生排烃过程中的烃源岩和原油Re-Os体系

The generation of crude oil is a crucial part of the evolution of petroleum systems. Rapid progress has been achieved on the Re-Os dating of crude oil generation in recent years. The current hydrous pyrolysis experiments of source rock have provided insights into the Re-Os systematics during crude oil generation, however, the closed-system applied is unable to simulate the process of crude oil expulsion properly. Thus, the change of the source rock Re-Os systematics before and after the expulsion, and its relationship with that of the expelled and residual oil remain ambiguous. Meanwhile, studies have shown that there are differences in the Re-Os elemental and isotopic systematics among the fractions of some crude oils which have led the research on Re-Os systematics into the new level of the internal fractions of crude oil. The Re-Os systematics of the crude oil fractions at the key timing of oil generation and its evolution during key process of expulsion are crucial for the Re-Os geochronology. This research plans to explore the relationship of Re-Os systematics among the expelled oil, residual oil and source rock through the semi-open system pyrolysis of source rock. Meanwhile, this study will fractionate the expelled and residual oil for the exploration of their internal Re-Os systematics right after generation. This Re-Os systematics study of the key elements of petroleum systems during the generation and expulsion of crude oil shall facilitate the understanding and optimization of the Re-Os dating of source rock and crude oil.

原油生成是含油气系统演化的重要一环，其年龄的Re-Os定年法近些年来发展迅速。已有的烃源岩热模拟生烃实验研究了生油过程中的Re-Os地球化学行为，但其封闭体系装置不能很好的模拟排烃过程。因此，排烃前后烃源岩Re-Os体系的变化及其与排出油、残留油之间的关系尚不明确。研究表明一些原油的次组分之间存在Re-Os元素丰度和同位素组成的差异，这使对Re-Os体系特征的研究进入到了原油的次组分这个新的层面。原油次组分Re-Os体系在生油时的特征和排烃过程中的演化对Re-Os定年相当重要。本研究拟通过半开放体系的烃源岩热模拟生排烃实验，研究排出油、残留油和烃源岩之间的Re-Os体系关系；同时，拟将排出油和残留油细分为多个次组分以研究原油在其初生成时的次组分Re-Os体系。本课题对生排烃过程中各要素Re-Os体系的研究将有利于理解和优化烃源岩和原油的Re-Os定年。

经济可采油气藏的形成需要生、储、盖、圈、运、保等要素和过程在空间和时间上的配合，烃源岩成熟、原油生成时间是研究油气藏形成与分布规律的关键问题。近年来，Re-Os放射性同位素体系越来越多的被应用于原油生成期的定年。本项目对烃源岩热模拟生烃、烃源岩及其原油的Re-Os体系关系以及对优化原油Re-Os定年相当重要的原油次组分分离方法进行了研究，通过对烃源岩与原油Re-Os体系特征的理解提升定年的精确度。..本研究中河北省下花园地区中元古代下马岭组烃源岩具有良好的生油能力和较高的Re含量，其生排烃过程中Re和Os从烃源岩向原油的转移对原油中Re和Os的来源问题及相关的原油Re-Os定年方法及地质意义等问题具有重要意义。成熟烃源岩中抽提沥青的研究表明，抽提沥青的Re和Os含量低于烃源岩和干酪根，生油过程中干酪根中Re和Os向原油的转移是有限的。这与原油中Re和Os含量普遍偏低的现象一致，表明高Re和Os含量的原油及沥青可能具有烃源岩之外的Re和Os的来源。..本研究的原油次组分细分方法专利涉及石油化工技术领域，提供了一种分离原油沥青质次组分的方法。本方法通过逐步增加沉淀剂的比例，诱导沥青质次组分根据稳定性的不同从原油或沥青中逐步分离出来。相对于传统的先沉淀出来沥青质再分离沥青质次组分的方法，本方法更接近真实地质情况，不存在沥青质先沉淀再溶解过程中可能出现的复杂的沥青质分子絮凝、吸附、沉淀、再溶解和解吸的过程，能更贴切地模拟真实的原油沥青质次序沉淀过程。本发明提供的方法能够模拟原油中不稳定沥青质次组分在地下逐步散失的过程，为石油生产中的沥青质危害问题和油气地球化学研究中的元素、同位素、特征化合物等变化研究提供帮助。