南苏丹境内裂谷盆地源上构造-岩性油藏成藏主控因素与成藏模式

Main controlling factors and hydrocarbon accumulation models of structurallithologic reservoirs above source kitchen in rift basins in South Sudan

以钻井、测井及三维地震资料等为基础,通过岩心分析、连井对比、油气运聚模拟、地震反演及多信息叠合等方法,从油源条件、储-盖组合和输导体系3个方面对南苏丹境内Melut和Muglad 2个裂谷盆地源上构造-岩性油藏成藏的主控因素进行了分析,并探讨了成藏模式。研究结果表明:①Melut和Muglad盆地均发育早白垩世第Ⅰ裂陷期优质烃源岩,厚度大、面积广、有机质类型好、成熟度适中,具有良好的油源条件;Melut盆地古近系Yabus组、新近系Jimidi组和Muglad盆地白垩系Aradeiba组发育三角洲相和河流相沉积,河道和水下分流河道微相砂体的含砂率、砂岩厚度均适中,且不同层序内河道的河型存在垂向演化,发育泛滥平原和水下分流间湾微相局部封隔带,形成多套源上砂泥互层储-盖组合,为形成规模构造-岩性圈闭提供了条件;边界控盆断裂与盆缘斜坡区控凹断裂是沟通主力烃源岩与源上目的层的主要油气垂向运移通道,源上层段发育的多期不整合面和富砂地层形成了多个侧向优势运移路径(输导脊),油源断裂与输导脊耦合控制Melut和Muglad盆地源上构造-岩性油藏的有利区带。②Melut盆地Yabus组、Jimidi组以及Muglad盆地Aradeiba组具备形成源上规模构造-岩性油藏的石油地质条件,成藏模式可分为“断裂垂向运移型”、“断裂垂向运移-不整合面侧向输导型”和“断裂垂向运移-连通砂体侧向输导型”3种。

Based on drilling,logging and 3D seismic data,core analysis,well correlation,oil and gas migration and accumulation simulation,seismic inversion and multi-information superposition methods were used to analyze the main controlling factors of structural-lithologic reservoirs above source kitchen in Melut and Muglad rift basins in South Sudan from three aspects:oil source conditions,reservoir and cap-rock assemblage and migration systems,and hydrocarbon accumulation models were discussed.The results show that:(1)The Melut and Muglad basins both developed high-quality source rocks in the I stage rifting period of the Early Cretaceous with large thickness,wide area,good organic matter type and moderate maturity,providing good oil source conditions.The Paleogene Yabus Formation and Neogene Jimidi Formation in Melut Basin,and Cretaceous Aradeiba Formation in Muglad Basin developed delta facies and fluvial deposits,and the microfacies sand bodies of river channels and underwater distributary channels had moderate sand content and sandstone thickness,and sealing zones in floodplains and underwater distributary bays are locally developed.The sand-mud interlayer reservoir and cap assemblage formed on multiple sources,and the reservoir and cap-rock assemblage and its vertical sedimentary evolution controlled the formation of large-scale structural-lithologic traps.The boundary-controlled basin faults and the depression-controlling faults in the slope area of the basin margin were the main vertical migration channels of oil and gas connecting the main source rock and the target layer above source kitchen.The multi-stage unconformities and sand-rich strata above source kitchen formed multiple lateral dominant migration paths(transport ridges).The coupling of the source faults and transport ridges controlled the favorable zones of the structural-lithologic reservoirs above the source kitchen in Melut and Muglad basins.(2)The Yabus Formation,Jimidi Formation in Melut Basin and Aradeiba Formation in Muglad Basin have the petroleum geological conditions for the formation of scale structural-lithologic reservoirs above source kitchen,and the accumula-tion models are vertical migration of fault,vertical migration of fault and lateral migration of unconformity plane,and vertical migration of fault and lateral migration of connected sandbodies.