渤海湾盆地不同凹陷新近系油气成藏条件差异性及聚集模式

Difference of reservoir forming conditions of different depressions and accumulation models of Neogene hydrocarbon in Bohai Bay Basin

通过对渤海湾盆地新近系生储盖、圈闭及输导等条件的研究,探讨不同凹陷新近系油气成藏条件的差异,并建立3类油气聚集模式。研究表明:渤海湾盆地新近系油气成藏具有它源供烃、储层发育、断层输导和晚期成藏等共性,但不同凹陷的成藏条件差异较大;自盆地外围凹陷向渤中凹陷,新近系的供烃层系变多变新,新烃源岩层的贡献逐渐增大,盖层质量逐渐变好,新近系油气输导方式主要有通源断层直达、次级断层调整和混合输导式3种;油气聚集模式概括为'原生供烃-通源断裂输导-构造控圈'披覆带聚集模式、'次生供烃-浅部断裂输导-断层控圈'浅凹带聚集模式及'混合供烃-复式输导-不整合控圈'斜坡带聚集模式3类;披覆带模式成藏条件最优越,适于新近系大规模油气聚集,而分别受保存条件、输导条件制约的斜坡带、浅凹带聚集模式,新近系油气相对不甚富集。

Based on the study of source-reservoir-cap rock, trap, and transportation conditions of Neogene in Bohai Bay Ba-sin, we discussed the accumulation conditions in different depressions, and established three hydrocarbon accumulation mod-els. The study shows that it is common in the Neogene, Bohai Bay Basin： the hydrocarbon was mainly provided by the heter-ogeneous source rocks; the reservoir rocks developed well; fault was the migration pathway; hydrocarbon acculmulation timewas late; and different depressions provided different hydrocarbon accumulation conditions. From the peripheral depressionsto Bozhong depression, the source rock layers for the Neogene hydrocarbon become newer. The contribution of the new sourcerocks increases and the quality of the cap rock becomes better. Three modes of hydrocarbon migration were proposed, namelydirect migration through source faults,secondary faults adjustment migration and mixed transportation. These models can besummarized as： “source rock supply hydrocarbon-transported by source faults-trapped by structural features”model in thedrape structural belt, “secondary source supply hydrocarbon -transported by shallow faults-trapped by faults” model in theshallow concave belt, and “mixed sources for hydrocarbon-multiple migration ways-trapped by unconformity” model in theslope belt. The drape structural belt model is in favor of accumulating bulk Neogene hydrocarbon due to its corking accumula-tion conditions, while the shallow concave belt model and the slope belt model limited by the preservation and migration con-ditions are relatively less enriched in hydrocarbon.