摘要
歧口主凹新部署的HT1井在东营组三亚段(东三段)钻遇一套重力流砂体并获工业油流,取得了主凹区的勘探突破,但是目前对其物源方向和空间展布特征尚不明确,制约了下步勘探工作。基于地震和测录井资料,利用碎屑锆石LA-ICP-MS U-Pb定年方法对歧口主凹区东三段砂岩开展了源−渠−汇约束下的沉积体系研究工作。碎屑锆石U-Pb定年结果表明,歧口主凹东三段砂岩碎屑锆石年龄主要集中在160~100,300~240,2000~1680,2600~2300 Ma 4个年龄区间内,其中160~100 Ma区间年龄峰值明显。盆外物源区沧县隆起FU1X1井东三段砂岩碎屑锆石年龄在二叠纪(300~240 Ma)具有明显峰值。北部燕山造山带发育有从太古宙到中生代的岩浆岩,中生代岩浆作用强烈,160~100 Ma区间的年龄峰值特征明显。HT1井东三段砂岩碎屑锆石年龄特征与燕山造山带年龄峰值特征具有较高一致性,表明北部燕山造山带为其物源区。结合前人轻重矿物研究成果和东三段沉积时期歧口主凹区北高南低的古地貌特征,构建了歧口主凹区东三段砂岩“远源供砂、沟槽输砂、深凹聚砂”的沉积模式。研究成果为后续主凹区井位部署提供了依据。
[Objective]The Qikou Sag,a significant hydrocarbon-bearing sub-basin within the Bohai Bay Basin of eastern China,has recently witnessed a critical exploration breakthrough.Well HT1,drilled in the main trough,encountered a sandstone reservoir within the Third Member of the Dongying Formation(Ed3)and achieved commercial oil flow.However,the precise provenance and spatial distribution of this Ed3 sandstone remain enigmatic.Identifying the sediment source is fundamental to constructing a reliable"source-to-sink"system,which is crucial for predicting the distribution of high-quality reservoirs.This study aims to definitively determine the provenance of the Ed3 sandstone through detrital zircon U-Pb geochronology and establish a robust sedimentary model to guide exploration.[Methods]To address the provenance question,this study employed laser ablationinductively coupled plasma-mass spectrometry(LA-ICP-MS)U-Pb dating on detrital zircons extracted from the Ed3 sandstone.Zircon is an ideal mineral for provenance analysis due to its high physical and chemical stability,allowing it to survive multiple cycles of erosion and transport while preserving its primary crystallization age.Thus,the age spectrum of detrital zircons in a sedimentary rock serves as a unique fingerprint that can be compared to the age signatures of potential source areas,enabling a direct link between the sediment and its origin.[Results]The UPb dating results from the Ed3 sandstone revealed a characteristic age distribution pattern.The detrital zircon ages cluster into four primary intervals:2600−2300 Ma(Neoarchean to Paleoproterozoic),1680−2000 Ma(Paleoproterozoic),300−240 Ma(Permian),and a remarkably dominant peak between 160−100 Ma(Jurassic to Cretaceous).The overwhelming abundance of zircons in the 160−100 Ma range immediately pointed towards a significant contribution from a source region with intense Mesozoic magmatic activity.The zircon age signature of the Cangxian uplift was examined.Its age spectrum is characterized by a strong peak at 300−240 Ma and a relative lack of Mesozoic zircons,presenting a clear mismatch with the Ed3 sandstone signature and effectively ruling it out as the primary source.In contrast,the Yanshan orogenic belt to the north is a complex tectonic zone with a prolonged magmatic history spanning from the Archean to the Mesozoic.Critically,it is renowned for widespread Jurassic-Cretaceous(Yanshanian)magmatism,with a pronounced age peak precisely between 160 and 100 Ma.The striking similarity between the Ed3 zircon age pattern and the magmatic record of the Yanshan belt provides compelling evidence that the latter served as the principal provenance for the sandstone.Previous studies indicate that the Yanshan orogenic belt experienced significant Cenozoic uplift,coeval with the deposition of the Ed3,creating a well-defined mountain-basin system.Several major paleo-rivers,such as the ancient Yongding River,ancient Chaobai River,and ancient Luan River,are interpreted to have acted as efficient sediment conduits.These rivers eroded the Mesozoic granitic rocks of the Yanshan belt and transported the detritus southward over long distances into the Qikou Sag.[Conclusions]This study successfully resolves the provenance of the Ed3 sandstone in the main trough of the Qikou Sag.Detrital zircon U-Pb geochronology unequivocally identifies the northern Yanshan orogenic belt as the primary source,excluding the nearby Cangxian uplift.The construction of the"remote source,channelized transport,deep-trough deposition"model has profound implications for exploration.It validates the existence of high-quality sandstone reservoirs in the deep troughs formed by long-distance transport systems.Consequently,future exploration efforts should prioritize mapping the paleo-drainage pathways that funneled sediments from the Yanshan belt into the main trough of the Qikou Sag.This model significantly reduces exploration risk in the deep plays of the depression and provides a valuable analog for searching for similar subtle reservoirs in other continental rift basins worldwide.
作者
李长海
董晓伟
石倩茹
官全胜
张佼杨
朱华汇
张明振
董越崎
付东立
杨帆
LI Changhai;DONG Xiaowei;SHI Qianru;GUAN Quansheng;ZHANG Jiaoyang;ZHU Huahui;ZHANG Mingzhen;DONG Yueqi;FU Dongli;YANG Fan(PetroChina Dagang Oilfield Company,Tianjin 300280,China)
出处
《地质科技通报》
北大核心
2025年第5期65-81,共17页
Bulletin of Geological Science and Technology
基金
国家科技重大专项“渤海湾超级盆地油气富集规律与新领域勘探关键技术”(2024ZD1400100)
中国石油大港油田公司博士后项目“歧口凹陷断砂耦合形成机制与控藏规律研究”(博057)。
