济阳坳陷古近系沙河街组湖相富有机质页岩白云石成因及成岩演化  

Origin and diagenetic evolution of dolomites in Paleogene Shahejie Formation lacustrine organic shale of Jiyang Depression,Bohai Bay Basin,East China

作　　者：滕建彬 邱隆伟[1] 张守鹏[2,3] 马存飞[1] TENG Jianbin;QIU Longwei;ZHANG Shoupeng;MA Cunfei(School of Geosciences,China University of Petroleum(East China),Qingdao 266580,China;Exploration and Development Research Institute,Shengli Oilfield Company,Sinopec,Dongying 257015,China;Key Laboratory of Shale Oil/Gas Exploration and Production,Sinopec,Beijing 100083,China)

机构地区：[1]中国石油大学(华东)地球科学与技术学院,山东青岛266580 [2]中国石化胜利油田分公司勘探开发研究院,山东东营257015 [3]中国石化页岩油气勘探开发重点实验室,北京100083

出　　处：《石油勘探与开发》2022年第6期1080-1093,共14页Petroleum Exploration and Development

基　　金：国家自然科学基金项目(42172153,41802172);中国石化重点实验室项目“济阳坳陷古近系细粒沉积特征与古湖泊演化”(KL21042);胜利油田分公司项目“东营凹陷沙四段页岩沉积成岩事件与孔缝成因研究”(YKS2101)。

摘　　要：通过岩石学、X衍射全岩成分分析、稳定碳氧同位素组成分析,以及微量元素和稀土元素组成分析,对济阳坳陷古近系沙河街组页岩中白云石的成因进行研究。结果表明,研究区沙河街组湖相富有机质页岩中的白云岩发育规模小,可识别出3种白云石矿物:原生白云石(D1)、准同生白云石(D2)和铁白云石(Ak)。D1具有原生球形白云石的结构,高镁高钙,白云石有序度为0.3~0.5,且普遍具有外缘次生加大现象和内核溶蚀孔共存的特征;D2有序度为0.5~0.7,具有次生加大、高镁高钙和含铁锰元素的特点;Ak具有高有序度(0.7~0.9)、菱形晶、高镁、高钙和高铁的特征。在利用碳氧同位素组成和稀土元素分馏特征佐证泥晶方解石为原生成因的基础上,根据共生白云石和泥晶方解石之间的氧同位素组成分馏方程,计算得到研究区页岩中白云石的形成温度为36.76~45.83℃,属于湖相低温白云石。此外,基于原生和准同生白云石晶体的熟化生长机制,恢复了与研究区沙河街组湖相页岩成岩环境相对应的白云石成岩序列和白云石化作用进程。The origin of dolomite in Shahejie Formation shale of Jiyang Depression in eastern China were studied by means of petrologic identification,compositional analysis by X-ray diffraction,stable carbon and oxygen isotopic composition,and trace element and rare earth element analyses.The results show that the development of dolomite is limited in the lacustrine organic rich shale of Shahejie Formation in the study area.Three kinds of dolomite minerals can be identified:primary dolomite(D1),penecontemporaneous dolomite(D2),and ankerite(Ak).D1 has the structure of primary spherical dolomite,high magnesium and high calcium,with order degree of 0.3-0.5,and is characterized by the intracrystalline corrosion and coexistence of secondary enlargement along the outer edge.D2 has the characteristics of secondary enlargement,order degree of 0.5-0.7,high magnesium,high calcium and containing a little iron and manganese elements.Ak is characterized by high order degree of 0.7-0.9,rhombic crystal,high magnesium,high calcium and high iron.The micritic calcite belongs to primary origin on the basis of the carbon and oxygen isotopic compositions and the fractionation characteristics of rare earth elements.According to the oxygen isotopic fractionation equation between paragenetic dolomite and calcite,it is calculated that the formation temperature of dolomite in the shale is between 36.76-45.83℃,belonging to lacustrine low-temperature dolomite.Based on the maturation and growth mechanism of primary and penecontemporaneous dolomite crystals,a dolomite diagenetic sequence and the dolomitization process are proposed,which is corresponding to the diagenetic environment of Shahejie Formation shale in the study area.

关 键 词：济阳坳陷 古近系沙河街组 富有机质页岩 白云石成因 同位素分馏 稀土元素 成岩演化 白云石有序度 

分 类 号：TE122.1[石油与天然气工程—油气勘探]