Compositional variabilities among crude oils from the southwestern part of the Qaidam Basin, NW China

A suite of crude oils have been analyzed by GC/MS in order to understand compositional heterogeneities in the oilfields located in the southwestern part of the Qaidam Basin, NW China. The oil samples investigated in this study can be grouped into two broad groups, A and B, based on the distributions of pentacyclic triterpanes. Group A oils predominately occurred in the northwestern part of the study area contain relatively high amounts of gammacerane and C₃₅ hopanes with the ratio of gammacerane to C₃₀ hopane (G/H) > 0.7 and the C₃₅/C₃₄ hopane ratio (C₃₅/C₃₄) > 1.2. In contrast, Group B oils mainly occurred in the southeastern part of the study area have relatively low values of G/H (~ < 0.7) and C₃₅/C₃₄ (< 1.2). Furthermore, Group A oils can be subdivided into three subgroups (A1, A2, and A3) by detailed investigation of molecular compositions of steranes, hopanes and aromatic sulfur compounds. Subgroup A1 oils, which mainly occurred in the westernmost corner, contain low amounts of dibenzothiophene (DBT) and methyldibenzothiophenes (MDBT) relative to C₃₀ hopane with the ratio of (DBT + MDBT)/C₃₀ hopane (DBT + MDBT/H) < ~ 0.25 and display high abundances of ααα20R C₂₈ sterane relative to C₂₉ compound with the C₂₈/C₂₉ sterane ratio > ~ 0.90. In contrast, subgroup A3 oils, which mainly occurred in depression areas, have relatively high values of (DBT + MDBT)/H (~ > 0.25) and relatively low ratios of C₂₈/C₂₉ sterane (~ < 0.90). Subgroup A2 oils, occurring in Gasikule and nearby oilfields, seem to have intermediate amounts of aromatic sulfur compounds and C₂₈ steranes relative to A1 and A3 oils, indicating a mixing signature of the two subgroups. The oil groups or subgroups revealed by the compositional heterogeneities and genetic affinities, as well as their regular occurrence in different oilfields, may indicate secondary petroleum systems existing within the Tertiary saline lacustrine petroleum in the southwestern Qaidam basin.     

煤样中单体显微组分的激光微裂解分析

镜质体和树脂体是煤中重要的有机显微组成,认识其化学组成及结构,对生烃潜力的评价具有重要意义。通过结合光学显微镜和优化的激光微裂解-色谱-质谱技术,分析了云南红河古近系煤样中单个镜质体和树脂体的激光微裂解产物。结果表明,单芳烃、双芳烃、二萜类化合物和正构烯烃/烷烃对等在两显微组分中均有检出,且芳烃化合物和二萜类化合物分布非常相似;丰富的降海松烷和扁枝烷指示了裸子植物,尤其是针叶树脂的贡献;脂肪烃以及藿类化合物的组成及分布不同,表明激光微裂解-色谱-质谱技术能够区分同一样品中不同显微组分的成烃差异,从而对有效生烃组分的判识提供重要的分子证据。除此之外,还探讨了与传统地球化学分析技术相比激光微裂解-色谱-质谱分析技术所具有的优势。     

Ribosylhopane,a Novel Bacterial Hopanoid,as Precursor of C35 Bacteriohopanepolyols in Streptomyces coelicolor A3(2)

Wild‐type Streptomyces coelicolor A3(2) produces aminobacteriohopanetriol as the only elongated C₃₅ hopanoid. The hopanoid phenotype of two mutants bearing a deletion of genes from a previously identified hopanoid biosynthesis gene cluster provides clues to the formation of C₃₅ bacteriohopanepolyols. orf14 encodes a putative nucleosidase; its deletion induces the accumulation of adenosylhopane as it cannot be converted into ribosylhopane. orf18 encodes a putative transaminase; its deletion results in the accumulation of adenosylhopane, ribosylhopane, and bacteriohopanetetrol. Ribosylhopane was postulated twenty years ago as a precursor for bacterial hopanoids but was never identified in a bacterium. Absence of the transaminase encoded by orf18 prevents the reductive amination of ribosylhopane into aminobacteriohopanetriol and induces its accumulation. Its reduction by an aldose‐reductase‐like enzyme produces bacteriohopanetetrol, which is normally not present in S. coelicolor.