薄砂体重叠带与小断层的地震多属性联合识别方法研究

Identifying small fault and overlap strip of thin sand body based on seismic multi-attribute analysis

中国东部油田普遍存在断裂复杂、砂泥岩互层严重以及河道砂体间错落重叠等地质特征。由于地震纵向分辨率的限制,因而无法可靠识别低序级小断层和砂体重叠带,这对于油田开发方案的部署与调整影响很大。针对这一难题,设计了一个包含不同断距的断层和不同叠置范围及落差的重叠河道砂体模型,正演结果表明:小于调谐厚度的砂体重叠带在地震剖面上会形成“伪断层”响应,即与小断层类似的地震同相轴的扭曲或错断。但通过地震多属性的综合分析,发现了地震振幅类属性和地震波形结构类属性对小断层与砂体重叠带有不同的响应特征,结合常规的均方根振幅属性和波形变异系数属性,建立了两条识别准则:①均方根振幅与波形变异系数同时为低值突变可以识别断层存在;②均方根振幅为低值突变而波形变异系数为高值突变则可以识别砂体重叠带。胜利探区W102断块S23储层的地震资料应用结果表明,小断层发育区和薄砂体重叠带的均方根振幅和波形变异系数属性的异常特征与这两条识别准则基本一致,可用于识别与区分薄互层砂岩储层中的小断层与砂体重叠带,为该探区开发方案的调整部署提供了参考依据。

Oil fields in eastern China generally have complex faults,serious interbedding of sand and mudstone,and staggered overlap between river sand bodies.Owing to the limitation of seismic vertical resolution,it is impossible to reliably identify whether there are low-order small faults or sand body overlapping zones,which have a significant impact on the deployment and adjustment of oil field development schemes.In view of this problem,a model containing small faults with different fault throws and sand bodies with different overlapping ranges and falls was designed.The forward modeling results showed that the sand body overlap zone with thickness less than the tuning thickness that form a“pseudo fault”response on the seismic profile,that is,the distortion or dislocation of seismic event axis was similar to small faults.However,through a comprehensive analysis of seismic multi-attributes,it was found that seismic amplitude and seismic waveform structure attributes have different response characteristics to the overlap of small faults and sand bodies.Combined with the conventional root-mean-square(RMS),amplitude attribute,and waveform variation coefficient(WVC)attribute,two identification criteria were established.①When both the RMS amplitude and WVC attribute suddenly change to low values,the existence of faults can be recognized.②If the RMS amplitude is a low-value mutation and the WVC attribute is a high-value mutation,the overlapping zone of the sand body can be identified.These criteria were applied to the seismic data of the S23 reservoir in the W102 fault block of the Shengli exploration area.The results showed that the abnormal characteristics of the RMS amplitude and WVC attributes of the small fault development area and thin sand body overlap zone are consistent with these two identification criteria.Two thin sand body overlap zones in the north were identified,and they provide a reference basis for the adjustment and deployment of development schemes in this area.