OVT域五维地震属性在双鱼石地区栖霞组裂缝预测中的应用

Application of OVT-domain 5-dimensional seismic attributes in fracture prediction in the Qixia Formation of the Shuangyushi area

川西北双鱼石地区栖霞组超深层碳酸盐岩储层横向非均质性强、构造复杂、钻井多、井下天然气产量差别大。利用OVT域五维地震数据对该套储层开展了裂缝预测、含气性检测和实钻井验证分析。首先基于OVT域不同方位地震属性所存在的差异来检测碳酸盐岩储层裂缝、溶洞。其次是分方位属性分析,寻找含气地震响应特征更敏感的优势方位范围,该优势方位内更有利于含气性检测。两方面的研究工作在双鱼石区块栖霞组裂缝预测和含气性检测方面都取得了良好的应用效果,研究表明:双鱼石地区栖霞组裂缝发育程度较高,主要发育三种方向的裂缝,多数裂缝与断裂走向斜交;垂直断裂方向地震数据突出方位各向异性,有利于小断层识别;平行断裂方向地震数据可以较好规避断裂导致的各向异性,突出油气响应特征,更有利于油气检测。有针对性叠前、叠后含气性检测方法能有效地预测研究区栖霞组储层及含气性展布特征,天然气富集区主要分布在研究区的中部和东南部,并沿NE-SW向呈连片条带状展布。

The ultra deep carbonate reservoir of the Qixia Formation,Shuangyushi area,northwestern Sichuan features strong lateral heterogeneity,complex structure,many drilling wells and great disparity in downhole natural gas production.Using OVT-domain 5-dimensional seismic data,fracture prediction,gas-bearing property assessment and real drilling verification analysis are carried out for this set of reservoirs.The first task is to detect fractures and karst caves in the carbonate reservoirs based on the differences in OVT-domain seismic attributes between different directions.The second task involves analyzing azimuth attribute to find the dominant azimuth with seismic response more sensitive to gas-bearing formations thus more conducive to a positive detection outcome.Both tasks achieved good results in the Qixia Formation,Shuangyushi block in fracture prediction and gas-bearing property assessment.The extent of fracture development in the Qixia Formation,Shuangyushi area is relatively high,and fractures are mainly developed in three directions and oblique to the fault strike.Fault normal seismic data highlight the azimuthal anisotropy and can better detect small faults,while in the fault parallel direction fault-induced seismic anisotropy can be minimized for better oil and gas detection.Targeted pre-stack and post-stack gas detection methods can effectively predict the distribution characteristics of gas-bearing reservoirs of the Qixia Formation in the study area.According to the prediction the natural gas enrichment areas mainly distribute in the middle and southeastern parts of the study area,in contiguous strips along the NE-SW direction.