张扭性盆地隐性断裂带识别、演化及控藏作用——以苏北盆地金湖凹陷为例

隐性断裂带是由区域或局部应力场或基底断裂活动影响下, 在凹陷沉积盖层中产生的断裂趋势带。重磁、三维地震资料处理解释成果证实苏北盆地金湖凹陷存在北东、北西两组基底断裂。部分北东向的基底断裂活动强烈, 控制了凹陷形成和演化; 北西向和部分北东向的基底断裂活动性较弱, 沉积盖层中形成了隐性断裂带。它们表现为成带分布的雁列式小断层、断断续续沿固定方向分布的小断层、一系列沉积扇体或油气圈闭成带成串分布等线状构造。随机测线的剖面上表现为地震同相轴没有明显错断或呈现杂乱反射。除上述两组隐性断裂带, 区域右行应力场在凹陷内部产生的东西方向的挤压应力分量也形成了断续状、串状的南北向隐性断裂带。研究表明, 隐性断裂带由"隐性"逐渐向"显性"过渡。经历了早期弱雁列式隐性期、早中期强雁列式隐性期、中期断续状隐-显期、中后期串状显-隐期4个隐性阶段, 最终演化为"显性"张扭性走滑断裂。沉积盖层中形成的这些隐性断裂带控制了储集砂体分布、改善了储层物性、使隐性圈闭成带成串分布, 是油气聚集成藏的有利区带。

Evolution of subtle fault zone and its control function of reservoirs forming in Jinhu sag

Subtle fault zone is a weak deformation trend zone which is produced in sedimentary basin's cover. It is formed under the influence of regional or local stress field or basement fault's activity. It is often ignored, because it is obscuring, concealing, and difficult to identify. Gravity and magnetic data with regional geological data have verified that the basement existence NE-trending faults and NW-trending faults. Part of the NE-trending basement fault's activity is strong, controlling the formation and evolution of depression, such as Yangcun and Shigang faults; The NW-trending and part of the NE-trending basement faults' activity are weak, having little effect on the sedimentary cover's deformation, only forming some weak deformation zones in the sedimentary cover, sometimes appears as en-echelon faults distributed in belts, small faults distributed discontinuously along a fixed direction, a series of oil traps or sedimentary facies distributed in belts, small fold or deep narrow half-graben. They are linear structures. Seismic profile showed the major section steep cut into the basement or the flower-form structure without the root. There are no leap in the shallow layer seismic event or showing disorder reflection. They are discontinuous and concealment, so called "subtle" fault zones. Except the two type on the above, the NW-trending compressive stress component generated by the regional dextral strike stress field in the depression formed NS-trending subtle fault zones. They are distributed in discontinuously or string style. The results show that the subtle fault zones could be divided into early weak en echelon faults stage, early-middle strong en echelon faults stage, middle discontinuously faults stage, middle-late string style faults stage and late extention torsional strike-slip faults stage. The subtle fault zones control the distribution of the sandbody, improve the reservoir physical property, make the subtle reservoir distributed in zones, it is favorable zones for hydrocarbon accumulation. Make further discussion of the evolution and its control function of reservoirs forming has important significance for petroleum exploration in the sedimentary basin.