塔里木盆地古城地区奥陶系鹰山组白云岩特征及孔隙成因  

Characteristics and pore genesis of dolomite in Ordovician Yingshan Formation in Gucheng area, Tarim Basin

作　　者：王珊[1] 曹颖辉[1] 杜德道[1] 张亚金[2] 刘策[1] WANG Shan;CAO YingHui;DU DeDao;ZHANG YaJin;LIU Ce(PetroChina Research Institute of Petroleum Exploration&Development,Beijing 100083,China;PetroChina DaQing Oilfield Company,Daqing,Heilongjiang 163712,China)

机构地区：[1]中国石油勘探开发研究院,北京100083 [2]大庆油田有限责任公司勘探开发研究院,大庆163712

出　　处：《岩石学报》2020年第11期3477-3492,共16页Acta Petrologica Sinica

基　　金：中国石油天然气股份有限公司十三·五专项项目(2019B-04);中国石油重大科技专项项目(2016E-0204)联合资助。

摘　　要：奥陶系鹰山组白云岩是塔里木盆地的重点勘探领域,优质白云岩储层是制约其勘探的关键难题。本文在前人研究基础之上,结合多口井岩心薄片观察、同位素、微量元素等地球化学分析,对古城地区奥陶系鹰山组白云岩成因、孔隙成因以及储层主控因素进行了深入研究,认为古城地区鹰山组发育粉晶、粉细晶、细晶、细中晶、中晶、粗晶6种白云岩。粉晶和粉细晶白云岩碳、锶同位素分布范围均与同时期灰岩一致;氧同位素值与同时期白云石一致或偏正;锶元素含量相对较高;稀土元素与同时期灰岩分配模式相同。以上特征表明该类白云岩形成于蒸发海水环境,为准同生海源成因。细晶、细中晶、中晶及粗晶白云岩碳同位素值与同期灰岩总体一致;氧同位素值与正常海相白云石一致或偏负;锶同位素值与灰岩背景值一致或偏高;锶元素含量相对较低;大部分样品Eu正异常。以上特征揭示该类白云岩主要为中浅埋藏成因,并且叠加了早期淡水溶蚀及晚期埋藏-热液改造。孔隙成因分析表明高能缓坡滩是孔隙形成的物质基础、准同生暴露溶蚀是孔隙形成的关键、早期白云石化有利于孔隙的继承和保存,构造破裂和埋藏-热液溶蚀对孔隙起到有利的改造作用。白云岩规模优质储层受控于云化滩和断裂热液溶蚀改造,二者叠合之处为规模优质储层发育区。这一认识为研究区下一步勘探部署提供了重要依据。The dolomite of Ordovician Yingshan Formation is a significant exploration field in Tarim Basin. High-quality dolomite reservoir is the key factor restricting exploration. On the basis of previous studies,combined with core,thin section observation,isotope analysis and trace element analysis,this paper makes a deep study on the dolomitization genesis,pore genesis and controlling factors of dolomite reservoir in Yingshan Formation. The study shows that micrite dolomite,micrite-to fine-grained dolomite,finegrained dolomite,fine-to medium-grained dolomite,medium-grained dolomite and coarse-grained dolomite are the 6 dolomite types in research area. Geochemical analysis shows that the distribution range of carbon and strontium isotopes of the micrite dolomite and micrite-to fine-grained dolomite are consistent with that of the limestone in the same period;the oxygen isotopic value is consistent with that of dolomite in the same period;the content of strontium element is relatively high;and the distribution pattern of rare earth elements is the same with that of the limestone in the same period, which indicates the dolomitization took place in penecontemporaneous phase. The carbon isotope values of fine-grained dolomite,fine-to medium-grained dolomite,medium-grained dolomite and coarse-grained dolomite are consistent with limestone in the same period,and the oxygen isotope are consistent or negative compared with normal marine dolomites;strontium isotope values are consistent with or higher than those of limestone background values;the content of strontium element is relatively low;most of the samples have positive Eu anomalies,The above characteristics reveal that the dolomitization mainly took place in shallow-medium buried phase,and partially influenced by paracontemporaneous exposure dissolution and hydrothermal. The study of pore genesis shows that the high-energy grainstone shoal is the material basis of pore formation,paracontemporaneous exposure dissolution is the key factor of pore formation,early dolomitizat

关 键 词：白云岩 孔隙成因 奥陶系鹰山组 塔里木盆地 古城地区 

分 类 号：P588.245[天文地球—岩石学]