致密砂岩碳酸盐矿物SEM-CL和EPMA矿物学表征及其成岩意义——以川西坳陷须家河组为例  

SEM-CL and EMPA Mineralogical Characterization of Authigenic Calcite Cement in Tight Gas Sandstone and Implications for Diagenesis:Case study of Xujiahe Formation in western Sichuan Basin,China

作　　者：余瑜[1,2] 林良彪[1,2] 李真 孟万斌[1] 童馗 梁庆韶 YU Yu;LIN LiangBiao;LI Zhen;MENG WanBin;TONG Kui;LIANG QingShao(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;John de Laeter Centre,Faculty of Science and Engineering,Curtin University,GPO Box U1987,Perth,WA 6845,Australia)

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),成都610059 [2]成都理工大学沉积地质研究院,成都610059 [3]John de Laeter Centre,Faculty of Science and Engineering,Curtin University,GPO Box U1987,Perth,WA 6845,Australia

出　　处：《沉积学报》2023年第5期1468-1477,共10页Acta Sedimentologica Sinica

基　　金：国家自然科学基金项目(42202128);油气藏地质及开发工程国家重点实验室(成都理工大学)开放基金项目(PLC20210110)。

摘　　要：扫描电镜—阴极发光(SEM-CL)可通过同时分析矿物的微观结构和阴极发光特性来反映成岩机制及流体来源,但碳酸盐矿物在SEM-CL下的发光特性及其影响因素尚不明确。应用光学显微镜阴极发光(OM-CL)、电子探针(EPMA)和SEM-CL等技术手段,以川西坳陷须家河组致密砂岩中碳酸盐矿物为研究对象,分析碳酸盐矿物在OM-CL和SEM-CL下发光特性的差异,评估影响碳酸盐矿物SEM-CL发光特性的因素,探讨砂岩中方解石胶结物的成岩意义。结果表明,相比OM-CL,SEM-CL在区分碳酸盐岩屑和碳酸盐胶结物方面具有更高的灵敏度。当Mn/Fe值低于0.1或Mn/Fe值介于0.1~0.5且Fe含量低于0.1%时,碳酸盐矿物具有中低强度的SEM-CL发光强度;当Mn/Fe值高于0.5且Fe含量高于0.1%时,碳酸盐矿物在SEM-CL照射下几乎不发光。Mn/Fe值和Fe含量是影响SEM-CL照射下碳酸盐矿物发光强度的主要因素。阴极发光分析和EPMA元素组成面扫描分析表明,方解石胶结物的元素分布是均质的,形成于同一成岩世代,晚于长石等矿物的溶解。岩屑砂岩和岩屑石英砂岩的方解石胶结物具有相同的来源,表现为高Mn/Fe特征;钙屑砂岩的方解石胶结物具低Mn高Fe特征,成分组成与白云石岩屑相似,推测流体可能受到白云石岩屑溶解的影响。Scanning electron microscope-cathodoluminescence(SEM-CL)analysis is an effective tool for tracing the diagenesis associated with fluid flow in buried material by determining both the micro-texture and the CL response of authigenic minerals.However,neither the luminescence of carbonate minerals nor how their elemental compositions influence CL response is not clear.In this study,the CL response of carbonate minerals and its correlation with ele⁃ment compositions were observed when subjected to optical microscope-CL(OM-CL)and SEM-CL illumination,electron probe microanalysis(EPMA)and SEM-CL were used to analyze tight gas sandstone samples from the Xujia⁃he Formation in the western Sichuan Basin,China.The results suggest that SEM-CL distinguishes carbonate grains from carbonate cements with greater sensitivity than OM-CL.SEM-CL images generally showed that carbonate miner⁃als with Mn/Fe values lower than 0.1 have low-to moderate intensity luminescence.This was also apparent in Mn/Fe values of 0.1 to 0.5 with<0.1%Fe content,but carbonate minerals with Mn/Fe>0.5 and Fe content<0.1 barely showed a visible CL response.The Mn/Fe ratio and Fe content were found to have the greatest effect on CL.The inte⁃gration of SEM-CL and OM-CL with element mapping showed that the calcite cement is homogeneous,suggesting a single episode of calcite precipitation after the dissolution of feldspar.Sublitharenitic and litharenitic calcite cements have the same/similar source of diagenetic fluid that is indicated by high Mn/Fe values.The calcite cement in calcare⁃naceous sandstone showed low Mn and high Fe contents similar to dolomite rock fragments,suggesting that the fluid may have been influenced by the dissolution of dolomite rock fragments.

关 键 词：方解石胶结物 扫描电镜—阴极发光 成岩作用 致密砂岩 须家河组 四川盆地 

分 类 号：P618.13[天文地球—矿床学]