摘要
利用X射线衍射和扫描电子显微镜及能谱仪开展了岩石特征、矿物组成、微观结构特征和元素与矿物成分分析,研究了中上扬子地区五峰组—龙马溪组下段富有机质硅质页岩的成因及其与页岩气富集的关系。五峰组和龙马溪组下段硅质页岩中的脆性矿物石英含量较高,多在45%以上,最高达88%,而黏土矿物含量较低;少数页岩样品黏土矿物含量较高,同时碳酸盐矿物含量也较高,石英含量则较低。显微镜下发现富含石英的硅质页岩中大多存在大量团块状生物碎屑,并作为骨架颗粒与其他矿物基质胶结在一起,结构致密,而富含黏土矿物的页岩则多具水平层理和纹层理,未见生物碎屑。进一步的显微分析发现,富含石英的硅质页岩中的生物碎屑具有清晰的外形轮廓和圈层状生长结构及放射状针刺结构,显示出明显的硅质生物放射虫的形貌特征,且主要由硅和氧两种元素组成的能谱分析结果证实了确属放射虫。多种元素的面分布特征进一步反映出陆源物质的输入较少,而且海底的热液活动也极为有限的特征,指示页岩中硅质主要来源于放射虫生物骨架,为该段硅质页岩的生物成因提供了充分证据。放射虫大量发育的基本条件是海水中营养元素-溶解态硅富集,浮游藻类在该环境下易于大量勃发,高的初级生产力条件为硅质页岩中有机质的富集奠定了重要物质基础。放射虫成因的硅质页岩还有利于页岩中原生无机孔隙和次生有机孔隙的保持和保存,对页岩气的富集有极为重要的控制作用。
In order to study the origin of organic matter enriched siliceous shale from Wufeng-Longmaxi Formation in the Middle and Upper Yangtze region,and its relationship with shale gas accumulation,rock features,mineral composition,micromorphology,structural characteristics and chemical elements were analyzed by X-ray diffraction,scanning electron microscope（SEM）and energy disperse spectroscopy methods.Quartz content was found to be relatively high,mostly above 45% and 88% being the highest,while clay mineral content was relatively low in the Wufeng Formation and lower section of the Longmaxi Formation.Abundant biological residue and debris can be seen in the siliceous shales under SEM,they acted as skeleton particles and bound tightly with the mineral matrix,resulting in a highly compact rock structure;clay mineral enriched shales,whereas,developed horizontal beddings.Under SEM,the observed circular layered growth structure and needle structures of the biogenic materials clearly showed the characteristics of radiolarian morphology.The chemical compositions of these structures were shown to be mainly consisted of silicon and oxygen elements by energy spectrum analysis,further providing proofs to their radiolarian origin.Moreover,surface distribution of elements indicated the terrigenous input and hydrothermal activity were very limited,implying silica was mainly from radiolarian skeleton.Altogether we now have sufficient evidence to support a biogenic origin for siliceous shales in the region.High soluble silica concentration is prerequisite for radiolarian enrichment,it creates an environment for algae proliferation which leads to organic matter accumulation.Biogenic silicon was also favorable for the preservation of primary inorganic and secondary organic pores.Enrichment of biogenic silica,therefore,plays an important role in shale gas accumulation in the Wufeng and Longmaxi Formations.
作者
卢龙飞
秦建中
申宝剑
腾格尔
刘伟新
张庆珍
LU Longfei;QIN Jianzhong;SHEN Baojian;Tenger;LIU Weixin;ZHANG Qingzhen(SINOPEC Key Laboratory of Hydrocarbon Accumulation,Wuxi 214151,China;Wuxi Research Institute of Petroleum Geology,Research Institute of Petroleum Exploration and Production,SINOPEC,Wuxi 214151 China)
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2018年第4期226-236,共11页
Earth Science Frontiers
基金
国家自然科学基金项目(U1562106)
国家油气重大专项(2016ZX05036002)
中石化技术开发项目(P15097)
关键词
生物成因
硅
石英
放射虫
硅质页岩
biogenic
silica
quartz
radiolarian
siliceous shale
