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

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