塔里木盆地塔河油田原油地球化学特征的化学计量学分析及应用

Chemometric analysis and application research on geochemical characteristics of crude oil in Tahe Oilfield,Tarim Basin

塔里木盆地塔河油田由于存在多期次原油充注导致其成因至今无法得到很好地解释。应用地球化学手段对塔河油田原油地球化学特征进行综合研究,结果显示:塔河油田奥陶系原油沉积于海相沉积环境,处于成熟—过成熟阶段,正构烷烃分布较完整、具有UCM鼓包、普遍存在25-降藿烷、伽马蜡烷含量低,C_(29)藿烷丰度高、规则甾烷呈现C_(29)>C_(27)>C_(28)分布、规则甾烷αββ构型丰度高于ααα构型等特征,表明塔河油田原油遭受过较强程度的微生物降解作用,存在至少2个期次的原油充注。利用主成分分析(PCA)和层序聚类分析(HCA)方法对原油生物标志化合物指标进行分析,将塔河油田原油分为3类:I类原油具有三环萜烷/五环萜烷、Ts/17αC_(30)藿烷、重排甾烷/规则甾烷、C_(31)/C_(32)藿烷、C_(29)/C_(30)藿烷、C_(24)/C_(23)三环萜烷、C_(20+19)/C_(23+24)三环萜烷、Ts/Tm高,Ph/nC_(18)低,正构烷烃分布完整,呈现出多期充注特征,但主要表现出早期生物降解原油的特征,早期生物降解原油的贡献高于后期充注正常原油的贡献;Ⅱ类原油的nC_(21)^(-)/nC_(22)^(+)值最低,部分样品正构烷烃缺失,UCM鼓包明显,主要代表早期经历过强烈微生物降解的原油;Ⅲ类原油nC_(21)^(-)/nC_(22)^(+)、αβC_(31)-22S/(22S+22R)、C_(24)四环/(C_(24)四环+C_(26)三环)值最高,正构烷烃受热成熟度的影响最大,高碳数正构烷烃大量热裂解导致低碳数正构烷烃相对富集,代表混合原油但正常原油的贡献较大。

In this paper,the geochemical characteristics of crude oil in Tahe Oilfield,Tarim Basin are comprehensively studied by geochemical methods.The results show that the Ordovician crude oil in Tahe Oilfield was deposited in the marine sedimentary environment,which is in the mature to over-mature stage.The distribution of n-alkanes is relatively complete with UCM.The crude oils contain a certain abundance of 25-norhopane with low gamma wax contents.The regular sterane presents the distribution of C_(29)>C_(27)>C_(28),and αββ configuration abundance is higher than ααα.It shows that the crude oils in Tahe oilfield have suffered a strong degree of microbial degradation,and there are at least two stages of crude oil filling.Using the principal component analysis (PCA) and hierarchical cluster analysis (HCA) methods,the results show that the crude oil in Tahe Oilfield can be divided into three categories.Class I crude oils have high ratios of tricyclic/pentacyclic terpenoids,Ts/17αC30 hopane,rearranged sterane/regular sterane,C_(31)/C_(32)hopane,C_(29)/C_(30)hopane,C_(24)/C_(23)tricyclic terpenoids,C_(20+19)/C_(23+24) tricyclic terpenoids,Ts/Tm,and low Ph/nC18,showing the characteristics of early biodegradable crude oil with multi-stage filling.The contribution of early biodegradable crude oil is higher than that of later filling normal crude oil.Class Ⅱ crude oils have the lowest nC_(21)^(-)/nC_(22)^(+)with obvious UCM bulge,which mainly represents the crude oil that has experienced strong microbial degradation in the early stage.The stage.The nC_(21)^(-)/nC_(22)^(+),αβ C_(31)-22S/(22S+22R),C_(24)tetracyclic terpane/(C_(24)tetracyclic terpane+C_(26)tricyclic terpane) of class Ⅲ crude oils are the highest.The normal alkanes of class Ⅲ crude oils are most affected by thermal maturity,and the high-carbon normal alkanes are thermally cracked in large quantities,which represents mixed crude oil,but the contribution of normal crude oil is large.