Typification of oils in the Timan-Pechora province according to the composition of hydrocarbon biomarkers (steranes and terpanes)

Distinctive compositional features of cyclic saturated hydrocarbon biomarkers have been established in oils from the main petroliferous lithostratigraphic complexes of various structural zones in the Timan-Pechora petroliferous province (TPPP). Four geochemical families (types) of oils in TPPP are recognized based on the variations in the geochemical parameters of steranes and terpanes including sterane ratios C₂₇/C₂₉ and C₂₈/C₂₉, K¹ mat and K² mat, diasterane/regular sterane, pregnane (C_21–22)/sterane (C_21–22 + C_27–29), as well as terpane Ts/Tm parameters, adiantane C₂₉/hopane C₃₀, neoadiantane/adiantane, tryciclic terpane/pentacyclic terpane, hopane/sum of C₂₉ steranes, etc. The distribution of various types of oil in the sedimentary sequence of TPPP makes it possible to infer source rocks for each of the four selected types.     

An assessment of paleodepositional environment and maturity of organic matter in sediments of the Setap Shale and Belait formations in West Sabah,East Malaysia by organic geochemical methods

The black shale samples collected from two Neogene formations in the Klias Peninsula area, West Sabah, have been assessed and characterized in details by gas chromatography, gas chromatography-mass spectrometry and a variety of organic geochemical parameters. The aims of this study are to describe the characteristics of organic matter of these sediments in terms of source/type of the organic matter, assess its thermal maturity and paleoenvironment of deposition, based primarily on biomarker distributions. The results of both formations do not reveal significant differences within the rock extracts. The gas chromatograms of the saturated hydrocarbon fractions of the Setap Shale and the Belait formations displayed monomodal n-alkane distributions and nearly identical regular sterane compositions with a predominance of C₂₇ regular steranes. These are consistent with open marine depositional environments dominated by marine biological matter. Another related feature of these rock extracts is the presence of a high relative abundance of gammacerane, indicating anoxic marine hypersaline source depositional environment. The relatively high abundance of common land plant-derived biomarkers, such as bicadinanes and oleananes, is a clear indication of a major terrigenous input to the source of the extractable organic matter. The predominance of oleanane biomarkers in both formations is indicative of angiospermis input and Tertiary source rocks. The high C₂₉/C₃₀ hopane ratios, moderate development of C₃₃–C₃₅ hopanes, high abundance of tricyclic terpanes and a slight predominance of C₂₇ regular sterane over C₂₈ and C₂₉ steranes are characteristic features tending to suggest a significant marine influence on these source rocks, thereby suggesting a mixed source input. The 22S/(22S+22R)C₃₂ hopane ratio has reached equilibrium, and this is supported by the high maturity level as indicated by the 22S/22SC_31–33 extended hopane ratios and 20S/(20S+20R)C₂₉ regular steranes ratios.     

Geochemistry and possible origin of petroleum in Palaeozoic reservoirs from Halahatang Depression

The Halahatang Depression in the Tabei Uplift of the Tarim basin is an active exploration area because it has substantial reservoir potential and contains or is near to many commercial oil fields. Geochemical analysis indicates that Halahatang oils were derived from marine carbonate source rocks deposited under anoxic reducing conditions. The maturities for Halahatang oils are corresponding to the peak of the oil window and slightly higher than the neighboring Tahe oils. The Halahatang oils feature low Pr/Ph, C₂₁/C₂₃ tricyclic terpane and, C₂₈/C₂₉ sterane ratios, high C₂₉/C₃₀ hopane and C₃₅/C₃₄ hopane ratios, a “V” shape in the distribution of C₂₇–C₂₈–C₂₉ steranes and light carbon isotope ratios, similar to the Tahe oils and correlate well with the Middle-Upper Ordovician source rock. However, some source-related biomarker parameters imply a more reducing source organofacies with more zooplanktonic contribution than that for the Tahe oils.     

Petroleum geochemistry of the Potwar Basin, Pakistan: 1. Oil-oil correlation using biomarkers, δC and δD

Geochemical characterisation of 18 crude oils from the Potwar Basin (Upper Indus), Pakistan is carried out in this study. Their relative thermal maturities, environment of deposition, source of organic matter (OM) and the extent of biodegradation based on the hydrocarbon (HC) distributions are investigated. A detailed oil-oil correlation of the area is established. Gas chromatography-mass spectrometry (GC-MS) analyses and bulk stable carbon and hydrogen isotopic compositions of saturated and aromatic HC fractions reveals three compositional groups of oils. Most of the oils from the basin are typically generated from shallow marine source rocks. However, group A contains terrigenous OM deposited under highly oxic/fluvio-deltaic conditions reflected by high pristane/phytane (Pr/Ph), C₃₀ diahopane/C₂₉Ts, diahopane/hopane and diasterane/sterane ratios and low dibenzothiophene (DBT)/phenanthrene (P) ratios. The abundance of C₁₉-tricyclic and C₂₄-tetracyclic terpanes are consistent with a predominant terrigenous OM source for group A. Saturated HC biomarker parameters from the rest of the oils show a predominant marine origin, however groups B and C are clearly separated by bulk δ¹³C and δD and the distributions of the saturated HC fractions supporting variations in source and environment of deposition of their respective source rocks. Moreover, various saturated HC biomarker ratios such as steranes/hopanes, diasteranes/steranes, C₂₃-tricyclic/C₃₀ hopane, C₂₈-tricyclic/C₃₀ hopane, total tricyclic terpanes/hopanes and C₃₁(R + S)/C₃₀ hopane show that two different groups are present. These biomarker ratios show that group B oils are generated from clastic-rich source rocks deposited under more suboxic depositional environments compared to group C oils. Group C oils show a relatively higher input of algal mixed with terrigenous OM, supported by the abundance of extended tricyclic terpanes (up to C₄₁₊) and steranes.Biomarker thermal maturity parameters mostly reached to their equilibrium values indicating that the source rocks for Potwar Basin oils must have reached the early to peak oil generation window, while aromatic HC parameters suggest up to late oil window thermal maturity. The extent of biodegradation of the Potwar Basin oils is determined using various saturated HC parameters and variations in bulk properties such as API gravity. Groups A and C oils are not biodegraded and show mature HC profiles, while some of the oils from group B show minor levels of biodegradation consistent with high Pr/n-C₁₇, Ph/n-C₁₈ and low API gravities.     

小太平山油砂油地球化学及生物降解特征

采用小太平山同一层位不同深度且连续的油砂样品,对油砂油的地球化学及生物降解特征进行分析。小太平山油砂油在生物降解作用下产生了丰富的25-降霍烷,常规藿烷和甾烷也发生了一系列变化。由于分子结构和稳定性不同,抗降解能力不同,C_(21)/C_(23)三环萜烷、伽马蜡烷/C_(30)藿烷、Ts/Tm、C_(30)重排藿烷/C_(30)藿烷值、αααC_(27)R/αααC_(29)R、C_(28)αααR/C_(29)αααR、C_(29)ααα20R/αββ20S、C_(29)ααα20R/αββ20R、C_(27)重排甾烷/(规则甾烷+重排甾烷)、常规藿烷异构体降解为25-降霍烷的比例,均反映出油砂油的生物降解程度随深度的增加而增大。小太平山油砂油随含水饱和度的增加降解程度增大,证实地层水有利于细菌类微生物的迁移、营养物质的传递,促进原油的生物降解及25-降霍烷的产生。     

Oil geochemistry derived from the Qinjiatun–Qikeshu oilfields: insight from light hydrocarbons

A suite of 27 oils from the Qinjiatun–Qikeshu oilfields in the Lishu Fault Depression of the Songliao Basin was analyzed using whole oil gas chromatography. In combination with the relative distribution of C₂₇, C₂₈, and C₂₉ regular steranes, detailed geochemical analyses of light hydrocarbons in oil samples revealed crude oils characterized by the dual input of lower aquatic organisms and higher terrestrial plants. Several light hydrocarbon indicators suggest that the liquid hydrocarbons have maturities equivalent to vitrinite reflectances of around 0.78%–0.93%. This is consistent with the maturity determination of steranes C₂₉ 20S/(20S + 20R) and C₂₉ ααβ/(ααα + αββ). Crude oils derived from the two distinct oilfields likely both have source rocks deposited in a lacustrine environment based on light hydrocarbon parameters and on higher molecular weight hydrocarbon parameters. The results show that light hydrocarbon data in crude oils can provide important information for understanding the geochemical characteristics of the Qinjiatun–Qikeshu oils during geologic evolution.     

柴达木盆地东坪地区一类新的原油及其地球化学特征

各类生物标志物的组成特征表明:柴达木盆地北缘的冷湖油田原油具有姥植比高（Pr/Ph>2.0）,重排甾烷（C₂₇重排甾烷/规则甾烷=0.5~0.7）、重排藿烷（diaC₃₀H/C₃₀H=0.2~0.4）和新藿烷（C₂₉Ts/C₂₉H=0.4~0.7）含量中等,伽马蜡烷含量低（伽马蜡烷指数<0.05）的特征,它们源于该地区发育的下侏罗统淡水湖沼相烃源岩;而柴西北区咸水湖相原油的姥植比低（Pr/Ph<0.8）,重排甾烷（C₂₇重排甾烷/规则甾烷<0.1）、重排藿烷（diaC₃₀H/C₃₀H<0.05）和新藿烷（C₂₉Ts/C₂₉H=0.2~0.4）含量低和伽马蜡烷含量高（伽马蜡烷指数=0.4~0.8）,这一系列特征与柴西地区发育的古近系-新近系咸水湖相烃源岩一致。但是,东坪地区原油呈现完全不同的生物标志物组合,主要表现为丰富的伽马蜡烷（伽马蜡烷指数=1.2~3.0）与高含量的新藿烷（C₂₉Ts/C₂₉H>1.5）、重排藿烷（diaC₃₀H/C₃₀H>0.7）和重排甾烷（C₂₇重排甾烷/规则甾烷>0.4）并存,这与地质样品中伽马蜡烷和重排类标志物的分布特征相矛盾,因为依据现有的认识无法解释这一特殊地球化学现象。生物标志物组成特征表明东坪地区原油所具有的特殊生物标志物组合并非源于不同类型原油之间的混合,而是一种客观存在,尽管其确切的地球化学意义和形成条件目前并不清楚。由此可见,东坪地区原油为柴达木盆地一个新的原油类型,推测其烃源岩可能形成于偏酸性的咸水环境。     

Sterane isomerisation and moretane/hopane ratios in crude oils derived from Tertiary source rocks

The extent of sterane isomerisation reactions and the moretane/hopane ratios of 234 crude oils, taken world wide, from a wide variety of source rocks of differing geological ages, have been measured.This data indicates that in 78 crude oils derived from Tertiary source rocks, sterane isomerisation reactions as determined by the 20S/(20S + 20R) ration of the C₂₉ 5α(H), 14α(H), 17α(H) normal-steranes and the C₂₉ iso/(iso + normal) ratio [iso = 5α (H), 14β(H), 17β(H)] are mainly incomplete and sometimes considerably so. In addition, the same crude oils have 17β(H), 21α(H)-moretane/17α(H), 21β(H)-hopane ratios which are significantly greater (predominantly in the range 0.10–0.30) than those of crude oils derived from older, mature source rocks (mainly less than 0.1).This data, for crude oils, lends support to the hypothesis, proposed by Mackenzie and McKenzie (1983) for source rock extracts, that the time/temperature constraints of sterane isomerisation reactions are such that the time available for isomerisation in Tertiary sediments is generally insufficient, despite generation of crude oil at relatively high temperatures.An alternative hypothesis is that the incomplete sterane isomerisation of Tertiary crude oils may be due to generation of these crude oils from their deltaic, land plant-containing source rocks under low heating conditions.A third hypothesis proposes that the Tertiary crude oils may have picked up the incompletely isomerised steranes from immature sediments during migration. Although possible in particular instances, such a mechanism does not appear to be generally applicable since, in that case, the phenomenon would then appear to be restricted to the Tertiary.The higher moretane/hopane ratios of the Tertiary crude oils could suggest that constraints, similar to those applying in sterane isomerisation, also operate in the conversion of moretane to 17α(H)-hopane.     

四川南桐地区二叠系龙潭煤层生物标记物及其地质意义

四川南桐地区二叠系龙潭煤层具有良好的生油潜力。其生物标记物包括正构和异构烷烃,类异戊二烯烷烃,倍半萜烷,二萜烷,三环萜烷,藿烷,一种未知结构的五环三萜烷(C₃₀),甾烷,4-甲基甾烷等。煤层生物标记物特征表明在其形成过程中有藻类和细菌等微生物物质的加入。     

鄂尔多斯盆地西南缘奥陶系泥页岩与碳酸盐岩生物标志物特征对比

通过采集鄂尔多斯盆地西南缘4个剖面奥陶系马家沟群碳酸盐岩和平凉组泥页岩样品,对其中可溶有机质饱和烃与芳烃组分进行GC-MS分析,对比研究了马家沟群碳酸盐岩和平凉组泥页岩生物标志化合物特征。结果表明,马家沟群与平凉组正构烷烃分布形式及峰型特征、生物标志化合物参数Pr/Ph、伽马蜡烷/C₃₀-αβ藿烷、C_20-29三环萜烷/(C_20-29三环萜烷+C_27-35藿烷),以及甲基菲指数(MPI)均存在明显差异,这些差异反映了其沉积环境与成熟度的不同,对于马家沟群与平凉组来源油的识别具有参考价值。马家沟群正构烷烃分布形式与甾/藿比值以及C₂₈/C₂₉ααα20R甾烷比值之间的对应关系,反映了母质输入的细微差别。Ts/(Ts+Tm)与伽马蜡烷/C₃₀-αβ藿烷比值之间的关系,C₂₉甾烷αββ/(αββ+ααα)比值变化与重排藿烷与重排甾烷丰度的关系,反映上述成熟度参数明显受沉积环境影响。     

Identification of C24 and C25 lanostanes in Tertiary sulfur rich crude oils from the Jinxian Sag, Bohai Bay Basin, Northern China

Unusual short chain lanostanes (C₂₄ and C₂₅) and C₃₀ lanostane were identified in sulfur rich crude oils from the Jinxian Sag, Bohai Bay Basin, northern China. Besides the regular steranes (C_27-30), a series of 4-methyl steranes (C₂₂₋₂₃, C₂₇₋₃₀), 4,4-dimethyl steranes (C₂₂₋₂₄, C₂₈₋₃₀), short chain steranes (C₂₃₋₂₆), abundant pregnanes (C₂₁₋₂₂) and androstanes (C₁₉₋₂₀), together with sulfur containing steroids (20-thienylpregnanes and thienylandrostanes) were detected in the aliphatic and branched-cyclic hydrocarbon fraction of these crude oils. A literature survey of some long chain sterane analogues (e.g., A-nor-steranes, norcholestanes, C₃₀ steranes, lanostanes) and pregnanes seems to point to a sponge and/or dinoflagellate source. 4-Methyl, 4,4-dimethyl steroids and lanosterols (4,4,14-trimethyl steroids as the basic skeleton of lanostanes) can be derived from methanotrophic bacteria. Thus, a biological origin from a prokaryotic methylotroph can be used to explain the common source of abundant short chain steranes (C_23-26), 4-methyl (C_22-23) and 4,4-dimethyl steranes (C_22-24), as well as lanostanes (C_24-25 and C₃₀ analogues) in our oil samples. Generally, the steroids appear to have been extensively sulfurized with sulfur substitution at the C-22 position in the side chain during the early stage of diagenesis, which was readily subject to attack by bacterial degradation (enzymatic cleavage) and/or abiotic oxidation. As a consequence, short chain sterane analogues (e.g., abundant pregnanes and androstanes in this study) and short chain lanostanes (C₂₄−C₂₅) might later be released through cleavage of weak C-S bonds at the C-22 carbon in the sulfurized steroids and lanostane sulfides. Finally, the formation of the short chain C₂₄−C₂₅ lanostanes and distinctive occurrence of short chain steranes in this study can be well explained by microbial biodegradation of sulfurized lanostanoids and steroids in the reservoir.     

Dinosterane and other steroidal hydrocarbons of dinoflagellate origin in sediments and petroleum

The steroidal alkanes of a selection of sediments and oils have been examined by GC-MS with multiple metastable reaction monitoring. Specific 4-methyl sterane isomers have been identified by comparison with isomers synthesized from sterols isolated from dinoflagellates. An immature marine oil shale and two mature marine oils of Triassic to early Cretaceous age contained high concentrations of C₃₀ steranes comprising desmethyl, 24-ethyl-4α-methylcholestane and 4α,23,24-trimethylcholestane (dinosterane) isomers. An immature non-marine oil shale and two non-marine oils of Cretaceous to Eocene age contained stereoisomers of 24-ethyl-4α-methylcholestane as the dominant C₃₀ steranes. Reaction monitoring analyses in GC-MS are particularly suited to unravelling complex distributions of homologous and stereoisomeric steroids encountered in oils and their source rocks.     

Molecular correlation of crude oils and oil components from reservoir rocks in the Tazhong and Tabei uplifts of the Tarim Basin, China

Molecular data from a large set of source rock, crude oil and oil-containing reservoir rock samples from the Tarim Basin demonstrate multiple sources for the marine oils in the studied areas of this basin. Based on gammacerane/C₃₁ hopane and C₂₈/(C₂₇ + C₂₈ + C₂₉) sterane ratios, three of the fifteen crude oils from the Tazhong Uplift correlate with Cambrian-Lower Ordovician source rocks, while the other crude oils from the Tazhong Uplift and all 39 crude oils from the Tahe oilfield in the Tabei Uplift correlate with Middle-Upper Ordovician source rocks. These two ratios further demonstrate that most of the free oils and nearly all of the adsorbed and inclusion oils in oil-containing reservoir rocks from the Tazhong Uplift correlate with Cambrian-Lower Ordovician source rocks, while the free and inclusion oils in oil-containing carbonates from the Tahe oilfield correlate mainly with Middle-Upper Ordovician source rocks. This result suggests that crude oils in the Tazhong Uplift are partly derived from the Cambrian-Lower Ordovician source rocks while those in the Ordovician carbonate reservoirs of Tahe oilfield are overwhelmingly derived from the Middle-Upper Ordovician source rocks.The scatter of C₂₃ tricyclic terpane/(C₂₃ tricyclic terpane + C₃₀ 17α,21β(H)-hopane) and C₂₁/(C₂₁ + ΣC₂₉) sterane ratios for the free and inclusion oils from oil-containing carbonates in the Tahe oilfield possibly reflects the subtle organofacies variations in the source rocks, implying that the Ordovician reservoirs in this oilfield are near the major source kitchen. In contrast, the close and positive relationship between these two ratios for oil components in the oil-containing reservoir rocks from the Tazhong Uplift implies that they are far from the major source kitchen.     

Petroleum geochemistry of the Potwar Basin,Pakistan: II – Oil classification based on heterocyclic and polycyclic aromatic hydrocarbons

In a previous study, oils in the Potwar Basin (Upper Indus) of Pakistan were correlated based on the dissimilarity of source and depositional environment of organic matter (OM) using biomarkers and bulk stable isotopes. This study is aimed at supporting the classification of Potwar Basin oils into three groups (A, B and C) using the distribution of alkylnaphthalenes, alkylphenanthrenes, alkyldibenzothiophenes, alkyldibenzofurans, alkylfluorenes, alkylbiphenyls, triaromatic steroids, methyl triaromatic steroids, retene, methyl retenes and cadalene. The higher relative abundance of specific methyl isomers of naphthalene and phenanthrene and the presence of diagnostic aromatic biomarkers clearly indicate the terrigenous and oxic depositional environment of OM for group A oil. Group B and C oils are of marine origin and the aforementioned heterocyclic and polycyclic aromatic hydrocarbons (HCs) differentiate them clearly into two different groups. The relative percentages of heterocyclic aromatic HCs reveal that the distribution of these compounds is controlled by the depositional environment of the OM. Sulfur-containing heterocyclic aromatic HCs are higher in crude oils generated from source rocks deposited in suboxic depositional environments, while oxygen-containing heterocyclic aromatic HCs in combination with alkylfluorenes are higher in marine oxic and deltaic oils. Biomarker and aromatic HC parameters do not indicate significant differences in the thermal maturity of Potwar Basin oils. Triaromatic and methyl triaromatic steroids support the division of Potwar Basin oils into the three groups and their relative abundances are related to source OM rather than thermal maturity. Significantly higher amounts of C₂₀ and C₂₁ triaromtic steroids and the presence or absence of long chain triaromatic steroids (C₂₅, C₂₆, C₂₇, and C₂₈) indicates that these compounds are probably formed from different biological precursors in each group. Different isomers of methyl substituted triaromatic steroids are present only for short chain compounds (C₂₀–C₂₂) and the origin of these compounds may be short chain methyl steranes from unknown biological precursors.     

泌阳凹陷第三系湖相泥质白云岩中特殊甾烷化合物分布特征及地球化学意义

在研究羊毛甾烷的基础上，又从泌阳凹陷第三系湖相泥质白云岩地层中检测出了其他系列的特殊甾烷化合物，如３β－乙基甾烷（Ｃ（２９）－Ｃ（３１）），３β－正丙基甾烷（Ｃ（３０）－Ｃ（３２））和３β－丁基甾烷（Ｃ（３１）－Ｃ（３３））和甲藻甾烷等。这些特殊甾烷集中出现的情况曾未报道过。除母源输入具有特殊组合外，水体较高盐度和强还原环境可能是这些化合物得以保存的重要原因。     

Characteristics of biomarkers in source rocks of the Ganquan Formation in the Dahulishan region, Ejina Banner

Based on gas chromatography and gas chromatography mass spectrometry techniques, the authors examined biomarker characteristics of the Ganquan Formation source rocks in the area of Dahulishan, Ejina, and analyzed the information and petroleum geological significance that were indicated by the source of organic matter, sedimentary environment and maturity and so on. Gas chromatography peak of saturated hydrocarbons from the Ganquan Formation source rocks showed "the former peak" of the single peak distribution, the main peak of carbon being C18 , indicating the main sources of organic matter with marine organic matter. Pr/Ph ranges from 0.3 to 0.6, indicating a strongly reducing sedimentary environment. Biomarker assemblages of the Ganquan Formation source rocks are abundant in tricyclic terpane with long side chains, with a high level of gammacerane, showing dominant distribution of C27 sterane. High contents of gammacerane in organic matter show organic facies of source rocks in the saltwater sedimentary environment. That average hopane/sterane ratio is 0.59, showing that algae have made more contributions to organic matter than bacteria. And the high level of C27 steranes shows that algae are the main source of hydrocarbon precursors. The Ganquan Formation’s methylphenanthrene index, which is an effective molecular parameter index to measure thermal evolution of organic matter, ranges from 0.35 to 0.50, and the conversion of vitrinite reflectance Rc from it is within the range of 2.00-2.09, indicating that the Ganquan Formation source rocks are in the over-mature stage of thermal evolution.     

塔河油田原油甾藿烷系列化合物地球化学再认识

生物标志化合物是油气油源、成熟度、运移等领域研究中的一项得力工具。运用生物标志物色谱质谱技术，对比研究了塔河油田各油区原油生物标志化合物中甾、藿烷系列化合物特征。研究表明，塔河油田为一由晚期成熟高、轻微改造的原油与早期成熟度低、遭受较强降解原油混合而成的复合油藏，该油藏各区原油C27—C29甾烷同系物以及C27—C29重排甾烷特征反映出该区不同成熟度原油来自同一母源，原油Ts/(Tm+Ts)、重排甾烷/规则甾烷和ββ/(ββ+αα) C29比值关系立体图指示出原油的充注方向，印证了“塔河地区的油气主要来自于南部的满加尔坳陷”这一论点。     

Geochemical characteristics of Lower Permian coal-measure source rocks in Northeast Ordos Basin

General characteristics and biomarker distributions of Lower Permian coal-measure source rocks in northeastern Ordos Bsain have been analyzed in this paper. The results show that the source rocks are type III kerogen, thermally mature, with high content of total organic carbon. The extracts of the source rock samples with different lithologies from Well Su 27 feature high Pr/Ph ratios, high C19TT and C24Te, high rearranged hopanes, a predominance of C29 sterane in regular steranes, and the absence of C30 4-methylsteranes. These data suggest that the source rocks were deposited in suboxic to oxic conditions with dominantly terrigenous higher plant input. In contrast, the source rocks from wells Shuang 1 and Yu 20, are characterized by low Pr/Ph ratios, low C19TT and C24Te, high C23TT, similar content of C27 sterane and C29 sterane, and the presence of C30 4-methylsteranes, showing that the source rocks were deposited in reducing environment with algae and/or microorganisms and terrigenous higher plant input.     

民和盆地中侏罗统煤-油页岩层系生油特征

本文简要论述了民和盆地中侏罗统含煤及油页岩层系的生油特征，探讨了盆地独特的石油地质和地球化学条件。原油主要地化特征为:Ｐｒ/Ｐｈ比值偏高（２.６５-３.１５）、甾烷/藿烷比值极低（０.０３）、Ｃ_２７甾烷较丰富、Ｔｓ/Ｔｍ＞１低硫芴/氧芴比值、较高含量的Ｃ_２９降新藿烷及重排藿烷类化合物及相对丰富的长链联苯及烷基四氢萘系列化合物。中侏罗统煤－泥页岩层系含生油潜力明显不同的多类型油页岩，多数油页岩属由藻类和陆生高等植物母质组成的混合型有机质，沉积环境为淡水－微咸水弱氧化条件，其地化特征也表现为高Ｐｒ/Ｐｈ比值（平均为１。９８），低甾烷/藿烷及低硫芴/氧芴比值等特征。某些油页岩富含Ｃ_２９降新藿烷及重排藿烷系列化合物，它们应为主力源岩。油页岩多含再沉积型或沉积改造型有机质。异常地热作用对源岩演化及原油地化特征有重要影响。     

柴达木盆地北缘冷湖地区原油对比

借助色谱质谱测试,对柴达木盆地北缘冷湖地区冷湖三、四、五号构造上22 个原油样品的生物标志化合物组成进行了系统分析。根据萜烷和甾烷相对含量的不同,将该区原油分成为3 类,即低熟单源型原油、成熟混源型原油和高熟混源型原油。对比研究表明,冷湖三号、四号构造原油链烷烃表现为nC20 前低分子量优势,五号构造原油则表现为nC21 后高分子量优势,从三号至五号,原油中四环萜烷相对含量逐渐变小,而重排藿烷、重排甾烷相对含量依次增加,说明母源类型依次变差,而成熟度则依次变高。