Laboratory Experiments to Determine the Origin of High Molecular Weight Hydrocarbons (>C40) in Geological Samples

生物标志物是地质样品中的化合物，其基本碳骨架与藻类、细菌和高等植物等源物质中的前体相似。迄今为止发现的大部分生物标志物都在C10-C40范围内。过去，色谱法和质谱法的局限性阻碍了对C40以上区域生物标志物的成功研究。在过去的两年中，我们利用高温毛细管柱和串联质谱的发展优势，进入了C40-C100范围内生物标志物地球化学的前沿领域。用串联质谱法结合气相色谱法或直接插入探针对各种样品的提取物进行了研究。串联质谱技术与微热解技术相结合，对热解降解干酪根和沥青质的高分子量片段进行了研究。这项工作清楚地证明了在各种样品中存在高分子量组分的复杂混合物。这些化合物主要由延伸到至少C100的正构烷烃和烷基环己烷组成。除了分析限制外，这些组分没有像低于C40的组分那样被彻底研究的另一个原因是，在许多情况下，它们的低挥发性排除了它们在井口收集的原油中的存在。此外，这些组分的低挥发性也意味着它们可能不一定出现在含有低于C40的化合物的饱和馏分中。目前的目标是研究这些分子量化合物是如何形成的。在一些初步实验中，我们已经表明，脂肪酸的人工成熟将导致这些化合物的聚合，形成高分子量的烷烃、环己烷和烷基化萘的复杂混合物。建议扩展这些实验，并在存在和不存在催化剂（如膨润土）的情况下，在各种温度下，用各种脂类以及天然存在的有机材料（如高等植物材料和藻类）进行实验。在单质硫存在的情况下也进行了初步实验，结果表明，许多反应产物中都含有硫。虽然以前也进行过类似的成熟实验，但早期的实验通常是为了检测热降解产物，而不是聚合产物。本文所描述的工作将为我们提供有关这些高分子成分可能产生的方式和这些化合物形成的条件的信息。

Biomarkers are compounds in geologic samples whose basic carbon skeleton resembles that of their precursors which occur in source materials such as algae, bacteria and higher plants. For the most part the biomarkers discovered to date have been in the C10-C40 range. Limitations in both chromatography and mass spectrometry in the past, have prevented the successful investigation of biomarkers in the region above C40. In the past two years we have taken advantage in the development of high temperature capillary columns and tandem mass spectrometers to enter into the frontier area of biomarker geochemistry in the range of C40-C100. Extracts from a variety of samples have been investigated by tandem mass spectrometry in combination with gas chromatography or the direct insertion probe. Tandem mass spectrometry has been used in combination with micropyrolysis techniques to investigate the high molecular weight fragments produced by pyrolytic degradation of kerogens and asphaltenes. This work has clearly demonstrated the presence of complex mixtures of high molecular weight components in a wide variety of samples. These compounds are dominated by n-alkanes and alkylclohexanes extending to at least C100. In addition to analytical limitations, another reason why these components have not been investigated as thoroughly as components below C40 is that in many cases their low volatility precludes their presence in crude oils collected at the well head for example. Furthermore the low volatility of these components also means it is possible that they may not necessarily occur in the saturate fraction containing compounds below C40. The present goal is to investigate how these molecular weight compounds are formed. In some preliminary experiments we have shown that artificial maturation of fatty acids will lead to polymerization of these compounds to form high molecular weight alkanes, cyclohexanes and complex mixtures of alkylated naphthalenes. It is proposed to expand these experiments and perform them with a variety of lipids, as well as naturally occurring organic material such as higher plant material and algae, in the presence and absence of catalysts, such as bentonite, and at a variety of temperatures. Preliminary experiments have also been conducted in the presence of elemental sulphur and it has been shown that sulphur is incorporated into many of these reaction products. Although similar maturation experiments have been performed previously, the earlier experiments were typically designed to examine thermal degradation products and not polymerization products. The work described herein will provide us with information on the way in which these high molecular components may be produced and conditions under which these compounds will be formed.