东营凹陷南斜坡沙四下亚段—孔店组原油地球化学特征及成因分类

东营凹陷南斜坡沙四下亚段—孔店组为一套紫红色或红色碎屑岩沉积,本身不具备生烃能力,因此对该层段原油成因的研究具有重要意义。在系统分析17个油砂和5个原油样品的生物标志物组合特征的基础上,将该区原油划分为4种成因类型。Ⅰ类原油分布于平方王地区和博兴洼陷,Pr/Ph0.8,Ph/nC180.6,伽马蜡烷含量极低,4-甲基甾烷、重排甾烷含量相对高,Ts/Tm、藿烷/甾烷值相对高,可能来源于一套淡水湖相环境下形成的、富含粘土矿物的泥岩。Ⅱ类原油分布于纯化—乐安构造带、陈官庄构造带,Pr/Ph0.6,Ph/nC182,伽马蜡烷含量高,4-甲基甾烷、重排甾烷含量低,Ts/Tm和藿烷/甾烷值低,可能与一套盐湖相泥岩或灰质泥岩有成因关系。Ⅲ类原油分布于青城北缓坡构造带,检测出25-降藿烷系列,伽马蜡烷含量介于Ⅰ类和Ⅱ类之间,可能为早期充注的Ⅱ类原油遭受生物降解后和晚期充注的Ⅰ类原油形成的混源油,且以晚期充注为主。Ⅳ类原油分布于王家岗地区孔店组,具有C29甾烷绝对优势和高含量的伽马蜡烷,推断为Ⅱ类原油和一种来源于浅湖—沼泽相的原油形成的混源油。

Characteristics and Origin Classification of the Oils from the Lower Section of the 4th Member of Shahejie Formation and Kongdian Formation in the Southern Slope of Dongying Depression, Bohai Bay Basin

The lower section of the 4th member of Shahejie Formation and Kongdian Formation is a suite of purplish red and red clastic sediments in the southern slope of Dongying Depression which can not generate mass hydrocarbons.Therefore,it is significant to discuss the oil origin of the layers.Based on the biomarker characteristics analyses of the 17 oil sands and 5 crude oils,the origin of oils found in the study area was classified into four classes.Class-Ⅰ oil distributes in Pingfangwang area and Boxing subsag,being characterized by Pr/Ph>0.8,Ph/nC18<0.6,an extremely low content of gammacerane,a relatively high content of 4-methyl steranes and diasteranes and relatively high ratios of Ts/Tm and hopanes/steranes,which reflects the oil may come from a suite of mudstone rich in clay minerals deposited in the fresh water lacustrine environment.Class-Ⅱ oil distributes in Chunhua-Lean and Chenguanzhuang structural belt,characterized by Pr/Ph<0.6,Ph/nC18>2,a high content of gammacerane,a low content of 4-methyl steranes and diasteranes and relatively low ratios of Ts/Tm and hopanes/steranes,which indicates the oil sourced from a suite of mudstone or lime mudstone deposited in salt lacustrine environment.Class-Ⅲ oil distributes in the northern gentle slope structural belt of Qingcheng,characterized by the detection of 25-norhopanes and a middle content of gammacerane,which shows it is mixture of few biodegradated Class-Ⅱ oil charged in early stage and mass Class-Ⅰ oil charged in late stages.Class-Ⅳ oil distributes in Kongdian Formation of Wangjiagang area,characterized by an absolute predominant content of C29 steranes and a high content of gammacerane,which reveals the oil is mixture of Class-Ⅱ oil and the oil generated by shallow lake-swamp facies source rock.