Abstract: The in-situ resources of Paleogene clastic tight oil in Jiyang depression of Bohai Bay Basin is about 20×10⁸t, mainly distributed in Member 3 and 4 of Shahejie Formation, showing great exploration potential. As controlled by the highly segmented tectonic evolution and sedimentary filling pattern of downfaulted basin, the distribution and accumulation of Paleogene clastic tight oil in Jiyang depression have unique characteristics. Through systematically summarizing the geological conditions for the formation of tight oil, and investigating the dynamic process of hydrocarbon generation and charging of source rocks and pore evolution of reservoirs, the paper makes clear the main controlling factors for the accumulation and enrichment of tight oil. The research results are as follows. (1)The widely developed organic-rich shale in the lower submember of Member 3 and upper submember of Member 4 of Shahejie Formation in Jiyang depression provides sufficient material basis for the accumulation of tight oil, and also controls the distribution of tight oil reservoirs. (2)The sandstones of various sedimentary facies adjacent to the source rocks provide reservoir spaces for tight oil. The reservoirs are characterized by low compositional maturity, complex pore throat structure, water wettability and neutral wettability, as well as high bound water content. (3)The wide developed fault system in downfaulted basin makes the source-reservoir configuration and hydrocarbon supply modes of tight oil reservoirs complex and diverse. The hydrocarbon supply modes and source-reservoir distance affect the charging and enrichment degree of tight oil reservoirs. (4)The Paleogene clastic tight oil reservoirs in Jiyang depression generally experienced two stages of accumulation, and the matching relationship between hydrocarbon accumulation dynamics and resistance controlled the oil saturation of tight oil reservoirs. Based on the above understandings, through three rounds of practical exploration, the geological-engineering integrated evaluation parameter system has been established for evaluating hydrocarbon supply conditions, reservoir quality, oil content and mobility, compressibility, and economic efficiency. According to the classification and evaluation of resources, it is found that the tight oil resources are about 7×10⁸t in the Class Ⅰ sweet spot areas including the tight conglomerate reservoir of Member 4 of Shahejie Formation in Dongying depression and the tight turbidite reservoir of Member 3 of Shahejie Formation in Huimin depression. Good exploration results have been achieved through drilling exploratory well in those areas.

Key words: Jiyang depression, downfault basin, Paleogene, tight oil, resource potential, accumulation mode

摘要： 渤海湾盆地济阳坳陷古近系碎屑岩致密油的原地资源量约为20×10⁸t,主要分布在沙河街组三段(沙三段)和沙河街组四段(沙四段),勘探潜力大。受断陷盆地强分割性的构造演化-沉积充填格局控制,济阳坳陷古近系碎屑岩致密油的分布和成藏富集具有其自身特点。通过系统梳理致密油形成的地质条件,分析烃源岩的生烃充注和储层孔隙演化的动态过程,明确了致密油成藏富集的主控因素。研究结果表明:①济阳坳陷沙三段下亚段和沙四段上亚段广泛发育的富有机质页岩为致密油的形成提供了充足的油源基础,并控制了致密油藏的分布;②邻近烃源岩发育的多种沉积成因的碎屑岩储集体为致密油提供了储集空间,储层具有成分成熟度低、孔喉结构复杂、水润湿—中性润湿、高含束缚水的特点;③断陷盆地广泛发育的断裂系统使得致密油藏的源-储配置和供烃方式复杂多样,供烃方式和源-储距离影响了致密油充注的富集程度;④济阳坳陷古近系碎屑岩致密油藏普遍发育2期成藏过程,成藏动力-阻力的匹配关系控制了致密油藏的含油饱和度。在上述认识的基础上,通过3轮勘探实践探索,建立了包括供烃条件评价、储层品质评价、含油性与可动性评价、可压性评价和经济性评价的地质—工程一体化评价参数体系。通过开展资源分级评价,落实了在东营凹陷沙四段致密砂砾岩油藏、惠民凹陷沙三段中亚段致密浊积岩油藏等Ⅰ类区致密油资源量约为7×10⁸t。Ⅰ类区部署的探井取得了良好的勘探效果。

关键词: 济阳坳陷, 断陷盆地, 古近系, 致密油, 资源潜力, 成藏模式