薄层介壳灰岩中方解石沉淀模式及致密储层成因——以川北下侏罗统东岳庙段为例  

Model of Calcite Precipitation in a Shell Limestone Interlayer and Densification of the Dongyuemiao Reservoir(Lower Jurassic)in the Northern Sichuan Basin

作　　者：冯明友[1,2] 罗振宇 刘小洪 祝海华[1] 曾德铭[1] 王兴志[1,2] 张芮[3] 曹娟 谢圣阳 FENG MingYou;LUO ZhenYu;LIU XiaoHong;ZHU HaiHua;ZENG DeMing;WANG XingZhi;ZHANG Rui;CAO Juan;XIE ShengYang(School of Geoscience and Technology,Southwest Petroleum University,Chengdu 610500,China;Southwest Petroleum University,Division of Key Laboratory of Carbonate Reservoir,CNPC,Chengdu 610500,China;Exploration and Development Institute,PetroChina Southwest Oil and Gas Field Company,Chengdu 610213,China)

机构地区：[1]西南石油大学地球科学与技术学院,成都610500 [2]中国石油碳酸盐岩储层重点实验室西南石油大学分室,成都610500 [3]中国石油西南油气田公司勘探开发研究院,成都610213

出　　处：《沉积学报》2025年第1期301-313,共13页Acta Sedimentologica Sinica

基　　金：国家科技重大专项(2017ZX05001-001);中国石油—西南石油大学创新联合体科技合作项目(2020CX050103)。

摘　　要：【目的】川北地区侏罗系自流井组东岳庙段为典型湖相致密页岩油储层,富有机质页岩中发育多套薄层介壳灰岩夹层,其间发育多期裂缝、方解石胶结以及溶蚀作用,储层致密化过程及富集规律不清。亟需进一步揭示介壳灰岩夹层历经的埋藏—成岩序列,探讨方解石形成与页岩油气关系。【方法】结合详细岩心观察、铸体薄片、电子探针成分分析及埋藏史—热演化史等,针对方解石矿物产状、主/微量元素及共生矿物特征开展深入分析。【结果】川北地区东岳庙段介壳灰岩夹层中发育细—中粒介壳重结晶方解石、脉状—透镜状纤维方解石、交代—溶蚀状微—亮晶方解石、含介壳泥岩中纤维状方解石、泥质介壳灰岩及含泥介壳灰岩中微晶粒状方解石、介壳灰岩孔缝中充填亮晶方解石等六种类型方解石,并对应于(1)早成岩A期沉积物重结晶成因、(2)早成岩B期与富有机质页岩生排烃有关的纤维状方解石、(3)中成岩A期溶蚀—再沉淀方解石及(4)中成岩B期方解石共四期胶结作用,方解石中Fe、Mn、Sr等元素含量与其形成时间及期次关系密切。【结论】多期方解石胶结是导致东岳庙段介壳灰岩储层致密化的主要原因,流体超压形成的纤维状方解石既引起储层致密化亦为后期溶蚀作用奠定一定基础,成岩中期的方解石沉淀则进一步降低孔隙度。方解石沉淀导致的储层致密化约束了页岩油时空分布。[Objective]Thin-layered shale and shell limestone are beneficial for determining the properties of the shale-oil reservoir of the Dongyuemiao member of the Ziliujing Formation(Lower Jurassic)in the northern Sichuan Basin.It is found that the shale and shell limestone have developed various types of fractures,calcite veins,and dis-solution.Our aim is to decipher the burial and diagenetic sequence of the shell limestone interlayers,and discuss the relationship between hydrocarbon accumulation and the formation of calcite and reservoir densification.[Methods]In our study we use detailed core observations,microscopic section observations,and the electron probe composition,trace elements,and paragenetic minerals are determined.[Results]The results show that seven types of calcite oc-cur in the organic-rich shale of the Dongyuemiao member according to their morphology,staining,and occurrence condition,such as:(1)recrystallized fine-medium crystalline calcite(C1)in the shell limestone;(2)noddle-lenticular fibrous calcite along the edge of the shell limestone(C2);(3)micro-sparry calcite,which occurs along the edge of shell limestone(C3);(4)fibrous calcite in the shell mudstone(C4);(5)microcrystalline granular cal-cite in the argillaceous shell limestone(C5);(6)microcrystalline granular calcite in the muddy shell limestone(C6);and sparry calcite in pores and/or fractures(C7).Besides,the microfractures in the shell-limestone are deve-loped,which can be obviously divided into F1(with low opening degree and reluctantly cut through the shell),F2(with curved fracture surface and occurred associated with fibrous calcite),and F3(obviously break the shell).The formation sequence of minerals such as fractures and calcite is:C1+pyrite→F1→F2→C2/C4→C3→quartz+kaolinite→F3→C5/C6+asphalt→C7.The major elements in the calcite and the division of phases indicate that C1 to C3 calcite,which has a low content of FeO and a high content of SrO,may have formed during an early diagenetic stage.The contact relationship between C2

关 键 词：川北地区 侏罗系 东岳庙段 页岩油 方解石胶结物 

分 类 号：P588.245[天文地球—岩石学]