Abstract: Shale oil has become an important alternative resource for oil and gas in China. Scientifically objective grading assessment of shale oil resources can provide technical support and a reference basis for oil and gas exploration and commercial hydrocarbon development. The key to shale oil resource assessment is the determination of oil content. There are numerous commonly used methods for evaluating oil content; however, due to the significant differences in geological conditions of continental basins, the assessment results are subject to uncertainty. Based on a systematic review of the methods and models for evaluating oil content in lacustrine shale, the advantages and disadvantages of various oil content assessment methods are discussed. Furthermore, based on the existing research findings, the paper proposes a new shale oil resource grading assessment model, which comprehensively considers the dynamic coupling between oil content, mobility, and geological parameters. The research results show as follows. (1) The new model uses free hydrocarbon content (S₁), total organic carbon (TOC) content, and the ratio of S₁ to TOC content as grading parameters, dividing the resources into four categories, i.e., enriched resources, moderately enriched resources, low-efficiency resources, and ineffective resources. (2) The envelope curve of S₁ variation with TOC content in typical shale basins exhibits a normal distribution pattern. When TOC content is too low or too high, the enrichment degree of shale oil resources is controlled by the source rock quality and reservoir properties, respectively. (3) In the Permian Fencheng Formation of Mahu sag in Junggar Basin and the Cretaceous Qingshankou Formation of Qijia-Gulong sag in Songliao Basin, the upper and lower limits of TOC contents in their respective shale oil enrichment areas are 0.4 % and 2.2 %, and 1.5 % and 3.4 %, with the favorable shale oil areas distributed in a circumferential pattern around the hydrocarbon generation centers. The advantages of the new model lie in: (1) considering the influences of source rock quality, reservoir properties, and their coupling relationship at the basin scale on shale oil enrichment; (2) being able to characterize the degree of shale oil resource enrichment from two perspectives, i.e., shale oil content and mobility. The model corrects the misconception that oil content remains constant after TOC content reaches a certain value, providing a basis for scientifically evaluating shale oil resources.

Key words: continental shale, oil content, assessment method, resource assessment, grading assessment, enriched resource

摘要： 页岩油目前已成为中国油气资源重要的接替类型,科学客观地开展页岩油资源分级评价可为油气勘探及商业开发提供技术支撑和参考依据。页岩油资源评价的关键是含油性的确定,目前常用的含油性评价方法众多,但由于陆相盆地地质条件差异巨大,评价结果具有不确定性。在对湖相页岩含油性评价的方法、模型进行系统梳理的基础上,讨论了各种含油性评价方法的优缺点,并基于现有研究成果,综合考虑含油量、可动性和地质参数间的动态耦合,提出了页岩油资源分级评价新模型。研究结果表明:①新模型以游离烃含量(S₁)、总有机碳(TOC)含量和S₁与TOC含量的比值作为分级参数,将资源分为富集资源、中等富集资源、低效资源和无效资源4级;②典型页岩盆地中的S₁随TOC含量变化的包络线呈"正态分布"特征,当TOC含量过低和过高时分别由烃源岩质量和储层物性控制着页岩油资源的富集程度;③在准噶尔盆地玛湖凹陷二叠系风城组和松辽盆地齐家—古龙凹陷白垩系青山口组,各自页岩油富集区的TOC含量上、下限分别为0.4%和2.2%以及1.5%和3.4%,页岩油有利区围绕生烃中心呈"环带状"分布。新模型的优势体现在:①考虑了烃源岩质量、储层物性以及二者在盆地尺度下的耦合关系对页岩油富集的影响;②能够从页岩含油性、可动性2个角度表征页岩油资源的富集程度。该模型的提出改变了含油量随TOC含量增大到一定值时保持恒定的认识误区,为科学评价页岩油资源量提供了依据。

关键词: 陆相页岩, 含油性, 评价方法, 资源评价, 分级评价, 富集资源