玛湖凹陷及周缘白碱滩组勘探突破与新认识

Exploration Breakthrough and New Insights of Baijiantan Formation in Mahu Sag and Its Periphery

为明确玛湖凹陷白碱滩组砂体分布规律和油气成藏模式,评价其油气勘探前景,综合钻井、测井、地震、分析化验等资料,系统梳理白碱滩组二段沉积规律和成藏特征。白碱滩组二段为辫状河三角洲—滩坝—浊积扇沉积序列,发育水下分流河道砂、滩坝砂和浊积砂3种不同类型的砂体,辫状河三角洲前缘亚相以河道砂为主,滨—浅湖发育滩坝砂,半深湖—深湖受坡折带控制发育多个浊积扇体,浊积砂呈朵叶状分布,建立了水下分流河道—滩坝—浊积扇的沉积控砂模式。研究区发育9大走滑断裂体系,其中,走滑断裂直通型、走滑断裂伴生型和走滑断裂接力型3种断裂组合能够有效沟通二叠系风城组烃源岩,作为油气垂向高效运移通道,白碱滩组二段整体具有走滑断裂通源、断裂砂体配置控藏和优质储集层富集的成藏模式。

In order to clarify sandbody distribution patterns and hydrocarbon accumulation model of the Baijiantan formation in the Mahu sag,Junggar basin,and evaluate its hydrocarbon exploration prospects,the drilling,logging,seismic and experimental data were compre⁃hensively analyzed to understand the sedimentary patterns and hydrocarbon accumulation characteristics of the second member of the Baiji⁃antan formation(Bai⁃2 member).It is found that the Bai⁃2 member represents a braided⁃river delta-beach bar-turbidite fan sedimentary se⁃quence,with three types of sandbodies of underwater distributary channel,beach bar and turbidite fan.Channel sandbodies are dominant in braided⁃river delta front;beach bar sandbodies are developed in shore⁃shallow lake;controlled by slope breaks,multiple turbidite fans are developed in deep lake to semi⁃deep lake,with turbidite fan sandbodies distributed in a lobate pattern.Thus,a sedimentary pattern of un⁃derwater distributary channel-beach bar-turbidite fan was established.Nine major strike⁃slip fault systems are found in the study area.Among them,three types of fault combinations such as through⁃type,associated⁃type,and relay⁃type strike⁃slip faults effectively connect the Permian Fengcheng formation source rocks and serve as efficient vertical pathways for hydrocarbon migration.The Bai⁃2 member fol⁃lows a hydrocarbon accumulation model characterized by strike⁃slip faults connecting source rocks,fault⁃sandbody configuration control⁃ling reservoir,and hydrocarbon enrichment in high⁃quality reservoirs.