歧口凹陷古近系沙一段沉积环境及白云岩成因机理分析

发布时间：2018-05-05 07:48

本文选题：歧口凹陷 + 沙一段　；参考：《吉林大学》2017年硕士论文

【摘要】：歧口凹陷位于渤海湾盆地,分布了大面积的湖相碳酸盐岩,具有很好的油气勘探前景。随着北大港、板桥以及齐家务等地区的开发生产,歧口凹陷展示出了巨大的生油潜力,在对歧口凹陷西侧井位的钻探过程中,发现沙一段地层的白云岩中含有大量油气资源。因此,对歧口凹陷古近系沙一段白云岩进行研究可以进一步挖掘该地区的潜力,很有现实意义。本文应用扫描电镜、阴极发光、X射线衍射等分析测试方法,结合锶同位素、碳氧同位素、主微量元素、稀土元素等地球化学特征,对歧口凹陷沙一段进行了岩石类型、沉积环境、成岩环境以及白云岩成因方面的研究,并对该时期的海侵事件进行了深入的探讨。歧口凹陷沙一段主要发育泥-微晶灰质白云岩、泥-微晶白云岩、亮晶生物碎屑灰质白云岩等,这些碳酸盐岩多和泥页岩互层产出。通过其纵向的岩性对比,认为沙一段时期研究区水体不断上升,水动力越来越弱,还原性不断增强。整体上,研究区白云岩轻稀土富集、重稀土相对亏损;δCe与湖相白云岩极为接近;δLa与Y/Ho值为负相关关系,REE与Al为正相关关系、与Ca为负相关关系。以上证据表明,研究区白云岩形成于湖相沉积环境。此外,白云岩δ~(13)C-δ~(18)O相关性很高,投点呈条带状线性分布,两者具有同步增加的特点,反映歧口湖盆在该时期封闭性较强。研究区发现狭口螺等海相古生物化石;白云岩Z值、M值、Sr/Ba、V/Ni、Th/U指示咸水环境;~(87)Sr/~(86)Sr值与海水极为接近;大部分样品的δLa、δY、Y/Ho值超出湖相白云岩的区间,并且向海相白云岩靠近,表现出极强的海水特征。综合以上证据,认为本区在沙一段时期发生过海侵事件。海侵为湖盆带来了大量的Mg~(2+),导致了湖盆的咸化,并且使湖盆的PH值升高,这些因素促成了白云岩化的发生。六间房与齐家务地区的白云岩发桔红色光,较为明亮;碳氧同位素分析表明其形成于浅埋藏环境,没有受到甲烷化作用的影响;有序度和Mg/Ca值都很低。综合分析认为该地区的白云岩是渗透回流模式形成的。歧口与扣村地区的白云岩整体发光微弱,甚至不发光;碳氧同位素反映白云岩形成于浅埋藏环境,并且受到很强的甲烷化作用;白云石有序度低但是Mg/Ca值整体比齐家务地区高,反映其经历了更为充分的成岩作用。综合分析认为该地区的白云岩为埋藏成因。
[Abstract]:Qikou sag is located in the Bohai Bay basin and has a large area of lacustrine carbonate rocks, which has a good prospect of oil and gas exploration. With the development and production of Beidagang, Banqiao and Qijiao areas, Qikou sag has shown great oil generation potential. During the drilling of wells in the west side of Qikou Sag, it was found that there are a lot of oil and gas resources in dolomite in the formation of Shayi formation. Therefore, the study of dolomite in the first member of the Paleogene Sha in Qikou Sag can further exploit the potential of this area, which is of great practical significance. In this paper, the rock types of the first member of the Sha member in Qikou depression have been studied by means of scanning electron microscope, cathodoluminescence X-ray diffraction and geochemical characteristics of strontium isotope, carbon oxygen isotope, main trace element, rare earth element, etc. The sedimentary environment diagenetic environment and dolomite genesis are studied and the transgression events in this period are discussed. The mud-microcrystalline dolomite, mud-microcrystalline dolomite and lime-dolomite are mainly developed in the first member of Sha in Qikou Sag. These carbonate rocks are abundant and interbedded with shale. Through the longitudinal lithology comparison, it is considered that the water body in the study area is rising continuously, the hydrodynamic force is getting weaker and the reductivity is increasing. On the whole, the dolomite in the study area is enriched in light rare earth and relatively depleted in heavy rare earth; 未 ce is very close to lacustrine dolomite; 未 La is negatively correlated with Y/Ho value; REE is positively correlated with Al, and negatively correlated with Ca. The above evidence indicates that dolomite was formed in the lacustrine sedimentary environment. In addition, the correlation of 未 ~ (13) C ~ (-) ~ (18) O in dolomite is very high, and the distribution of the drop points is linear in a strip, which shows that the Qikou Lake basin is closed in this period. Marine paleontological fossils such as the narrow mouth snail were found in the study area. The Z value of dolomite and the value of S r / BaV / V / Ni / T / U indicate that the brackish water environment is very close to that of seawater, and the 未 La, 未 YTY / Ho values of most samples exceed the interval of lacustrine dolomite and are close to the marine dolomite. It shows very strong characteristics of sea water. Combined with the above evidence, it is concluded that transgression occurred in this area during a period of sand. The transgression brought a large amount of Mg~(2 to the lake basin, which led to the salinization of the lake basin and the increase of the PH value of the lake basin. These factors contributed to the occurrence of dolomitization. The dolomite in the six rooms and the domestic areas has bright orange light, and the carbon and oxygen isotopic analysis shows that it was formed in shallow burial environment and was not affected by methanation, and the order degree and Mg/Ca value are very low. It is considered that the dolomite in this area is formed by the permeation reflux model. The dolomite in Qikou and Jiucun areas is weak or even non-luminous; carbon and oxygen isotopes show that dolomite was formed in shallow burial environment and was strongly methanized; dolomite order is low but Mg/Ca value is higher than that in domestic areas. It reflects that it has experienced more sufficient diagenesis. It is considered that the dolomite in this area is the burial origin.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P618.13

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