热演化对潜江组盐间页岩油赋存状态与滞留行为的影响

Multiple inter-salt rhythms are widely developed in the Qianjiang Formation of the Jianghan Basin, which is one of shale oil research and exploration hot spots in China. Each inter-salt rhythm with high oil content and effective sealing capacity by the upper and lower salt layers makes for a separate, relatively closed, petroleum system. The movability of shale oil is largely related to occurrence state, reservoir space, and physical and chemical properties of hydrocarbon fluid in the shales. However, geological cognition is still needed to be deepened in the mobility and flowing law of inter-salt shale oil. Previous studies on the occurrence state and retention behavior of inter-salt shale oil were rarely undertaken from the perspective of the nature of both kerogen and generated hydrocarbons during thermal maturation. In this study, a thermal maturation shale sequence was obtained by thermo-compression simulated experiments, and shale oils with different occurrence states were separated from the shales through stepwise extraction. The reservoirs physical properties and organic geochemical characters of the shales, structural composition of kerogen, and molecular compositions of both hydrocarbon and non-hydrocarbon fractions in the shale oils, were characterized by combining manifold analysis methods. Furthermore, to elucidate the effect of thermal maturation on the occurrence state and retention behavior of inter-salt shale oil, the coupling relationship between kerogen and shale oil at varying maturation stages were discussed on the basis of geological model of hydrocarbon-pore-surface. This project is of great significance to the movability evaluation of inter-salt shale oils.

江汉盆地是我国当前页岩油研究和勘探的热点地区之一，其潜江组发育多个盐韵律层，上下盐岩形成有效封堵，页岩含油率高，有利于形成相对封闭的页岩油系统。页岩油的可动性与页岩中烃类流体的赋存状态、赋存空间及物理化学性质等有关，但目前对盐间页岩油的可动性和流动规律等地质认识仍有待深化。以往的研究工作较少从有机质热演化过程中干酪根和生成的液态烃性质的演变来研究盐间页岩油的赋存状态和滞留行为。本项目拟通过开展烃源岩的热模拟实验获得不同热成熟度的盐间页岩样品，然后采用分级抽提法来定量表征不同赋存状态的页岩油，并结合各种地球化学分析测试手段来表征页岩储集物性、有机地化特征、干酪根结构以及页岩油烃类和非烃组分的组成。最后，在盐间页岩的烃−孔隙−表面模型基础上，分析不同热演化阶段干酪根和页岩油的耦合关系，探讨热演化对盐间页岩油赋存状态和滞留行为的影响。本项目对盐间页岩油可动资源量评价具有重要的指导意义。

随着常规石油资源的消耗，非常规油气资源受到越来越多的重视，并逐渐成为当今油气勘探领域的热点。江汉盆地潜江凹陷盐间页岩具有形成规模页岩油资源的潜力。页岩油的可动性与页岩中烃类流体的赋存状态、赋存空间及物理化学性质等有关，但目前对盐间页岩油的可动性和流动规律等地质认识仍有待深化。以往的研究工作较少从有机质热演化过程中干酪根和生成的液态烃性质的演变来研究盐间页岩油的赋存状态和滞留行为。本项目通过开展烃源岩的热模拟实验获得不同热成熟度的盐间页岩样品，采用分级抽提法来定量表征不同赋存状态页岩油，结合各种地球化学分析测试手段来表征页岩储集物性、有机地化特征、干酪根结构以及页岩油烃类和非烃组分的化学组成；在此基础上，探讨热演化对盐间页岩油赋存状态和滞留行为的影响机制。研究结果表明：盐间页岩油可划分为游离态和束缚态两大类，其含量和化学组成均存在明显的差异。游离态页岩油以具有弱极性或非极性的饱和烃、芳烃以及中性含杂原子化合物为主；而束缚态页岩油则以含有大量极性官能团的胶质和沥青质重质组分为主，它们易于与无机矿物或干酪根通过离子键和/或氢键等方式结合。随着热成熟度的增加，干酪根结构中的脂肪族结构单元逐渐减少，支链化程度降低，残余干酪根的芳香度逐渐增加；与此同时，干酪根裂解生成的液态烃产物中烃类含量逐渐增加而胶质和沥青质等重质组分逐渐减少。干酪根和液态烃在分子结构和性质上的演变，导致两者的相互作用强度在不同热演化阶段发生变化。此外，在较高热成熟阶段，形成更多的小分子烃类改善了烃类流体的流动性, 排烃作用相应增强, 导致盐间页岩油含量发生变化。本项目能够为盐间页岩油可动性评价提供相关理论支持。