巴西巴拉纳(Parana)盆地下二叠统伊拉蒂组(Irati)油页岩地球化学特征及地质意义

Lower Permian Irati Formation Oil Shale Geochemical Features and Geological Significance in Parana Basin,Brazil

巴西巴拉纳(Parana)盆地是南美洲重要的含油气盆地,除了丰富的石油资源外,其所蕴藏的浅层可商业开采的油页岩资源也备受瞩目。目前,对巴拉纳盆地下二叠统伊拉蒂组油页岩的研究多集中在工业利用等方面,对其地球化学特征和油页岩形成条件等方面研究甚少,且尚无国内一手研究结果。通过对露天矿油页岩样品进行了总有机碳含量(TOC)、岩石热解、生物标志化合物、有机显微组分鉴定、主微量元素测定、全岩及黏土X衍射和工业分析等方面的测试,分析了巴拉纳盆地油页岩地球化学特征,并对有机质来源和沉积环境进行判别。结果显示,巴拉纳盆地油页岩具有较高的有机质丰度,TOC(质量分数)可达23.2%,有机质类型为I型,有机质来源以藻类体为主,辅以陆源高等植物;正构烷烃呈低碳数为主的单峰型分布;规则甾烷相对含量呈C_(29)>C_(27)>C_(28);沉积地球化学环境敏感参数显示,伊拉蒂组油页岩沉积时期CIA为72,整体上呈温暖湿润的气候背景,温湿气候背景下伴随着较高的生物生产力,同时缺氧的水体环境有利于有机质的保存,促进了伊拉蒂组优质油页岩的形成。

The Brazilian Parana Basin is a major oil and gas bearing basin in South America.Besides abundant petroleum resources,the basin contained shallow oil shale resources can be commercially exploited has also attracted much attention.At present,the study on lower Permian Irati Formation oil shale has mainly concentrated in industrial utilization,less attention paid on geochemical features and oil shale formation conditions,so that without their domestic first-hand research achievement up to now.Through surface mine oil shale samples TOC content,rock pyrolysis,biomarker compound,organic maceral identification,principal trace elements determination,whole rock and clay X-ray diffraction and proximate analysis,the paper has analyzed oil shale geochemical features,carried out organic matter source and sedimentary environment determination.The results have shown that oil shale in the basin has higher organic matter abundance,TOC content can be 23.2%as high,organic matter type belongs to category I,mainly from alginite supplemented by terrestrial higher plants.Normal paraffins present mainly low carbon number unimodal distribution.Relative amount of regular sterane presents C_(29)>C_(27)>C_(28).Sedimentary geochemical environment-sensitive parameters have shown that during Irati Formation oil shale sedimentation period,chemical index of alteration(CIA)is 72,on the whole presented warm,humid climate setting,under this setting accompanied by a higher biological productivity,meanwhile anoxic water body environment is favor to organic matter preservation,thus promoted Irati Formation high quality oil shale formation.