【摘要】 通过对低成熟烃源岩中8α(H)-升补身烷和8β(H)-升补身烷以及2-乙基甲基四氢化萘和1-乙基甲基四氢化萘分布和组成特征的剖析,研究了8α(H)-升补身烷/8β(H)-升补身烷比值和1-乙基甲基四氢化萘/2-乙基甲基四氢化萘比值与镜质组反射率Ro之间的关系,发现在Ro<0.60%时,这两个比值变化幅度很大,表明这两个比值在低成熟阶段是衡量有机质热演化程度的有效指标。更多还原

【Abstract】 The study of thermal evolution of org anic matter in immature or low mature source rocks with vitrinite reflectance R o less than 0.60%is relatively diffic ult.The main reason is that at this stage,some molecular maturity parameters usually used su ch as sterane and terpane isomer rati os and methyl phenanthrene ratios are affected because of very limited varied range.In this paper,the Middle a nd Lower Jurassic immature source rocks from wells Lengke 1and Yu 25in t he Northwest Qaidam Basin are studie d.And 8α(H)-homodrimane,8β(H)-homodrimane,2-ethylmethyltetra hydronanphthalene and 1-ethylmeth yltetrahydronanphthalene are iden tified based on literature and the mass spec tra of compounds.And the correlatio n between the ratios of 8α(H)-homodrimane to 8β(H)-homodrimane and 1-ethylmethyltetrahydronanphthalene to 2-ethylmethyltetrahydro-nanphthalene and the vitrinite refl ectance R o values are analyzed.The results show that the distributions and the compositions of homodrimane isomers and monoaromatic homodrimane comp ounds are related to the relative thermal evolution of organic matter in immature or low mature source rock s.For example,the variation of vitrinite reflectance values R o in the source rocks from Well Yu 25is v ery limited,from 0.40%to 0.55%,showing the immaturity or low maturity of the source rocks.But the ratio v ariations of 8α(H)-homodrimane to 8β(H)-homodrimane and 2-ethylmethyltetrahydronanphthalene to 1-ethylmethyltetrahydronanphthalene are very great with increasing burial depth.Based on the correlation between the ratio s of 8α(H)-homodrimane to 8β(H)-homodrimane and 1-ethylmethyltetr ahydronanphthalene to 2-ethylmeth yltetrahydronanphthalene and the v itrinite reflectance R o values,it is found that when R o <0.60%,the two ratios vary greatly fr om 0.85,3.4to 0.35,0.50,respectively.But when R o >0.60%,the two ratios almost remain c onstant at about 0.05and 0.20,respectively.It means that they may be useful maturity indicators in determining the relative maturation of organic matter in immature or low mature sour ce rocks.更多还原