塔里木盆地奥陶系鹰山组多类型白云岩储层成因机制

Genetic mechanism of multi-type dolomite reservoirs in Ordovician Yingshan Formation,Tarim Basin

塔里木盆地奥陶系鹰山组是油气勘探重要领域之一,发育多类型白云岩储层,其成因机制是较为关注的问题之一。基于构造-沉积背景分析、薄片鉴定、阴极发光与扫描电镜等分析手段,结合原位微区碳氧同位素、全岩碳-氧-锶同位素和流体包裹体等数据,分别解剖了浅埋藏型、岩溶型与热液改造型白云岩储层的显微岩石学与地球化学特征。浅埋藏白云石化相关储层的白云石自形程度好,不同产状白云石具有较一致的碳氧同位素组成,反应了相似的白云石化流体来源特点。岩溶型白云岩储层表现为去白云石化作用与大气淡水成因方解石的胶结,具有贫18 O和富放射性87 Sr特征。热液改造型白云岩储层通常以萤石和石英等热液矿物为典型标志。热液流体通常具有高温高盐度特点,形成储集空间的过程中相关白云石与方解石胶结物以贫18 O和Eu正异常为特征。白云岩储层的多成因特点决定其发育分布受岩相、局部构造位置和流体性质等多因素的控制。

The Ordovician Yingshan Formation is one of the most important targets of petroleum exploration in the Tarim Basin.The genetic mechanism of well-developed dolomite reservoirs of multiple types has always been a focus of study here.The micropetrologic and geochemical characteristics of various dolomite reservoirs,including shallow buried,karstified and hydrothermal modification types,are revealed through analyses of tectonic-sedimentary setting,thin section observation and scanning electron microscopy,combined with in-situ carbon-oxygen isotopes,whole-rock carbon-oxygen-strontium isotopes,and fluid inclusion data.The dolomite reservoir of shallow-buried type is characterized by obvious euhedral crystals,and the consistent carbon and oxygen isotope compositions of mineral dolomite with different occurrences,reflecting the similar source of dolomitization fluids.The dolomite reservoir of karstified type is characterized by dedolomitization,calcite cementation of meteoric water origin,and negativeδ18 O values and rich radiogenic 87 Sr.The dolomite reservoir of hydrothermal modification type is typically characterized by such hydrothermal minerals as fluorite and quartz.Its hydrothermal fluids are typically high in temperature and salinity,and the dolomite and calcite cements are characterized by negative 18 O and Eu positive anomaly in forming the reservoir space.The multiple origins of dolomite reservoirs determine that their development and distribution are controlled by many factors including lithofacies,local structural locations,and fluid properties.