塔里木盆地部分来自寒武系烃源岩贡献的原油富集~(13)C同位素的成因探讨

<正>近年来发现塔里木盆地典型来自于寒武系-下奥陶统烃源岩的原油具有富集13C的特征,其稳定碳同位素比值基本上集中在-28‰左右。比如:塔东2井寒武系储层中的原油明显具有寒武系-下奥陶统烃源岩成因原油的生标分布特征,被认为是寒武系自生自储的一个古油藏,其全油稳定碳同位素比值为-28.283‰,但相应的烃源岩干酪根同位素比值在-31‰左右;塔中62井志留系储层的原油被认为是一典型来自于寒武系烃源岩的透镜体油藏,其全油稳定碳同位素比值为-28.606‰;另外被认为来自于寒武系-     

四川盆地磨溪地区龙王庙组储层沥青的地球化学特征及其意义

根据储层中沥青的产状、元素组成、固体碳同位素、饱和烃色谱、生物标志化合物以及芳烃色谱-质谱等,对磨溪地区龙王庙组储层固体沥青的地球化学特征、成因及来源进行了剖析。研究结果表明,其总体上具有低H/C原子比值、高反射率的特征,是古油藏原油经裂解形成的残留物。储层沥青的正构烷烃分布较为完整,碳数在C₁₆-C₃₁范围,没有受到明显的生物降解作用。其可能的烃源岩发育于还原环境,有机质来源于低等水生生物,为海相泥页岩。固体沥青碳同位素值介于-33.1‰~-35.4‰之间,与下寒武统烃源岩干酪根碳同位素具有很好的可比性,同时,其生物标志化合物组成也与下寒武统烃源岩相似,表明其烃源来自于下寒武统筇竹寺组。     

塔中隆起原油特征与成因类型

塔里木盆地塔中隆起油气性质多样、分布与成因复杂, 为揭示油气的特征与成因, 对塔中及外围104个原油样品进行了精细地球化学研究.依据单体烃碳同位素、特征生物标志物分析, 将塔中原油分为4种类型: (1) 寒武系成因原油, 具有较重正构烷烃单体烃碳同位素(-29.6‰~-29.1‰)、甲藻甾烷较发育及C₂₇、C₂₈、C₂₉规则甾烷呈反“L”型或线型分布等特征; (2) 中、上奥陶统成因原油, 具有较轻的正构烷烃单体烃同位素(-34‰~-35.6‰)、甲藻甾烷等不太发育与C₂₇、C₂₈、C₂₉规则甾烷呈“V”型分布等特征; (3) 富含含硫芳烃-二苯并噻吩原油, 主要分布于塔中4井区; (4) 混源油, 单体烃碳同位素特征界于Ⅰ、Ⅱ类原油之间, 是塔中最为主要的原油类型.油-油对比与油气性质分析表明, 塔中地区至少有两套主力烃源岩供烃.塔中部分原油生物标志物显示寒武系-下奥陶统成因特征, 而单体烃碳同位素却与中上奥陶统成因原油更为接近, 这种不同馏分的不一致现象系不同成因原油混源的结果, 反映单一应用生物标志物指标有其局限性.塔中油气性质具有分带、分块、分层特征, 反映叠合盆地多源、多期成藏、储层非均质性等多种特性.      

凯里-麻江地区油苗与固体沥青的油源分析

对黔南坳陷典型古油藏、残余油气藏的精细解剖对南方海相碳酸盐岩层系油气勘探研究具有重要意义。本文运用碳同位素、饱和烃色谱、饱和烃色质及芳烃色质等技术,对黔东南地区二叠系—寒武系油苗与固体沥青进行了地球化学特征研究和油源分析。研究表明,凯里地区虎庄47井原油、洛棉志留系砂岩油苗和麻江地区奥陶系红花园组固体沥青三者同源,主要来自下寒武统牛蹄塘组的优质烃源岩。而麻江地区早二叠世茅口组油苗与虎庄47井原油明显不同,主要源于下二叠统栖霞组的优质烃源岩。     

塔里木盆地海相油气源与混源成藏模式

塔里木盆地油气源长期争论不休.采用单体烃同位素、包裹体成分与年代指示生物标志物等途径, 对塔里木盆地塔中、轮南典型油气藏进行了油气成因与混源成藏模式的研究.结果表明, 塔中、轮南绝大部分原油生物标志物与中上奥陶统烃源岩相似, 仅少部分原油显现与寒武系—下奥陶统烃源岩相近的特征, 但正构烷烃单体烃碳同位素分析表明, 原油绝大部分实质仍为混源油.塔中包裹烃成分分析进一步证实了原油的混源特性.利用同位素进行的混源定量结果表明, 塔中原油中寒武系—下奥陶统成因原油的混入量约为11%~100%(均值45%); 轮南地区约为11%~70%(均值36%), 表明寒武系—下奥陶统、中上奥陶统均为塔里木盆地的主力烃源岩.油气运移地化指标与地质条件的综合研究认为, 塔中地区断层是油气运移的重要通道, 塔中I号断层与斜交的走滑断层的交汇点是油气的主要注入点; 轮南地区侧向运移特征较明显.研究区存在调整型、多期充注型与原生型多种混源成藏模式.塔里木海相油气的普遍混源表明深层仍有油气勘探潜能.揭示海相混源油气成藏机制是指导塔里木海相油气勘探的关键.      

塔中古生界储层中流体包裹体成分分析及其意义

对塔中地区30个储层包裹体样品进行了MCI(包裹体成分)与单体烃同位素分析.观察到包裹油与储层油既有区别又有联系.共有6个包裹体特别是下奥陶统样品显示C28-甾烷丰度相对较高、甾烷异构化程度相对较低、低分子量甾萜类化合物丰度相对较高等寒武系的成因特征,指示寒武系源岩对塔中地区有成烃贡献.多数分析包裹油显示中上奥陶统成因生物标志物特征,以及介于寒武系与中上奥陶统成因原油之间的单体正构烷烃同位素特征,个别包裹油显示与中上奥陶统完全一致的单体同位素与生物标志物特征,指示中上奥陶统对塔中地区也具有成烃贡献.塔中部分包裹油与储层油间、包裹油间显著的地球化学性质差异,指示该区具明显的多期成藏特征.塔中储层包裹体成分分析可有效地用于识别端员油、多期充注与混源聚集、恢复生物降解、气侵等次生改造原油面貌.流体包裹体成分分析对于叠合盆地的油气成因与成藏过程研究有重要意义.     

塔里木盆地塔东2井原油成因分析

塔东2井原油为高密度、粘度大,δ13C相对较重的稠油.原油中轻烃、环状萜类、甾烷及芳香甾烷组成与分布均具有海相原油的特点.具有时代意义生物标志物的油源对比结果表明,该原油来源于寒武系烃源岩,具有自生自储特点.高反射率热解沥青的存在、芳烃馏分中高含量的多元稠环芳烃及正构烷烃碳同位素相对较重的特点,表明原油在成藏后经历了短期高温热事件的影响.     

塔里木盆地塔东2井原油成因分析

塔东2井原油为高密度、粘度大，δ^13C相对较重的稠油。原油中轻烃、环状萜类、甾烷及芳香甾烷组成与分布均具有海相原油的特点。具有时代意义生物标志物的油源对比结果表明，该原油来源于寒武系烃源岩，具有自生自储特点。高反射率热解沥青的存在、芳烃馏分中高含量的多元稠环芳烃及正构烷烃碳同位素相对较重的特点，表明原油在成藏后经历了短期高温热事件的影响。     

塔里木盆地寒武系—奥陶系烃源岩油源特征与超深层油气来源

塔里木盆地寒武系—奥陶系烃源岩的生源特征及其对超深层油气贡献是塔里木盆地超深层海相油气勘探面临的关键地质问题。根据分子与同位素地球化学分析和生烃热模拟实验研究,系统梳理油源对比的地球化学参数,认为原油中C26~C30甾烷的分布、伽马蜡烷指数、三环萜烷与五环萜烷比值和正构烷烃同位素等油源示踪指标,易受热演化程度、生物降解和水岩氧化还原作用影响,掩盖母源输入和沉积环境的差异。正构烷烃奇偶优势,异常的三环萜烷分布,全油和正构烷烃δ13C同位素明显偏重以及高含量的多环芳烃的出现主要归因于高过成熟热演化作用、低温热液或侵入岩浆等异常热事件的影响,而并非反映—O1烃源岩中生烃母质的地球化学特征。局部的硫酸盐热化学还原反应导致无机硫并入形成次生的噻吩类化合物,造成有机硫同位素值明显升高,无法反映母源特征,目前被选做寒武系典型烃源岩和端元油的生烃母源特征很可能是经历多种次生地球化学作用改造的结果。通过分析寒武系—奥陶系两套中等热成熟度烃源岩的形成环境和生物母质类型,表明塔里木盆地台盆区寒武系—奥陶系烃源岩的油源特征差异主要受控于沉积相,塔北中西部海相原油主要与透光厌氧环境烃源岩有关,塔中地区原油主要来源于深水盆地相烃源岩。重新建立不同物化性质原油与高过成熟烃源岩之间可靠的油 源对比参数,需要同时考虑成熟度和次生改造等复杂地球化学作用的多重影响才能确定其成因和来源。     

塔里木盆地寒武-奥陶系烃源岩萘、菲系列化合物单体碳同位素特征

为了揭示塔里木盆地海相烃源岩中芳烃分子同位素的地质-地球化学信息,利用逐步增加试剂极性的方法对芳烃馏分进行了进一步的分离,并利用气相色谱同位素质谱(GC-IR-MS)分析技术测定了萘系列和菲系列的单体碳同位素.分析结果显示,芳烃分子碳同位素分布为-47.5‰ ～-17.4‰,其中寒武系-下奥陶统烃源岩的碳同位素为-38.2‰ ～-17.4‰,平均为-26.8‰;其中ML1-1、ML1-2两个样品的碳同位素为-36.8‰ ～-17.4‰,平均为-25.7‰;中-上奥陶统烃源岩为-47.5‰ ～-20.3‰,平均-30.6‰.结果表明,萘系列和菲系列化合物整体上表现为寒武系-下奥陶统烃源岩富集13C,而中-上奥陶统烃源岩更富集12C;在受到异常高温作用或过成熟度阶段,成熟度可能对芳烃的分子碳同位素产生较大影响,使其更富集13C.不同样品的二甲基萘系列化合物的碳同位素分布特征相似,暗示其可能具有相似的碳同位素分馏机制.而三甲基萘、二甲基菲系列化合物的碳同位素分布杂乱,暗示其成因来源可能较为复杂.塔里木盆地两套海相烃源岩中1,6-DMN、1,2,5-TMN、1-MP和1,9-DMP的碳同位素存在明显差异,可以对两套烃源岩进行有效的区分.     

塔里木盆地凝析油单体烃碳同位素特征与成因分析

对采自塔里木盆地不同地区和层位的１４个凝析油样进行了ＧＣ/Ｃ/ＭＳ在线（Ｏｎｌｉｎｅ）碳同位素分析，获得了液态烃系列单分子碳同位素组成资料。在此基础上，探讨了不同时代凝析油的单体烃碳同位素特征，并进行了油－油的对比与成因分类。结果表明，塔里木盆地存在煤成油、油型油与混合成因油三种类型。其中油型油又可按母岩的时代划分为奥陶系（寒武系）、石炭系、三叠系三种类型。煤成油的源岩为佛罗系煤系源岩。佐证了该盆地存在四套现实的烃源岩（即奥陶－寒武系、石炭系、三叠系和侏罗系）。     

塔里木盆地原油的成因研究

对塔里木盆地原油和生油岩饱和烃进行ＧＣ－Ｃ－ＭＳ和ＧＣ－ＭＳ分析，利用单个正构烷烃碳同位素组成和三环萜烷分布特征进行油源对比，研究了塔里木盆地原油的油源问题；根据寒武—奥陶系富含菌藻有机质生油岩饱和烃色谱分析结果，对塔里木盆地海相原油含蜡较高的成因进行了探讨     

Source of 1,2,3,4-tetramethylbenzene in asphaltenes from the Tarim Basin

1-Alkyl-2,3,6-trimethylbenzenes and a high relative amount of 1,2,3,4-tetramethylbenzene (TTMB) have been previously detected in the marine oils and asphaltenes in the oils from the Tarim Basin. In the present study, the stable carbon isotopic compositions of TTMB and n-alkanes in the pyrolysates of asphaltenes in the marine oils from the northern Tarim Basin and Silurian tar sands from the Tarim Basin were determined. TTMB has stable carbon isotopic compositions in the range from −23‰ to −24‰ and are about 12‰ more enriched in ¹³C than concomitant n-alkanes (−35‰ to −37‰) in the pyrolysates. The results indicate a contribution from green sulfur bacteria (Chlorobiaceae) to TTMB. Thus, the depositional environments of the source rocks for the marine oils and the bitumen in tar sands from the Tarim Basin are characterized by periods of euxinic conditions within the photic zone.     

Carbon isotopic composition of individual n-alkanes in asphaltene pyrolysates of biodegraded crude oils from the Liaohe Basin, China

Biodegraded oils are widely distributed in the Liaohe basin, China. In order to develop effective oil-source correlation tools specifically for the biodegraded oils, carbon isotopic compositions of individual n-alkanes from crude oils and their asphaltene pyrolysates have been determined using the gas chromatography–isotope ratio mass spectrometry technique. No significant fractionation in the stable carbon isotopic ratios of n-alkanes in the pyrolysates of oil asphaltenes was found for anhydrous pyrolysis carried out at temperatures below 340°C. This suggests that the stable carbon isotopic distribution of n-alkanes (particularly in the C₁₆–C₂₉ range) in the asphaltene pyrolysates can be used as a correlation tool for severely biodegraded oils from the Liaohe Basin. Comparison of the n-alkane isotopic compositions of the oils with those of asphaltene pyrolysates shows that this is a viable method for the differentiation of organic facies variation and post-generation alterations.     

Origin of Crude Oil in the Lunnan Region,Tarim Basin

<正>The oil source of the Tarim Basin has been controversial over a long time.This study characterizes the crude oil and investigates the oil sources in the Lunnan region,Tarim Basin by adopting compound specific isotopes of n-alkanes and biomarkers approaches.Although the crude oil has a good correlation with the Middle-Upper Ordovician(O_(2+3)) source rocks and a poor correlation with the Cambrian-Lower Ordovician((?)-O_1) based on biomarkers,theδ~(13)C data of n-alkanes of the Lunnan oils show an intermediate value between(?)-O_1 and O_(2+3) genetic affinity oils,which suggests that the Lunnan oils are actually of an extensively mixed source.A quantification of oil mixing was performed and the results show that the contribution of the Cambrian-Lower Ordovician source rocks ranges from 11%to 70%(averaging 36%),slightly less than that of the Tazhong uplift.It is suggested that the inconsistency between the biomarkers andδ~(13)C in determining the oil sources in the Lunnan Region results from multiple petroleum charge episodes with different chemical components in one or more episode(s) and different sources.The widespread marine mixed-source oil in the basin indicates that significant petroleum potential in deep horizons is possible.To unravel hydrocarbons accumulation mechanisms for the Lunnan oils is crucial to further petroleum exploration and exploitation in the region.     

塔北隆起深层海相油藏中原油及族组分碳同位素组成的纵向分布特征及其地质意义

利用MAT252同位素质谱仪分析了塔里木盆地塔北隆起深层海相油藏中原油及族组分的碳同位素组成。研究表明该区深层海相油藏中原油的全油碳同位素组成主要受生源控制,受热力作用影响较小;而在继承生源的碳同位素组成的基础上,热力作用将对原油族组分的碳同位素组成及其逆转和分馏产生重要影响。总的趋势是随着油藏埋藏深度的增大和热力作用的加强,饱和烃组分的碳同位素组成逐渐变重,而沥青质组分的碳同位素组成不断变轻,族组分碳同位素逆转程度和分馏程度有所加强,并出现饱和烃﹥芳烃﹥非烃﹥沥青质的整体逆转现象。塔北隆起深层海相原油族组分的碳同位素组成的纵向变化特征,可以反映出热力作用对原油稳定性的影响。     

Comparative studies on compounds occluded inside asphaltenes hierarchically released by increasing amounts of H2O2/CH3COOH

Being the heaviest fraction of crude oils, asphaltenes are liable to aggregate, and other molecules in the oils can be steadily adsorbed onto, and even occluded inside the macromolecular structures of the asphaltenes. These occluded compounds inside the asphaltenes can survive over geological time in oil reservoirs owing to effective protection by the macromolecular structures of the asphaltenes. The asphaltenes of a crude oil (ZG31) from the central Tarim Basin, NW China, were hierarchically degraded by increasing the amount of H₂O₂/CH₃COOH to release the occluded compounds. Besides the common components, series of even numbered n-alk-1-enes and 3-ethylalkanes were detected among the occluded compounds. Comparison of the biomarker distributions and the compound-specific C isotopic results between the compounds from the maltenes and those from the occluded fraction, the ZG31 reservoir was suggested to have been charged multiple times, with different charges being derived from different strata of source rocks.     

Molecular fossils and sources of Cambrian heavy oil of Well Tadong-2 in the Tarim Basin,Xinjiang, China

Research on the molecular fossil characteristics of heavy oil from Well Tadong-2 is of great importance to constrain the source of marine crude oils in the Tarim Basin, Xinjiang, China. The authors synthetically applied the isotope mass spectrograph, chromatography and chromatography-mass spectrography to the studies of molecular fossil characteristics of heavy oil from Well Tadong-2 in the Tarim Basin, and the results obtained revealed that heavy oil from Well Tadong-2 is characterized by high gammacerane, high C₂₈ sterane, low rearranged sterane and high C₂₇-triaromatic steroid, these characteristics are similar to those of Cambrian-Lower Ordovician source rocks, demonstrating that Cambrian crude oils came from Cambrian-Lower Ordovician source rocks; condensed compounds (fluoranthene, pyrene, benzo[a]anthracene, bow, benzo fluoranthene, benzopyrene) of high abundance were detected in heavy oil from Well Tadong-2, and the carbon isotopic values of whole oil are evidently heavy, all the above characteristics revealed that hydrocarbons in the crude oils became densified in response to thermal alteration.