Characteristics of oil shale development and paleoenvironment restoration of Jurassic Yan’an Formation in southwestern Ordos Basin
-
摘要: 【目的】鄂尔多斯盆地西南缘侏罗系延安组发育多套与煤伴生和非伴生的油页岩,但是长期以来对本区油页岩的特征及其沉积环境研究相对缺乏。【方法】本文通过对研究区钻井岩心进行取样,开展低温干馏、岩石热解、主微量元素测定和气相色谱等实验,对油页岩的工业指标、地球化学特征和沉积古环境进行分析。【结果】研究区油页岩含油率为3.8%~6.7%,灰分质量分数为49.46%~75.58%,全硫为0.31%~2.29%,发热量为11.95 kJ/g(平均值);测井曲线呈现高伽马、高电阻率和低自然电位特征,明显区别于煤层和泥岩;有机质类型主要以Ⅱ2型为主,有机质丰度较高,整体处于未熟-低成熟阶段;总体属于中品质、硅质灰分、特低硫的油页岩。主量元素以SiO2和Al2O3为主,分别为48.26%(平均值)和17.57%(平均值),微量元素Sr、Th和U富集,Ni、V和Ba亏损,元素分析表明研究区有较多含钾矿物和镁铁成分,且稳定组分较高。【结论】通过古环境元素标志和饱和烃色谱分析认为有机质主要来源于混合有机质,古生产力中等,且沉积环境具有独特性,属于温暖湿润的贫氧陆相淡水洼地环境。分析各环境因素显示,氧化还原条件为有机质富集主要影响因素,建立了不同沉积时期的延安组油页岩演化沉积模式。研究成果为鄂尔多斯盆地西南缘侏罗系延安组油页岩勘探开发提供了重要理论指导和技术支撑。Abstract: [Objective]There are many sets of oil shale associated with coal and non-associated oil shale in the Jurassic Yan’an formation in the southwest of Ordos Basin, but the study on the characteristics and sedimentary environment of oil shale in this area has been relatively lacking for a long time. [Methods]Based on the oil shale samples from wells in the study area, the industrial index, geochemistry characteristics and sedimentary paleoenvironment of oil shale were studied by low-temperature retorting, rock pyrolysis, major and trace elements measurement and gas chromatography. [Results]The oil shale in study area oil-bearing ratio is 3.8% ~ 6.7%, the ash is 49.46% ~ 75.58%, the total sulfur is 0.31% ~ 2.29%, and the calorific value is 11.95 kJ/g (average value). The logging curves show the characteristics of high gamma, high resistivity and low natural potential, which is obviously different from coal bed and mudstone. The main type of organic matter was II2. The abundance of organic matter is high, and the whole is in the stage of immature-low maturity. It belongs to middle quality, siliceous ash and extra low sulfur oil shale. The main elements in the oil shale are SiO2 and Al2O3, which are 48.26% (average) and 17.57% (average) and the micronutrient Sr, Th, and U were enriched, and Ni, V, and Ba were depleted, indicating that there were more potassium-containing minerals and higher stable components in the study area. [Conclusion]Based on the analysis of paleoenvironmental element markers and saturated hydrocarbon chromatography, it is considered that the organic matter mainly comes from the mixed organic matter, ancient productivity is medium and the sedimentary environment is unique, which belongs to the warm and humid continental fresh water depression environment. The analysis of environmental factors shows that the redox condition is the main influencing factor of organic matter enrichment and the sedimentary model of oil shale evolution in Yan’an formation in different depositional periods is established. The research results provide important theoretical guidance and technical support for the oil shale exploration and development of the Jurassic Yan’an formation in the southwestern margin of Ordos Basin.
-
Key words:
- Ordos Basin /
- Yan’an Formation /
- oil shale /
- paleoenvironment /
- organic matter enrichment
点击查看大图
计量
- 文章访问数: 132
- PDF下载量: 21
- 被引次数: 0