摘要
下奥陶统蓬莱坝组白云岩是塔河油田油气勘探的重要接替领域,明确白云岩的沉积特征、成因机理对塔河油田的油气勘探与开发具有重要意义。综合岩心描述、薄片鉴定、扫描电镜、阴极发光及地球化学等分析手段,系统研究了塔河油田下奥陶统蓬莱坝组白云岩的地质地球化学特征及成因机制。结果表明:(1)研究区以晶粒白云岩为主,残余颗粒白云岩次之。泥—微晶白云石以他形为主,粉—中晶多呈半自形—自形,中—粗晶以异形为主;残余颗粒白云岩以粉—细晶为主,可见残余内碎屑结构。(2)阴极发光显示:泥—微晶呈暗淡蓝紫或暗褐色光;粉晶为暗淡紫红色;细—中晶具紫色核心、橙红色亮边环带结构;中—粗晶呈紫红与明亮棕红色环带发光。(3)泥—微晶白云岩主要为重稀土富集,δ^(18)O值波动大,^(87)Sr/^(86)Sr值接近早奥陶世海水值,指示高盐度蒸发海水的准同生白云石化作用;残余颗粒白云岩主要为残余内碎屑结构,属埋藏云化成因;粉晶白云岩、细—中晶白云岩稀土元素(REE)配分模式与同期泥晶灰岩类似,重稀土富集,δ^(18) O值跨度较大,^(87)Sr/^(86)Sr值部分高于同期海水锶同位素值,为浅—中埋藏云化叠加热液改造的产物;中—粗晶白云岩轻稀土相对富集,δ^(18) O值偏负,^(87)Sr/^(86)Sr值高于同期海水值,属碎屑岩层热液交代成因。
The dolomite of the Lower Ordovician Penglaiba Formation is an important successor field for oil and gas exploration in the Tahe oilfield.Clarifying the sedimentary characteristics and genetic mechanisms of the dolomite is of great significance for oil and gas exploration and development in the Tahe oilfield.Based on this,the geological and geochemical characteristics and genetic mechanisms of the dolomite in the Lower Ordovician Penglaiba Formation of the Tahe Oilfield were systematically studied through core description,thin section identification,scanning electron microscopy,cathodoluminescence,and geochemical analyses.The results showed that:(1)The study area was dominated by crystalline dolomite,followed by residual granular dolomite.Mud⁃microcrystalline dolo⁃mite was mainly anhedral.Silty-medium crystalline dolomite was mostly subhedral to euhedral.Medium-coarse crystalline dolomite was predominantly xenomorphic.Residual granular dolomite was mainly composed of siltyfine crystalline dolomite,showing residual intraclastic texture.(2)Cathodoluminescence showed that the mudmicrocrystalline dolomite emitted dull blue-purple or dark brown luminescence.Silty dolomite emitted dull purple⁃red luminescence.Fine-medium crystalline dolomite had a purple core with a bright orange⁃red rim-shaped band.Medium-coarse crystalline dolomite exhibited purple⁃red and a bright brown⁃red rim⁃shaped luminescent band.(3)Mud-microcrystalline dolomite was mainly enriched in heavy rare earth elements(REE),with largeδ^(18) O fluctuations and ^(87)Sr/^(86)Sr ratios close to those in the Early Ordovician seawater,indicating quasi⁃syngenetic dolo⁃mitization by high⁃salinity evaporative seawater.Residual granular dolomite was mainly characterized by residual intraclastic texture and its genetic mechanism was burial dolomitization.The REE distribution patterns of silty crystalline dolomite and fine-medium crystalline dolomite were similar to those of contemporaneous micrites,which were enriched in heavy REEs with largeδ^(18)O fluctuations.The ^(87)Sr/^(86)Sr values were partially higher compared with the strontium isotope values in contemporaneous seawater,indicating products of shallow-medium burial dolomitization superimposed with hydrothermal fluids.Medium-coarse crystalline dolomite was relatively enriched in light rare earth,with negativeδ^(18)O values and ^(87)Sr/^(86)Sr values higher than those in contemporaneous seawater,indicating formation by hydrothermal metasomatism related to clastic rock layers.
作者
徐勤琪
彭军
何成其
夏金刚
刘瑞
黄苇
XU Qinqi;PENG Jun;HE Chengqi;XIA Jingang;LIU Rui;HUANG Wei(Exploration and Production Research Institute,Northwest Oilfield Company,SINOPEC,Urumqi,Xinjiang 830011,China;School of Geoscience and Technology,Southwest Petroleum University,Chengdu,Sichuan 610500,China;Sichuan Provincial Key Laboratory of Natural Gas Geology,Chengdu,Sichuan 610500,China)
出处
《石油实验地质》
北大核心
2025年第4期805-819,共15页
Petroleum Geology & Experiment
基金
中国石化西北油田分公司勘探开发研究院测试分析项目“塔里木盆地碳酸盐岩储层发育机理与重点区带评价方法”(34400008-22-ZC0613-0064)资助。
关键词
白云岩
成因机理
蓬莱坝组
下奥陶统
塔河油田
dolomite
genetic mechanism
Penglaiba Formation
Lower Ordovician
Tahe Oilfield
