Abstract: The lacustrine depression basin is one type of the most important petroliferous basins in China.The terrigenous clastic sediments in the lacustrine depression basin were supplied by fluvial and alluvial fan systems around the basins.The delta system was concentrated on one depocenter or several depocenters.The lacustrine basin was alternately filed with regressive and transgressive depositional intervals.The lacustrine mudstone deposited during the maximum flooding period was the important two maximum flooding periods were the most important targets for searching the subtle traps.There were many high-order cycles of lacustrine level changes between two major maximum flooding periods.Such frequent changes of lacustrine level and sediment supply resulted in shoreline migration and delta-lobe shifting.Thus, the delta front belts became the favorable areas for searching lithologic oil reservoirs.The subtle oil reservoirs in the lacustrine depression basins were generally characterized by wide distribution,low permeability,and low richness.The high-accumulative and high-productive blocks may be formed due to matching of subtle oil reservoirs with the favorable structural settings.The oil-bearing interval of Qingshankou, Yaojia,and Nenjiang (QYN) formations in the Songliao Basin may be illustrated as one typical example of subtle oil reservoir.

Key words: lacustrine depression basins, sequence stratigraphy, mudstone, sandstone, subtle oil reservoir, Songliao Basin

摘要： 坳陷型湖盆沉积的陆源碎屑沉积物由湖盆四周的河流和冲积扇供给,三角洲沉积集中于一个或多个沉积中心.湖盆由水退与水进沉积层段交替充填.最大洪泛期沉积的湖相泥岩为坳陷型盆地重要的生油岩和区域性封盖层.2个最大洪泛期沉积的湖相泥岩所夹持的砂岩体是寻找隐蔽油气藏的最主要目标.在2个最大洪泛期之间,存在着湖平面升降变化的多次一级旋回.这种频繁的湖平面升降与沉积物供应速率的变化,导致岸线的迁移与三角洲朵叶体的摆动,使得大型三角洲前缘相带成为岩性油气藏发育的有利地区.坳陷型湖盆中发育的隐蔽油气藏,大都具有面积大、渗透率和储量丰度低的特点,但有构造背景配合,就可以形成富集高产区块.松辽盆地下白垩统青山口组、姚家组、嫩江组含油层段为这种油气藏的一个典型实例.

关键词: 坳陷型湖盆, 层序地层, 隐蔽油气藏, 松辽盆地, 勘探