准噶尔盆地西北缘北东段下二叠统风城组白云质岩岩石学和岩石地球化学特征  

Petrological and Geochemical Features of Dolomitic Rocks in the Lower Permian Fengcheng Formation in Wuerhe—Xiazijie Area,Junggar Basin

作　　者：朱世发[1,2] 朱筱敏[1,2] 刘英辉[1,2] 陈相亦[1,2] 王俊怀 王小军[3] 马爱钰 

机构地区：[1]中国石油大学(北京)油气资源与探测国家重点实验室,北京102249 [2]中国石油大学(北京)地球科学学院,北京102249 [3]中国石油新疆油田分公司勘探开发研究院,新疆克拉玛依834000

出　　处：《地质论评》2014年第5期1113-1122,共10页Geological Review

基　　金：国家油气重大专项(编号2011ZX05009-002-104);国家自然科学基金青年科学基金(编号41202107);教育部高等学校博士学科点专项科研基金(新教师类)(编号20120007120004);中国石油大学(北京)科研基金(编号KYJJ2012-01-20)资助项目的成果

摘　　要：白云质岩类是准噶尔盆地西北缘北东段乌尔禾—夏子街地区二叠系风城组最为重要的油气储层类型,已提交石油三级储量近亿吨。在前人研究基础上,本文采用岩石学和岩石地球化学相结合的分析手段,探讨这套特殊白云质岩的成因机制,为准噶尔盆地西北缘白云质岩致密油勘探、评价提供科学的地质依据。通过X衍射、阴极发光、扫描电镜观察及岩石薄片镜下鉴定认为,发生白云石化作用的母质为火山凝灰物质以及陆源的、细粒的凝灰岩碎屑。白云石普遍发育"雾心亮边"和"环带"等交代残余结构,非传统的沉积成因;从岩层厚度以及矿物组成等判断,不是热水成因。元素分析表明,随着白云石化成岩作用强度的增加以及外部流体的参与,岩石化学组分(包括主量元素如Fe、Mn和微量元素)或富集、或流失亏损,呈规律性变化。白云质岩中的Yb/Ca与Yb/La比值分布在岩浆成因的范围内。综合分析表明,研究区的白云质岩的交代原始物质为凝灰物质,堆积之后发生蚀变、方解石化,在镁离子参与下进而发生不均匀白云石化。The dolomitic rocks of the Permian Fengcheng Formation are the most significant hydrocarbon reservoir rocks in Wuerhe—Xiazijie area in the Junggar Basin.About a hundred milliontons of oil （3P） reserves have been found.On the basis of predecessor＇s studies,unifying petrology and geochemistry methods,this article explores origin of the dolomitic rocks,and provides a scientific geological foundation for exploration and evaluation of this tight oil reservoir in the northwestern margin of the Junggar Basin.By X-ray diffraction,cathodoluminescence and scanning electron microscope,and microscopic identification of rock thin sections,we concluded that the dolomitizing host rock consists of tephra and tuffaceous debris of terrigenous origin.The obvious residual texture of replacement in the dolomite minerals under microscope indicates that the dolomitic rocks in the area had not been deposited initially.Strata thickness and mineral assemblage both are the important evidences that reject the viewpoint of hydrothermal jet.Element analyses indicate that,with intensified dolomitization,rock chemical compositions had regularlychanged.The ratios of Yb/La and Yb/Ca of special rocks fall within the scope of carbonatite,indicating that the dolomitizing initial rock has obvious magmatogene.Comprehensive analysis shows that,the dolomitizing initial materials are volcanic ashes.After sedimentation,alteration and calcilization,the volcanic ashes were unequally replaced by Mg2＋.

关 键 词：白云质岩 火山物质 成岩蚀变 风城组 乌尔禾—夏子街地区 准噶尔盆地 

分 类 号：P588.245[天文地球—岩石学] P534.46[天文地球—地质学]