【作者】 沈斌；

【导师】 汪双清；

【作者基本信息】 中国地质科学院 ， 分析化学， 2008， 硕士

【摘要】 位于青藏高原的羌塘盆地是我国陆上勘探程度相对较低的具有较好勘探前景的含油气盆地,由于特殊的地理和地质条件,对于羌塘盆地的油气勘探还存在许多亟待研究解决的地质科学问题和技术方法问题。本文通过对164块采自羌塘盆地中生代主要烃源岩层系的地表烃源岩样品和钻井岩芯样品进行的系统石油地球化学分析测试,研究了羌塘盆地主要烃源岩层系的有机地球化学特征,以期为深入研究该区的油气生、运、聚规律提供石油地球化学依据。大量有机地球化学数据表明,羌塘盆地侏罗系和上三叠系烃源岩的有机质成熟度普遍很高,处于高成熟—过成熟阶段。干酪根镜质体反射率（R_o）均在2.8%以上;绝大部分烃源岩的岩石热解最大峰温值在455℃以上;干酪根中腐泥组和壳质组显微组分消失,已转化为次生的微粒体、各向异性体和镜状体;烃源岩中的有机质基本上是残留有机质,烃源岩热解分析,可溶烃S₁=0.04mg/g,热解烃S₂在0.01～0.10mg/g,残余碳S₄为0.01～11.11mg/g,沥青A含量在0.0005%～0.0283%。羌塘盆地烃源岩中的有机质丰度普遍不高,但总有机碳含量比较稳定。泥岩和页岩的总有机质含量在0.03～0.52%,碳酸岩总有机质含量在0.05～1.22%,按照有关烃源岩等级划分标准,以中等烃源岩和好烃源岩为主。羌塘盆地侏罗系烃源岩的沉积环境为海相还原环境。Pr/Ph值在0.18～0.8之间。有机质母质主要为低等水生生物,有高等植物的混入。nC₂₁-/nC₂₁₊值在0.84～2.18之间,以大于1为主;正构烷烃大部分以nC₁₇为主峰碳,少数为nC₂₇。C₂₇、C₂₈、C₂₉规则甾烷呈不规则“V”字型分布,C₂₇和C₂₉的丰度大致相当。高程度热演化对羌塘盆地中生代烃源岩的分子地球化学特征有显著影响。甾、萜类化合物遭受严重破坏,并生成了丰富的高稠合度多环芳烃和烯烃系列化合物,碳同位素组成也被明显歧化。风化作用对羌塘盆地地表烃源岩的地球化学信息有明显的改造作用。地表烃源岩有比井下烃源岩明显低的总有机碳丰度和可溶有机质丰度,岩石热解峰温值明显升高;地表干酪根中氧、氮原子流失明显,元素组成变得没有地层规律。更多还原

【Abstract】 Qiangtang Basin is considered to be of good prospect for oil and gas exploration. Due to that it is located in the Qinghai-Tibet Plateau under special geographical and geological conditions, it remains low level explored so that many geoscientifical and exploration methodological problems need to be solved. Based on a series of organic geochemical analyses of 164 outcrop and core source rocks collected from Qiangtang Basin, this thesis reports the results of a study on the petroleum geochemical characteristics of the main Mesozoic source rocks of Qiangtang Basin in order to provide some fundamental references for the studies on the oil generation, migration and accumulation history and patterns in the basin.The organic geochemical data shows that the organic matter in the Jurassic and Triassic source rocks in Qiangtang Basin has a very high maturity at high mature-postmature stage. The vitrinite reflectance of kerogen （Ro） is above 2.8%. The T_max values of Rock-Eval analyses are above 455℃for most of the source rocks. The inertinites and liptinites （formerly called exinite） disappear from kerogen due to that they are derived into secondary maceral groups. Furthermore, the organic matter in the source rocks is basically proved to be of only residues. The Rock-Eval pyrolysis of source rocks shows that the content of S₁ component takes 0.04 mg/g as the maximal, S₂ component ranges 0.01-0.10 mg/g, while S₄ component dorminates with its content up to 11.11 mg/g. The content of chloroform bitumen A is only 0.0005% to 0.0283% as well.The abundance of organic matter in the source rocks is very low, and the TOC value varies within a narrow range. The TOC values of the mudstones and shales range from 0.03% to 0.52%, while those of the carbonate source rocks range from 0.05% to 1.22%. According to the relevant source rock classification criterion, source rocks in Qiangtang Basin belong to medium to good source rock classes.The sedimentary environment of Jurassic source rocks in Qiangtang Basin was marine and reductive. The Pr/Ph ratio ranges from 0.18 to 0.8 while most source rocks have the value smaller than 1. The nC₂₁/nC₂₁+ value lies between 0.84 and 2.18 while most of the values greater than 1. The organic matter is mainly derived from aquatic organisms together with small amount of terrestrial organism input. Most of the source rocks demonstrate a single-peak type distribution pattern of n-alkanes with the highest peak of C₁₇ component. The regular steranes show a "V" type distribution pattern, in which the abundance of C₂₇- and C₂₉-steranes is roughly equal.The high level thermal evolution has seriously affected the molecular geochemical characteristics of the Mesozoic source rocks in Qiangtang Basin. Both steranes and terpanes suffered serious damage, and plenty of polyaromatics and alkenes were derived as the result. Even the carbon isotope composition has been obviously altered as well.The geochemical information of the outcrop source rocks in Qiangtang basin is obviously altered by weathering effection. The outcrop source rocks have clearly lower TOC content and lower abundance of soluble organic matter than those of core source rocks, but the T_max value of Rock-Eval analysis obviously increases. The oxygen and nitrogen in Kerogen of the outcrop source rocks loss so obviously that the composition of the organic elements shows no regularity varying with the formations what is held by the core source rocks.更多还原