原油热演化进程中烃类成熟度参数有效性探讨

Applicability of hydrocarbon-associated thermal maturity parameters as indicators of the thermal evolution of crude oil

原油中烃类生标化合物参数可以用于判识原油的成熟度,然而这些成熟度指标的有效性常受物源及热成熟阶段的影响。本研究主要对原油在热演化进程中成熟度参数的有效性进行探讨。在进入高成熟阶段(R_(o)>1.3%)后,常规原油成熟度参数Ts/(Ts+Tm)、C_(29)-20S/(20S+20R)和C_(29)-ββ/(ββ+αα)等,达到平衡不变或因化合物消耗殆尽难以准确测定,无法正确评价原油热演化特征。常用的甲基菲指标(MPI)因其具有分段性计算特征,实际应用时较难把握,容易导致误判。油藏进入高、过成熟演化阶段,指示芳构化程度的参数或一些热稳定性存在差异的芳烃异构化参数可以合理表征油藏热演化程度。实验结果表明,高、过成熟油藏中甲苯(Tol)与甲基环己烷(MCH)存在消长变化关系,2-甲基萘(2-MN)和1-甲基萘(1-MN)是热稳定性不同的异构体,Tol/(MCH+Tol)值和2-MN/(1-MN+2-MN)值与热演化成熟度参数Easy R_(o)之间存在良好的相关性,可以较好地应用于高成熟油藏成熟度的判识。

Traditional biomarker maturity parameters are very important in determining the thermal stage of crude oil reservoirs.However,some biomarker maturity indicators are constrained by their provenance and various thermal mature stages.In this study,we discuss the validity of biomarker maturity parameters in the thermal evolution of crude oil.The results showed that some conventional maturity parameters such as Ts/(Ts+Tm),C_(29)-20S/(20S+20R),and C_(29)-ββ/(ββ+αα)reached an equilibrium value without changing after the high maturity stage(such as R_(o)>1.3%),or broke down and thus cannot be used to properly evaluate the stage of thermal evolution of crude oil reservoirs.In addition,the commonly used methylphenanthrene index(MPI1)is difficult to properly apply in the oil reservoirs due to its piecewise evolution characteristics.As oil reservoirs entered the high mature stage,aromatization of hydrocarbon fluids became increasingly important,such that certain parameters associated with different thermal stabilities can be used to represent the thermal evolution index.The results of this study show that toluene(Tol)and methylcyclohexane(MCH)levels in oil may have a correlational relationship,thus the ratio of Tol/(MCH+Tol)can be applied to evaluate the thermal stage of oil reservoirs.Furthermore,2-methyl naphthalene(2-MN)and 1-methylnaphthalene(1-MN)have different thermal stabilities,and the ratios of 2-MN/(1-MN+2-MN)changed linearly with Easy R_(o).These parameters can be applied to the evaluation of mature oil reservoirs,particularly those in the high mature stage.