西非被动大陆边缘盆地盐构造对油气的控制作用

Control of salt structures on hydrocarbons in the passive continental margin of West Africa

西非被动大陆边缘盐盆地是目前世界油气勘探的重点和热点地区,近年来该区发现的油气与盐构造密切相关。西非被动大陆边缘盐盆地主要集中于安哥拉—喀麦隆段,普遍发育厚层盐层,厚度最大可达1500m,分布范围平均宽度约300km。盐盆地的发育具有明显的分段性,横向上可以将盐盆地划分为坡上伸展区和坡下挤压区。伸展区又可以细分为坡上构造带、生长断层带以及底辟构造带,以发育掀斜地块、滚动构造和龟背斜构造为特征,宽约100～150km;挤压区主要发育盐席、盐舌、逆冲断层和短波褶皱,宽为100～200km。伸展区和挤压区都具有良好的勘探前景,伸展区油气储量比挤压区略大。与盐构造相关的圈闭包括拱形圈闭、盐刺穿侧向封堵和断层遮挡圈闭、不整合圈闭、构造-岩性圈闭等,其中拱形圈闭是非洲西部最有潜力的圈闭。

Salt basins along the passive continental margin of West Africa are becoming one of the most attractive areas for hydrocarbon exploration.The oil and gas discovered recently are related to salt structures.The salt structures are widespread in Anglo-Cameroon,the thickness of salt is up to 1 500 m and the average width is 300 km.These basins can be divided into two parts in horizontal direction：extensional zone and compressional zone,which extend 100-150 km and 100-200 km respectively.The extensional zone includes sealed titled zone,growth fault zone and diapir zone,and is characterized by tilted block,rollover structure and turtle structure anticline.The compressional zone is characterized by salt sheet,salt tongue,thrust fault and small folds.Oil and gas are distributed in both the zones,oil and gas reserves in the extensional zone are a little more than those in the compressional zone.Several types of salt related traps can be recognized,such as salt anticline,salt diapir and fault related trap,unconformity and structural-lithologic traps.Salt anticlines are the most potential exploration targets.