always bear structural uncertainties in data interpretation. For this reason, a second round of 3D seismic is performed vertical to fault strike and fault shadow imaging is improved compared to the first round of 3D seismic. In order to further improve the fault shadow imaging, the dual-azimuth processing considering azimuthally anisotropic is employed using both of the 3D seismic datasets. The core of the dual-azimuth processing is the dual-azimuth anisotropic PSDM. By comparison of the dual-azimuth anisotropic PSDM results and the PSDM results using either of the single azimuth, it is found that the seismic data which is acquired vertical to the fault strike is more suitable for fault shadow imaging. What’s more, the dual-azimuth data shows the best illumination in fault shadow, as well as the highest signal-to-noise ratio. The reliability of the dual-azimuth data is demonstrated by the drilling results of the evaluation wells in the fault shadow zone. At the same time, some references on seismic acquisition design and data processing flow can be provided for solving the imaging problem of fault shadow zone in similar areas.