冀中坳陷奥陶系潜山油气藏形成条件与成藏模式

Formation conditions and reservoir forming models of Ordovician buried hill reservoirs in Jizhong Depression

冀中坳陷潜山是增储上产的重要领域,奥陶系潜山由于储层非均质性强、控藏因素复杂,因此一直制约着油气勘探的新发现。基于大量岩心、薄片、测井、地震及地球化学数据和地质分析的基础上,对其成藏条件及成藏模式进行了系统分析,指导杨税务潜山、文安斜坡潜山勘探取得重要突破。研究表明:冀中坳陷发育古近系沙三段和沙四段以及上古生界石炭—二叠系3套烃源岩,为潜山油气藏的形成提供了充足的物质基础;明确了碳酸盐岩“云化-岩溶-断裂”三主因叠合控储机理,建立了岩溶孔洞型、断裂孔缝型和云岩孔隙型3种储层模式,拓展了勘探空间;受印支期、燕山期、喜山期多期构造作用叠加控制,形成了先隆后凹型和先凹后隆型两种成因潜山圈闭类型。通过奥陶系潜山成藏要素分析,总结出3种潜山油气成藏模式:低位构造-岩性复合准层状潜山成藏模式、中位古储古堵块状潜山成藏模式和高位古储新堵块状潜山成藏模式。综合评价,目前冀中坳陷北部低位构造-岩性复合准层状潜山成藏条件最为有利,泗村店潜山和新镇潜山是下一步勘探的有利方向。

Buried hills in the Jizhong Depression are important exploration targets for petroleum production/reserve enhancement.Ordovician buried hill,however,hinders petroleum discovery due to its strong reservoir heterogeneity and complex reservoir-control factors.Here,based on abundance of core,thin section,logging,seismic and geochemical data,and on the basis of geological analysis,the reservoir-forming conditions/modes of the Yangshuiwu and Wen an-slope buried hills are systematically analyzed to guide explorations for major breakthroughs.The study shows that three sets of source rocks of the 3 rd and 4 th members of the Paleogene Shahejie Formation and upper Paleozoic Carboniferous-Permian are developed in the Jizhong Depression,providing sufficient material basis for the formation of buried hill oil/gas reservoir.The reservoir-control mechanism including three main factors—carbonate dolomitization/karst/fault—is ascertained,and three reservoir models of karst-pore type,fault-pore fracture type and dolomite-pore type—are established,expanding the exploration space.Controlled by multi-stage tectonism in Indosinian,Yanshanian and Himalayan periods,two types of buried hills were formed:one was formed from depressed strata after uplift and the other from uplifted strata after depression.Based on the analysis of reservoir-forming factors of Ordovician buried hills,three models of buried hills are concluded:deep structural and stratigraphic buried hills with layered reservoirs,median buried hills trapped by Mesozoic and Upper Paleozoic mudstones,and shallow buried hills sealed by Paleogene mudstones.In conclusion,the deep structural and stratigraphic buried hills with layered reservoirs in northern Jizhong Depression have the most favorable reservoir-forming conditions,and the Sicundian and Xinzhen buried hills are the favorable exploration targets.