塔里木盆地海相原油中一类长链烷基苯的检出、结构鉴定及其地质意义

Long-chain alkylbenzenes, which are widespread in various sedimentary organic matters and show large variations in the molecular structure, are very important to the oil/source correlation, elucidating the depositional environment and the study of the diagenesis. Besides reported aryl isoprenoids in marine oil from the Tarim Basin, the applicant has detected a series of long-chain alkylbenzenes from m/z133+134 mass chromatograms of the aromatic fractions of these oil and their relative amount showed clear relationship with the carbon isotopic signatures of oil. However, the molecular structure of these alkylbenzenes is not known, yet. Based on the characteristics of retention time and mass spectrum of them, a trimethyl substituted n-alkylbenzene structure was tentatively assigned, and one C15 isomer has been synthesized using the Friedel-Crafts reaction by the applicant and cooperator. All these results provided a good beginning for further work. On the basis of the preliminary work, we would like to carry out three types of studies once the applicant was proved to be granted: 1) Accurate assignments of molecular structure of the unknown alkylbenzenes by the synthesis of reference samples and co-injection of them with oil sample. 2) The distribution of the unknown alkylbenzenes in Tarim oil and its relationship with indices of source and maturity will be investigated in detail to preliminarily decide the source and geological implication of these compounds. 3) Thermal simulation will be performed on synthesized reference sample and the oil sample at low maturity stage from the Tarim Basin to elucidate the source and the tendency of thermal evolution of the unknown alkylbenzenes. Moreover, for comparison, similar work will also be carried out with oil or kerogen sample from other area, in which no aryl isoprenoids were found. This study is expected to wide our knowledge of long-chain alkylbenzenes and provide new clues to understanding the genesis of oil from the Tarim Basin.

长链烷基苯广泛存在于各类沉积有机质中，结构变化大，对油/源对比、沉积环境与成岩作用等研究具有重要意义。除了已报道的芳基类异戊二烯烷烃，申请人近期在塔里木盆地海相原油芳烃m/z133+134质量色谱图中检出了一类长链烷基苯，其相对含量与原油碳同位素组成有关，结构有待确认。申请者根据保留时间和质谱特征初步推断其可能为三甲基-正烷基苯，并与合作者采用傅-克反应合成了1个C15异构体，取得了良好开端。 以此为基础，我们申请开展三方面的工作：1）采用标样合成、共注的方法力争准确鉴定未知烷基苯的结构；2）分析原油中未知烷基苯的分布及其与母源、成熟度指标的相关性，推断其来源和地质意义；3）对合成标样、演化程度较低的塔里木原油和其它地区未检出芳基类异戊二烯烷烃的原油/烃源岩干酪根开展热模拟研究，阐明未知烷基苯的来源与热演化规律。 本次工作有望丰富长链烷基苯的理论认识，为塔里木原油的成因研究提供新线索。

本课题利用有机化合物合成和共注方法对塔里木盆地海相原油中检出的三甲基烷基苯进行了结构鉴定，在此基础上利用色谱-质谱分析了芳基类异戊二烯和三甲基烷基苯的分布特征及其与母源、成熟度指标的关系，结合原油不同组分的热模拟实验对这类化合物的成因进行了研究。本课题主要获得三个认识：首先，合成了三甲基正烷基苯的5个异构体，结合特殊色谱柱分离实验结果，确认了塔里木盆地海相原油中利用常规色谱柱检出的相对含量较高的三甲基烷基苯系列应为2,4,5-和2,3,5-三甲基的共流出系列。第二，芳基类异戊二烯类化合物主要在热演化程度较低的重油和正常黑油中检出，而2,4,5-/2,3,5-三甲基正烷基苯在热演化程度高的轻质油和蜡质油中相对含量较高。两个系列烷基苯的相对含量变化主要与原油的热演化程度有关。由此建立了两类化合物与原油正构烷烃碳-氢同位素的联系，为综合利用分子组成和同位素进行深层原油成因研究提供了示例。最后，结合原油不同组分热模拟实验与原油正构烷烃的碳-氢同位素组成，认为塔里木盆地原油地球化学特征总体上受控于一类烃源的热演化过程，但要充分考虑母源非均质性的影响。储层原油总体裂解程度不高，但重质组分的二次裂解是影响原油分子和同位素组成的重要过程，为塔里木盆地深层原油稳定性提供了进一步约束。