我国海相地层膏盐岩盖层分布与近期油气勘探方向

Distribution of gypsum-salt cap rocks and near-term hydrocarbon exploration targets in the marine sequences of China

以"勘探反演"的思路,总结了近年来膏盐岩下油气勘探研究的现状,分析了膏盐岩盖层的分布特点,讨论了我国膏盐岩下海相地层的勘探潜力与方向。研究认为,膏盐岩是优质盖层,在我国四川和塔里木两大盆地的海相地层中分布广泛;膏盐岩下油气资源潜力大,是我国未来油气勘探的重点领域。在南方地区,除白垩-古近系外,膏盐岩盖层分布的层位主要有中-下寒武统和中-下三叠统。膏盐岩盖层平面上分布范围很广,但不同地区分布差异性大。其中,中-下三叠统膏盐岩盖层与四川盆地油气分布关系密切;寒武系和中-下三叠统膏盐岩盖层较厚,对海相油气的封盖能力最强。石炭系在湖南中部地区已有一定范围分布。塔里木盆地也发现和落实了多套膏盐岩盖层。在塔里木台盆区最主要的盖层有两套,即寒武系膏盐岩层和石炭系中上部膏盐泥岩层,同样显示出优越的封盖条件。特别是石炭系,是塔里木台盆区最主要的区域性盖层;寒武系膏盐岩盖层在巴楚-麦盖提地区分布面积广,连续厚度大。综合考虑膏盐岩下油气成藏的地质条件,特别是斜坡带、枢纽带的控油气作用,提出了南方和塔里木盆地2个地区5个领域或区带为近期有利勘探区。其中,四川盆地3个领域或区带,分别是三叠系膏盐岩下镇巴区带、寒武系膏盐岩下川南区带和寒武系膏盐岩下鄂西渝东区带;塔里木盆地两个领域或区带,分别是寒武系膏盐岩下巴-麦区带和石炭系膏盐岩下勘探有利区带。

Through reverse thinking,we summarize the status of research in the field of subsalt hydrocarbon exploration,analyze the distribution characteristics for gypsum-salt cap rocks,and discuss the potentiality and targets of subsalt hydrocarbon exploration within marine seuences in china.Gypsum and salt are excellent cap rocks which widely occur in the marine sequences of Tarim and Sichuan basins.Subsalt reservoirs are large in resource volume and are the main targets of future exploration.In southern China,gypsum-salt cap rocks mainly occur in the Lower-Middle Cambrian and Lower-Middle Triassic,in addition to the Cretaceous and Paleogene.The gypsum-salt cap rocks are extensive in lateral distribution but large in differences in different areas.For example,the Lower-Middle Triassic gypsum-salt cap rocks are closely related to hydrocarbon distribution in Sichuan Basin.The Cambrian and Lower-Middle Triassic gypsum-salt cap rocks are relatively thick and are the best seals for the marine reservoirs.The Carboniferous gypsum-salt cap rocks also occur in central Hunan province.Moreover,se-veral gypsum-salt cap rocks also exist in Tarim Basin.For the Tarim platform-basin area,there are two sets of major cap rocks,i.e.the Cambrian and the middle-upper Carboniferous gypsum-salt cap rocks,especially the former is the major regional seal.The Cambrian gypsum-salt cap rocks in Bachu-Maigaiti area are large in both areal distribution and continuous thickness.Taking the overall geologic conditions for hydrocarbon accumulation in subsalt area into account,especially the controlling factors of slope and hinge zone for hydrocarbon accumulation,the paper suggest five plays or fields as the major targets of near-term exploration in southern China and Tarim Basin.