甲基菲指数及甲基菲比值与有机质热演化关系——以柴达木盆地北缘地区为例

Relationship between methylphenanthrene index,methylphenanthrene ratio and organic thermal evolution: Take the northern margin of Qaidam Basin as an example

通过对柴达木盆地北缘地区未成熟—低成熟侏罗系烃源岩的热模拟实验研究,分析甲基菲的组成特征,建立两类Ⅱ型有机质（偏腐殖型、偏腐泥型）湖相烃源岩的甲基菲比值和甲基菲指数与镜质体反射率间的关系。研究表明,在有机质热演化的不同阶段,甲基菲指数与镜质体反射率间呈现出不同的关系式,同一甲基菲指数值将推算出2个不同的镜质体反射率,判断原油成熟度易出现偏差;而甲基菲比值与镜质体反射率间具有很好的线性正相关关系,Ro介于0.50%~1.80%时呈单调增加的趋势,相关系数高达0.90以上,在高成熟阶段两者间的关系也是正相关的,故利用甲基菲比值判断成熟度优于甲基菲指数。根据所建立的关系式对柴北缘各区原油的成熟度进行计算,所得结果与地质背景吻合度好,可信度较高。

Based on the study of thermal simulation of Jurassic immature and low mature source rock in the northern margin of Qaidam Basin,this paper builds up the relationships between methylphenanthrene ratio,methylphenanthrene index and vitrinite reflectance of two different types of Type-Ⅱ organic material lacustrine facies source rock（humic-prone and sapropel-prone organic material）.The result indicates that there are different relations between methylphenanthrene index and vitrinite reflectance in different stages of organic thermal evolution.The same methylphenanthrene index value corresponds with two different vitrinite reflectance ratios;it will show deviation when adjudging oil maturity;while the methylphenanthrene ratio and vitrinite reflectance ratio have good positive linear correlation.When Ro is between 0.50%-1.80%,the ratio will increase monotonously,and correlation coefficient will be over 0.90.The relation between them during high mature stage is also positive,thus methylphenanthrene ratio is superior to methylphenanthrene index to judge the oil maturity.Then the paper calculates the oil maturity in the northern margin of Qaidam Basin on the basis of the relationships.The result coincides well with the geological backgrounds and the confidence level is high.