含水体系中二苯并噻吩热稳定性的实验研究

Molecular markers have been applied in petroleum researches widely. Generally, they are organic matters with special and stable structure in a trace level concentration. They are usually proposed as indicators of the depositional environment and lithology of the parent source rock. Moreover, sulfur is the third important element in organic geochemical studies, and its presence makes troubles in either petroleum refined process or environment pollutions. Therefore, the sulfur-bearing molecular markers are indispensable and of profound significance for investigations on the thermal stability of biomarker under the conditions of oil generation and reservoir layer, and on their sources, generations, and migrations. Furthermore, it can improve the understanding on the organic hypothesis, as well as their transformation during the refining process..With the development of the experimental geochemical techniques, the thermal simulation experiments have been employed in the organic geochemistry studies. Moreover, some pure model organic compounds have been investigated on their mechanisms of the thermal pyrolysis. However, in the nature, the processes of petroleum generations, migrations, and reservoirs are normally involved with water. Moreover, the role of water has been suggested very important during the petroleum formation. Thus, it is much closer with the actual geological environment to investigate the thermal stability and the mechanism of the thermal evolution of biomarkers in a water-bearing system. .Our group is planning to investigate the thermal stability of dibenzothiophene in water-free or water-bearing system with thermal simulation experiments and in-situ Raman observations, and treat pristane as a referrence. We would like to look for more detailed geochemical data from the experiments, and try to reveal their reaction mechanism on the molecular level. The aim of this proposal is to speculate the potential thermal transformation based on the experiment results and try to make reasonable explanations for this molecular marker.

分子标志化合物在石油中有广泛的应用。它们对石油的生成、来源及运移有重要的示踪作用，同时对源岩的岩性和沉积环境起到指示作用。硫是有机地球化学领域中第三重要的元素。研究含硫的分子标记物在生油层和储层温压条件下的稳定性，以及它们的来源、形成方式和反应产物，对准确地理解其作为分子标志物的潜在机理有至关重要的意义，同时也会对理解含硫多环芳烃在石油精炼过程中的形态变化有所帮助。在自然界中，石油生成、运移和储藏的环境多与水有关，而且水在石油生成过程中发挥的重要性已被所认识并接受。因此，研究含水体系中分子标志物的热稳定性和热演化过程及机理，将更贴近真实的地质条件。.本课题以二苯并噻吩这种典型的含硫分子标志物作为研究对象，并以姥鲛烷作为参照，旨在通过热模拟实验和原位谱学观测获得它们在含水条件下的地球化学数据，从分子层面寻找其潜在的转变机理，从而对其作为分子标志物的机理提出更合理的解释。

项目围绕拟解决的科学问题，用黄金管热模拟实验装置和金刚石压腔模拟地层深部的温压条件，研究二苯并噻吩（DBT）在含水条件下的热稳定性及其影响因素。结果表明，适量的水在DBT裂解反应当中具有促进作用，但是过量的水则会产生抑制作用。当实验条件低于水的临界温度375 °C，长达4天的实验中，DBT也几乎不反应（等效Easy%Ro约为1.25%）。这表明在有机质成岩作用和后生作用阶段，DBT具有很强的热稳定性。当实验温度范围介于450 ºC~480 ºC之间时，可以检测出明显的裂解产物。在450 °C、50 MPa下，恒温4天的实验中DBT的转化率低于3%。该条件的等效Easy%Ro约为2.76%，相当于有机质演化的高过成熟阶段。这表明热成熟作用对于DBT的破坏作用较小，在有机质热演化过程中，DBTs因热蚀变等次生作用发生剧烈改造的可能性非常小。另外，实验中并没有观察到DBT在水热解过程中转换成二苯并呋喃。结合上述成熟度对DBT稳定性影响的认识，表明由于DBT在形成后具有足够的稳定性，所以“三芴”指标用于判识原油或烃源岩沉积环境时，是有一定理论依据的，可以排除在有机质后生作用阶段的热演化对其地化意义的影响。.我们进一步研究了DBT在沉积有机质成岩演化过程中可能的生成机理。发现在有S存在的时候，联苯类化合物可能是对应的结构的DBT同系物的反应前身物，验证了我们课题组以前提出的假设。并且，我们发现在温度低至200 °C的中就有DBT的生成，因此我们推测DBTs在地质条件下，由于压力和地质矿物催化性能的原因，通过该机理的生成DBT所需要的温度门槛可能更低。.综上所述，该项目的研究成果揭示了DBTs在沉积盆地或者油藏中的热稳定性较高，适合用于深层/超深层油气勘探的地球化学指标。深入研究DBTs的形成机理和热演化行为将使这些指标的地质意义更加清晰，对指导勘探更为有效。