准噶尔盆地南缘白垩系原油成藏特征

The Formation of Cretaceous Source Derived Oils in the Southern Junggar Basin,NW China

准噶尔盆地南缘地区的油气勘探与石油地质研究长期以来以二叠系和侏罗系含油气系统为主。本文在前人工作基础之上,从烃源岩、油源和油气运聚三方面,首次比较系统地剖析了本区的白垩系原油成藏特征。研究结果表明,白垩系烃源岩的生烃和油气聚集中心位于玛纳斯—呼图壁一带,烃源层系最大厚度可超过250m,有机质类型以Ⅰ—Ⅱ1型为主,在古近纪末进入成熟排烃阶段,是本区不可忽视的一套重要烃源岩。白垩系原油纵向上主要聚集于古近系安集海河组到白垩系吐谷鲁群储层流体系统,可能存在三期油气运聚,第一期在早更新世晚期,以流体系统内部的白垩系原油运聚成藏为主,第二期是在中更新世晚期至晚更新世早期,白垩系原油,以及成熟度相对较低的古近系原油在此流体系统内部发生混合,第三期在晚更新世末期,以油气(并以侏罗系天然气为主)在垂向上沿断层的调整为特征,最终形成了复杂的多源、多层系油气分布态势。综合认为,需要充分重视白垩系原油在本区的勘探和研究。

The petroleum geological exploration and research in the southern Junggar Basin has been focused mainly on the Permian and Jurassic petroleum systems. In this paper, we reported for the first time general features of the Cretaceous petroleum system, including source rocks, oil sources and petroleum migration/accumulation. The Cretaceous petroleum generation and accumulation center is located in the area from Manas to Hutubi, with the thickest mudstone reaching up to 250 m and best source rock whose organic matter type to Ⅰ -Ⅱ; 1. The source beds have passed into peak oil window since Paleogene. Their associated oils are occurred mainly in the reservoir sequence from Paleogene Anjihaihe Formation to Cretaceous Tugulu Group. The reservoir filling process can be divided into three stages. During the first stage in Late Pleistocene, the Cretaceous oil migrated and accumulated in the reservoir sequence. Then, during the second stage in Middle to Late Pleistocene, not only the Cretaceous oil, but also the Paleogene source derived oil participated in the migration/accumulation. During the last stage in the end of Pleistocene, the oil/gas, especially the Jurassic source derived gas, remigrated vertically along faults. This complex petroleum migration and accumulation indicates that the Cretaceous petroleum system should be placed enough emphasis in the future petroleum geological exploration and research in the southern Junggar Basin.