西藏措勤盆地上二叠统白云岩成因及储集性研究

发布时间：2018-04-08 13:03

  本文选题：白云岩　切入点：二叠系　出处：《成都理工大学》2016年博士论文

【摘要】：措勤盆地自古生界至白垩纪发育巨厚的海相碳酸盐岩和碎屑岩沉积,是青藏高原第二大海相沉积盆地。志留系扎弄俄玛组以及二叠系木纠错组砂糖状白云岩油苗的发现证实这一地区古生界存在油气运移和聚集的过程,具备良好的油气勘探前景。论文通过前人资料收集、野外地质调查及室内测试分析,对措勤盆地古生代晶粒状白云岩进行了详细研究。首先通过显微观察,将白云石划分为A型(它形)、S型(半自形)以及E型(自形)。进而根据环带结构划分为单环带和多环带白云石,其中单环带白云石包括雾心亮边及亮心雾边两种类型。采用阴极发光及显微荧光详细研究了S型雾心亮边白云石、S型亮心雾边白云石、E型多环带白云石以及E型鞍状白云石的发光特征。结果显示雾心亮边白云石荧光识别精度高于阴极发光,部分晶体可以观察到多个荧光环带。电子探针分析表明,白云石核心一般SrO含量相对较高,FeO和MnO含量低。多环带及鞍状白云石具有极高的FeO含量,且高值均集中在内环带。环带白云石由边缘向核心Mg/Ca比值普遍具有高低波动的特征,鞍状白云石边缘Mg/Ca比值高于核心。白云石包裹体均一温度主要分布于120~180℃之间,盐度均值远高于现代海水盐度,白云岩的形成经历了高温高盐度的演化过程。微区同位素测试结果显示单环带白云石δ13C值介于-0.18~+0.40‰,δ18O值-2.30~-4.46‰;多环带白云石δ13C值介于-0.22~-2.38‰,δ18O值-2.58~-7.75‰。通过氧同位素分馏方程计算得到白云石化流体的δ18OSMOW值介于+6~+16‰,形成单环带白云石的流体来自原始沉积海水的蒸发残余或与地下卤水的混合,多环带白云石δ18OSMOW值偏低,可能受到深部热液的改造或地下淡水的补给。白云岩经历了两期白云石化作用:第一期为回流渗透白云石化作用,海水通过粒间孔或晶间孔渗透到碳酸钙沉积物或石灰岩地层,在成岩过程中通过离子置换形成第一世代微—粉为主的白云石。第二期埋藏白云石化作用占主导,形成以粉—细晶为主,具有雾心亮边和亮心雾边结构的第二世代白云石,同时在流体作用较强的部位沉淀多环带结构的第三世代白云石。储集性研究表明,白云岩储层非均质性强,溶蚀孔洞和裂缝发育,可划归裂缝—溶蚀孔隙型储层体系。建设性成岩作用主要包括白云石化作用、溶蚀作用以及破裂作用。白云岩中发育两期油气包裹体,第一期主要分布于方解石脉中,以液态烃包裹体为主,与其伴生的含烃盐水包裹体平均均一温度130.8℃。第二期主要分布于白云石中,以气态烃包裹体为主,与其伴生的含烃盐水包裹体平均均一温度148.2℃。大规模油气充注发生在埋藏白云石化作用之后,木纠错组含油白云岩可能属于“新生古储”型油气藏。
[Abstract]:From Paleozoic to Cretaceous, the Cooqin Basin is the second largest marine sedimentary basin in Qinghai-Xizang Plateau.The discovery of granulated dolomite oil seedlings in Zhanomar formation of Silurian system and the error-correcting group of Permian shows that there is a process of hydrocarbon migration and accumulation in the Paleozoic in this area, which has a good prospect for oil and gas exploration.Based on the previous data collection, field geological investigation and laboratory test and analysis, the Paleozoic granular dolomite in Cuoqin Basin is studied in detail.Firstly, dolomite is divided into A type (S type) and E type (E type) by microscopic observation.According to the structure of the annular zone, dolomite can be divided into single-ring zone and multi-ring zone dolomite, in which the single-ring dolomite includes two types: bright edge of fog center and bright mist edge of bright core.The luminescence characteristics of S type fog core bright edge dolomite, S type bright core mist edge dolomite E type multi ring dolomite and E type saddle dolomite were studied in detail by cathodic luminescence and microfluorescence.The results show that the fluorescence recognition accuracy of dolomite with bright edge is higher than that of cathodoluminescence, and several fluorescence bands can be observed in some crystals.Electron probe analysis shows that the general SrO content of dolomite core is relatively high, and the content of Feo and MnO is relatively low.The polycyclic zone and saddle dolomite have extremely high FeO content and the high values are concentrated in the inner ring zone.The Mg/Ca ratio of dolomite from edge to core generally fluctuates in the annular zone, and the Mg/Ca ratio at the edge of saddle dolomite is higher than that in core.The homogeneous temperature of dolomite inclusions is mainly distributed between 120 鈩，

本文编号：1721728