苏北盆地浅层油气藏类型及分布特征

苏北盆地发育3种具有不同成藏主控因素的浅层油气藏,分别是阜二段中下部低熟高效烃源岩型、断裂垂向通道型及大型砂体侧向运移型浅层油气藏。浅层油气藏的分布极不均衡,盆地西侧的金湖、高邮凹陷浅埋藏油气藏最为发育,且类型齐全,规模也较大。这种分布特征与郯庐断裂带控制了盆地的构造、沉积演化,从而对该盆地浅层油气藏的成藏主控因素起重要控制作用密切相关。表现为郯庐断裂周缘断陷是阜二段中下部优质低熟高效烃源岩及阜二段底部、阜一段上部砂体发育区,形成大量与阜二段中下部低熟高效烃源岩相关的浅埋油气藏。郯庐断裂周缘发育继承性及早期型深断陷,具有较高的大地热流场,油气成熟早,有利于油气较长期通过断裂向上运移,且靠近郯庐断裂的区域断裂密度大、活动期次多,有利于形成断裂通道型的浅层次生油气藏。因此,郯庐断裂周围的金湖、高邮及溱潼凹陷浅层油气资源最丰富,浅层油气藏主要分布在控凹同生断裂带及内、外斜坡带的走滑花状断裂系。在苏北盆地,围绕上述3种类型浅层油气藏,按各区的浅层油气藏形成分布规律开展针对性勘探,还有较大的勘探潜力。

TYPES AND DISTRIBUTION CHARACTERISTICS OF SHALLOW RESERVOIRS IN THE NORTH JIANGSU BASIN

There are three types of shallow reservoirs controlled by different key factors for hydrocarbon accumulation in the North Jiangsu Basin,respectively controlled by low maturity and high efficiency oil source rock in the lower-middle part of the Fu2 Member,fault of vertical migration pathway,and large scale sandstone for lateral migration.Distribution of shallow reservoirs is featured with hyperdispersion in the North Jiangsu Basin.Shallow reservoirs are developed in the Jinhu Sag and Gaoyou Sag in western basin,with various types and large scales.This distribution feature is correlated to the Tanlu Fault Belt controlling the structure and deposit evolution of basin as well as the key factors for hydrocarbon accumulation.The evidence is that the periphery of Tanlu fault depressions is well-developed of low maturity and high efficiency oil source rock in the lower-middle part of the Fu2 Member,sandstone in the bottom part of the Fu2 Member and the upper part of the Fu1 Member,forming abundant shallow reservoirs.Periphery Tanlu fault depressions are inherited from early deep rift with high geothermal gradient,with earlier matured oil.Faults are polyformative and of high density in the area near the Tanlu Fault Belt,which helps to form secondary shallow reservoirs of fault-passway type.Consequently,there are a lot of shallow reservoirs in the Jinhu Sag,the Gaoyou Sag and the Qintong Sag around the Tanlu Fault Belt.Shallow reservoirs distributed over the growth fault zone and the strike-slip flower fault system in inner-outer slope.There is a great exploration potential in the North Jiangsu Basin,if we aim at the three types of shallow reservoirs,and focus on their forming and distribution rules in these areas.