白云岩-蒸发岩共生体系白云石化过程研究:以鄂尔多斯盆地马家沟组为例  

Research on dolomitization process in dolomite-evaporite syngenetic system of the Majiagou Formation in Ordos Basin

作　　者：吴宇婷 甯濛 夏攀 乔占峰[4,5] 于洲 文华国[1,2,3] WU Yuting;NING Meng;XIA Pan;QIAO Zhanfeng;YU Zhou;WEN Huaguo(State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Chengdu University of Technology,Chengdu 610059,China;Institute of Sedimentary Geology,Chengdu University of Technology,Chengdu 610059,China;Chengdu University of Technology Research Branch,Key Laboratory of Carbonate Reservoir,CNPC,Chengdu 610059,China;PetroChina Hangzhou Research Institute of Geology,Hangzhou 310023,China;Key Laboratory of Carbonate Reservoir,CNPC,Hangzhou 310023,China)

机构地区：[1]油气藏地质及开发工程全国重点实验室(成都理工大学),四川成都610059 [2]成都理工大学沉积地质研究院,四川成都610059 [3]中国石油天然气集团有限公司碳酸盐岩储层重点实验室成都理工大学研究分室,四川成都610059 [4]中国石油天然气股份有限公司杭州地质研究院,浙江杭州310023 [5]中国石油天然气集团有限公司碳酸盐岩储层重点实验室,浙江杭州310023

出　　处：《古地理学报》2024年第4期895-910,共16页Journal of Palaeogeography：Chinese Edition

基　　金：国家自然科学基金项目(编号:42272133,42102136);中国石油天然气股份有限公司科学研究与技术开发项目(编号:2021DJ0503)共同资助。

摘　　要：鄂尔多斯盆地奥陶系马家沟组典型的白云岩-蒸发岩共生体系中白云岩储集层发育,前人围绕该白云岩储集层特征及形成机制开展了大量研究,但缺乏从白云岩-蒸发岩共生体系角度来探索白云石化过程及演化特征的研究。文中选取鄂尔多斯盆地东南缘西磑口剖面发育的2段白云岩-蒸发岩沉积序列(S1、S2)进行高精度连续采样,以沉积学、岩石学分析为基础,结合碳氧同位素、稀土元素及微量元素地球化学分析,识别出2类白云岩-蒸发岩共生组合,并对其白云石化流体性质、来源、演化及白云石化过程进行了详细研究。结果表明:(1)S1采样段发育Ⅰ型共生组合,主要由内碎屑颗粒白云岩—膏溶角砾白云岩—泥晶白云岩(含石膏假晶)—泥岩组成,代表强蒸发潮上带环境;S2采样段发育Ⅱ型共生组合,主要由薄-中厚层细晶白云岩—中层(颗粒)白云岩—泥质白云岩(含石膏假晶)—泥岩构成,代表潮间带—潮下带环境。(2)2种共生组合类型中白云岩的稀土配分模式与孔隙水的配分模式相似,均表现为中稀土(MREE)富集、Ce弱负异常—正常、Eu弱负异常—正常、δ^(13)C和δ^(18)O值无明显差别、Fe_(carb)和Mn_(carb)含量较高,推测其白云石化流体来源相同,为海水衍生的弱还原性孔隙水。(3)研究剖面由下至上从Ⅰ型共生组合到Ⅱ型共生组合沉积序列的垂向演化,反映了蒸发潮坪环境中共生体系的典型白云石化过程,即随着海平面上升,从S1段至S2段由潮上带准同生萨布哈白云石化演化为潮间带—潮下带渗透回流白云石化,Ⅰ型共生组合中白云岩的MREE和Fe_(carb)含量高于Ⅱ型共生组合白云岩,反映白云石化流体性质从富Fe^(2+)-Mn^(2+)、MREE向贫Fe^(2+)-Mn^(2+)、MREE的演化。研究认识丰富了共生体系下白云岩成因的基础理论,可为马家沟组油气勘探提供理论指导。The dolomite reservoir is developed in the typical dolomite-evaporite paragenetic system(DEPS)of the Ordovician Majiagou Formation in the Ordos Basin.Many researchers have conducted numerous studies on the characteristics and formation mechanism of dolomite reservoirs in the Majiagou Formation.However,limited research has been done on the dolomitization process and evolution characteristics from the perspective of DEPS.In this study,two dolomite-evaporite sedimentary sequences(S1 and S2)from the Xiweikou section on the southeast margin of the Ordos Basin were selected for high-precision continuous sampling.Through sedimentology and petrology analysis,as well as carbon-oxygen isotopes,rare earth elements(REEs)and trace elements,two types of dolomite-evaporite paragenetic assemblages were identified.A detailed study was conducted on the properties,sources,evolution of dolomitization fluid,and the dolomitization process.The results show that:(1)in the S1 sampling interval,a Type I paragenetic assemblage is present,consisting mainly of intraclast grain dolomite-dissolved gypseous breccias dolomite-dolomicrite bearing gypsum pseudocrystals-mudstone.This indicates a supratidal environment with strong evaporation.In the S2 sampling interval,a Type II paragenetic assemblage is observed,mainly composed of thin-medium thick layers of finely crystalline dolomite-medium(grain)dolomite-argillaceous dolomite bearing gypsum pseudocrystals-mudstone,representing an intertidal-subtidal environment.(2)The REE distribution patterns of dolomite in two types of paragenetic assemblages are similar to those of pore water,both showing enrichment of MREE,with slightly negative anomalies-normal of Ce and Eu.There is no significant difference betweenδ^(13)C andδ^(18)O,and the contents of Fe_(carb) and Mn_(carb) are relatively high.It is speculated that the sources of dolomitized fluid are the same,originating from weakly reducing pore water derived from seawater.(3)The sedimentary sequence in the studied geological section changes from ty

关 键 词：白云岩-蒸发岩共生体系 白云石化过程 稀土元素 马家沟组 鄂尔多斯盆地 

分 类 号：P588.24[天文地球—岩石学]