摘要
鄂尔多斯盆地奥陶系风化壳储层受不同期次方解石影响,厘清方解石成因及其影响有助于明确储层形成机理。对盆地富县地区奥陶系风化壳膏模孔与溶缝内充填的方解石进行了矿物学、地球化学及同位素年代学分析,结果表明,方解石可分为白色原生方解石、红色次生方解石、白色次生方解石三类。其中,充填于膏模孔与溶缝内的白色原生方解石,溶孔方解石解理发育,溶缝方解石解理不发育,地球化学显示具有明显的Ce负异常,少数溶孔充填方解石具Eu正异常,阴极发光呈红色、橙红色,U-Pb年龄分别为333.3±3.3 Ma和332.8±3.5 Ma,表明该类方解石形成于早石炭世地表-近地表环境,石膏被大气淡水溶蚀形成Ca^(2+),在膏模孔及溶缝处与富含CO_(3)^(2-)的大气淡水反应而成。红色方解石为交代去白云石化次生方解石,多保留白云石晶型,地球化学显示高Mn、低Sr、高Sr同位素以及C、O同位素负偏的特征,阴极发光呈橘红色,未能获得定年数据,系地表-近地表环境中大气淡水等摩尔交代白云石晶体而成。白色次生方解石呈嵌晶状,中粒结构,解理发育,阴极发光呈橘红色,具有高Sr、高Sr同位素、Ce负异常、O同位素相对稳定、C同位素发生负偏的特征,U-Pb年龄为212.0±19.0 Ma,表明该类方解石在晚三叠世排烃期由酸性流体与Ca^(2+)反应而成。各类方解石是不同成岩阶段不同成岩流体的产物,易形成于相对低洼的滞水地带,导致岩石孔隙度降低,因此寻找有效储层应关注古岩溶地貌高部位。
The Ordovician weathered crust reservoir in the Ordos Basin is affected by calcites of different stages,so clarifying the genesis and influence of calcites can help to understand the mechanism of reservoir formation.Minera-logical,geochemical and isotope chronological results of calcites from the Ordovician weathered crusts in the Fuxian area of the Ordos Basin demonstrate that these calcites can be divided into white primary calcite,red secondary calcite and white secondary calcite.The white primary calcite filled in the pores and crevices of the paste mold,whereas the cleavage of calcite in the dissolved pores is much more developed than those in the dissolved seams.Geochemistry shows obvious negative Ce anomalies,a few calcites filled in the pores have positive Eu anomalies.They have red and orange-red cathodoluminescence,and their U-Pb ages are 333.3±3.3 Ma and 332.8±3.5 Ma,respectively,indicating that this type of calcite was formed in the early Carboniferous near surface environment.Gypsum was dissolved by atmospheric freshwater to form Ca^(2+),which reacted with atmospheric freshwater rich in CO_(3)^(2-)at the gypsum mold pores and dissolution fractures.Red calcite is the secondary calcite of metasomatic dedolomitization,with dolomite crystal type mostly and orange-red cathodoluminescence.It is formed by metasomatic dolomite crystals in the atmospheric freshwater equimolarly from surface to near-surface environment,with high Mn,low Sr,high Sr isotopes and negative C and O isotopes.White secondary calcite is poikilitic,and medium-grained crystals,with developed cleavage,orange-red cathodoluminescence,high Sr concentration and high Sr isotopes,negative Ce and C anomalies,relatively stable O isotope,and U-Pb age of 212.0±19.0 Ma.The results indicate that this type of calcite was formed by the reaction of acidic fluids with Ca^(2+)during the Late Triassic hydrocarbon expulsion period.All kinds of calcite are the products of different diagenetic fluids in different diagenetic stages,which are easy to develop in the relative low-lying stagnant areas and result in the reduced rock porosity.Therefore,more attention should be paid to the high parts of paleo-karst geomorphology for effective reservoirs.
作者
任静
苏中堂
黄浩
高星
吴浩文
魏柳斌
裴文超
REN Jing;SU Zhong-tang;HUANG Hao;GAO Xing;WU Hao-wen;WEI Liu-bin;PEI Wen-chao(College of Earth Science,Chengdu University of Technology,Chengdu 610059,China;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;Research Institute of Exploration and Developmen,PetroChina Changqing Oilfield Company,Xi'an 710018,China;National Engineering Laboratory for Exploration and Development of LowPermeability Oil and Gas Fields,Xi'an 710018,China)
出处
《岩石矿物学杂志》
北大核心
2025年第2期345-360,共16页
Acta Petrologica et Mineralogica
基金
中国石油长庆油田重大科技专项(CQZDZX2021)
中石油攻关性应用性科技专项(2023ZZ16YJ01)。
