塔里木盆地台盆区原油甾、萜烷浓度与热稳定性

Concentrations and thermal stabilities of steranes and terpanes in crude oils from the cratonic regions of Tarim Basin

对塔里木盆地台盆区未遭受生物降解的138个原油样品进行甾、萜烷定量分析,展示原油甾、萜烷浓度随成熟度变化特征。C_(23)三环萜烷/(C_(23)三环萜烷+C_(30)藿烷)值与甾、萜烷浓度图版显示各类甾、萜烷具有不同的热稳定性。依据热稳定性的差异将甾、萜烷分为3类:第1类包括Tm、C_(29)藿烷和C_(30)藿烷等五环三萜烷,随成熟度增高,这类化合物浓度降低较快,具有相对较低的热稳定性;第2类既包括Ts、C_(29)Ts和C_(30)重排藿烷等五环三萜烷,也包括C_(27)和C_(29)规则甾烷各异构体,随成熟度增高,这类化合物浓度降低较慢,具有中等热稳定性;第3类包括C27重排甾烷、C_(21)甾烷和C_(23)三环萜烷,随成熟度增高,这类化合物浓度先增高、后降低,降低速率低于前2类化合物,表明其热稳定性相对较高。在常用的甾、萜烷成熟度指标中,Ts/(Ts+Tm)、C_(29)Ts/(C_(29)Ts+C_(29)藿烷)和C_(30)重排藿烷/(C_(30)重排藿烷+C_(30)藿烷)是基于第1类和第2类化合物之间的热稳定性差异;C_(27)重排甾烷/(C_(27)重排甾烷+C_(27)规则甾烷)和C_(21)/(C_(21)+∑C_(29))甾烷是基于第2类与第3类化合物之间的热稳定性差异;C_(23)三环萜烷/(C_(23)三环萜烷+C_(30)藿烷)则是基于第1类与第3类化合物之间的热稳定性差异,具有更好的应用效果。

We quantitatively analyzed steranes and terpanes in 138 non biodegraded crude oil samples in the platform basin of Tarim Basin to determine how the sterane and terpane concentrations varied as crude oils matured.Crossplots of the ratio of C_(23) tricyclic terpane/(C_(23) tricyclic terpane+C_(30) hopane)versus the concentrations of steranes and terpanes showed that different sterane and terpane compounds have different thermal stabilities.According to the thermal stability,sterane and terpene compounds were divided into three groups.The first group includes pentacyclic triterpenes such as Tm,C_(29) hopane,and C_(30) hopane.With increasing maturity,the concentrations of these compounds decreased rapidly and showed relatively low thermal stabilities.The second group includes some pentacyclic triterpanes such as Ts,C_(29)Ts,and C_(30) diahopane,as well as isomers of C_(27) and C_(29) regular steranes.With increasing maturity,the concentrations of these compounds decreased slowly and showed moderate thermal stability.The third group includes C_(27) rearranged steranes,C_(21) sterane,and C_(23) tricyclic terpane.With increasing maturity,the concentrations of compounds in the third group first increased and then decreased with lower decreasing rates and higher thermal stabilities than those in the other two groups.Among the routine maturity parameters of steranes and terpanes,the ratios of Ts/(Ts+Tm),C_(29)Ts/(C_(29)Ts+C_(29) hopane),and C_(30) diahopane/(C_(30) diahopane+C_(30) hopane)are based on differences in thermal stabilities between the first and second group compounds.The ratios of C_(27) rearranged sterane/(C_(27) rearranged steranes+C_(27) regular steranes),and C_(21)/(C_(21)+ΣC_(29))steranes were based on differences in thermal stabilities between the second and third group compounds.The ratio of C_(23) tricyclic terpane/(C_(23) tricyclic terpane+C_(30) hopane)was based on the difference in thermal stabilities between the first and third groups,which may be more effective.