关键词: 坳陷型湖盆, 层序地层, 隐蔽油气藏, 松辽盆地, 勘探

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