柴达木盆地团鱼山地区浅湖油页岩特征、成因及成矿模式-以青柴地2井为例

Characteristics,Genesis and Metallogenic Model of Shallow-Lake Oil Shale in the Tuanyushan Area of Qaidam Basin:A Case Study of the Well QCD-2

我国陆相油页岩资源丰富,通常沉积于深湖-半深湖、湖沼以及浅湖环境,其中浅湖油页岩主要发育于柴达木盆地、老黑山盆地、黄县盆地等地区。为研究浅湖油页岩的特征和成因,分析其成矿模式,对柴达木盆地团鱼山地区的青柴地2井石门沟组含煤段浅湖油页岩样品分别开展了有机碳、热解、含油率、灰分、挥发分、密度、发热量、主微量元素、X衍射等测试分析。结果显示,研究区油页岩为中灰分、高挥发分、低密度、高发热量、低-中等含油率的油页岩。该油页岩的有机质丰度高,有机质类型为Ⅱ_(2)型,成熟度为未成熟。其矿物组成主要为粘土矿物和石英,组成元素以SiO_(2)、Al_(2)O_(3)和TFe_(2)O_(3)为主,具有P_(2)O_(5)、Co、Cu、Zn、Ga、Mo、Ba、Th、U等元素富集,SiO_(2)、TFe_(2)O_(3)、MgO、Na_(2)O、CaO、K_(2)O、TiO_(2)、MnO、Li、V、Cr、Ni、Rb、Sr、Zr等元素亏损的特点。油页岩沉积时具有温暖湿润的气候条件,微咸水-淡水的水体盐度和弱氧化-弱还原的保存条件。分析各环境因素显示,水体深度相对较大,水动力条件相对较强,盐度相对较高,保存条件较好,以及偏碱性的水体条件有利于有机质的富集和油页岩的形成,据此建立了研究区浅湖油页岩的形成模式。

China contains abundant continental oil shale resources,which were generally deposited in deep-semi deep lake,swamp,and shallowlake environments.Shallow-lake oil shales were mainly developed in the Qaidam Basin,Laoheishan Basin and Huangxian Basin.Aiming to determine the characteristics and genesis of shallow-lake oil shale and the metallogenic model,this work tested shallow-lake oil shale samples from the coalbearing section of the Shimengou Formation of well QCD-2 in the Tuanyushan area of Qaidam Basin,and analyzed the total organic carbon,rock eval,oil yield,ash content,volatile content,density,calorific value,major and trace elements,and X-ray diffraction.Results show that oil shale contains medium ash content,high volatile,low density,high calorific value,and low-medium oil yield.It includes high TOC,the organic matter is type Ⅱ_(2),and is immature.The minerals are dominated by clay minerals and quartz,and its constituent elements are mainly SiO_(2),Al_(2)O_(3) and TFe_(2)O_(3).It is characterized by the enrichment of P_(2)O_(5),Co,Cu,Zn,Ga,Mo,Ba,Th and U,and the depletion of SiO_(2),TFe_(2)O_(3),MgO,Na_(2)O,CaO,K_(2)O,TiO_(2),MnO,Li,V,Cr,Ni,Rb,Sr and Zr.During the deposition of the oil shale,the climate was warm and humid,the water salinity was brackish-freshwater,and the redox condition was weak oxidation-weak reduction.The analysis of various environmental factors indicates that relatively deep water,strong hydrodynamic conditions,relatively high salinity,better preservation,and alkaline water conditions are conducive to the enrichment of organic matter and the formation of oil shale.The formation model of the shallow-lake oil shale in the study area was also established.