渤海湾盆地渤中凹陷油藏断裂特征及对成藏的控制作用

Characterization of fault system and its control on reservoirs in the Bozhong Sag,Bohai Bay Basin

渤中凹陷是环渤海湾盆地的沉积沉降中心,也是环渤海湾盆地重要的富油气凹陷之一。目前在凹陷周边所发现的油藏绝大部分是受断裂控制的构造或构造-岩性油气藏,这些断裂对油气藏的控制方式和影响程度,直接决定构造圈闭的评价结果和勘探部署方案。对渤中凹陷目前已发现的237个中浅层油气藏构造特征进行精细解剖,统计对比了断裂的级别、成因类型、断距、断层活动性、断层产状、组合样式、平面形态、遮挡类型、断层泥比率等指标与相应的油藏发育程度,发现在主断裂与次级断裂的合理配置的前提下,渤中凹陷中浅层有利于成藏的断裂特征为:走向NNE、近EW和NE,倾角66°~80°,断距20~150 m,断层活动速率在10~30 m/Ma,断层泥比率SGR大于0.3,断裂带泥质含量R_m大于0.35,组合样式为斜交式、雁列式、Y字形、似花状和阶梯状,并且断裂以反向遮挡为主。平面上在断裂相交处、凸形增压段更有利于油气聚集成藏。本质上说,断层封闭性是控制构造圈闭成藏的关键,断裂活动速率、规模和断裂类型是影响封闭性的根源。

The Bozhong Sag is not only the depocenter of the Bohai Bay Basin,but also an important oil/gas-bearing sag in the Bohai Bay Basin.The reservoirs surrounding the Bozhong Sag are mostly fault-controlled structural or structural-lithological reservoirs.The patterns and degrees that these faults control on petroleum reservoirs directly determine the evaluation of structural traps and exploration strategy.By detailed structural characterization of 237 petroleum reservoirs with shallow to medium depth in the Bozhong Sag,this paper statistically analyzed multiple parameters,e.g.,faulting classification,faulting mechanism,fault throw,faulting activity,fault strike/dip,combination styles,plain view geometry,screening types,SGR,etc.Our study suggested that,with proper assemblage of primary faults and minor faults,faulting characteristics contributing to petroleum accumulation includes：striking NNE or EW/NE,dip angle of 66°-80°,fault throw of 20-150 m,faulting rate of 10-30 m/Ma,SGR 〉 0.3,Rm 〉 0.35,multiple assemblage styles （e.g.,oblique crossing,en echelon,Y-shape,semi-flower and stepwise faults） and antithetic screening.In plain view,it is more favorable for hydrocarbon accumulation in positions where faults are intersecting and convex section.In general,fault sealing property is the key factor controlling hydrocarbon accumulation in structural traps.The fault sealing property is determined by faulting rate,scale and fault types.