西非海岸盆地带大油气田形成条件与分布规律探析  

The forming factors and distribution rules of giant oil and gas fields in the coastal basins of West Africa

作　　者：郑应钊[1,2] 何等发[1] 马彩琴 万德辉 

机构地区：[1]中国地质大学海相储层演化与油气富集机理教育部重点实验室,北京100083 [2]长城钻探工程公司录井国际项目部,北京100101 [3]北京温菲尔德石油技术服务有限公司,北京100191

出　　处：《西北大学学报（自然科学版）》2011年第6期1018-1024,共7页Journal of Northwest University（Natural Science Edition）

基　　金：中国石油天然气股份有限公司重大科技专项基金资助项目(2008E-060903)

摘　　要：目的探究西非海岸盆地带大油气田形成条件和分布的规律,为发现更多的大油气田提供理论依据。方法从西非海岸盆地带沉积盆地分布和已发现的大油气田分布情况入手,分析其形成的有利条件,总结出西非最主要的两大含油气盆地——尼日尔三角洲盆地和下刚果盆地的含油气系统的相似性和差异性,归纳出西非大油气田形成及分布的规律。结果在西非海岸盆地带,盐岩层的发育对各盆地油气的成藏和分布有重大影响。盐岩发育的大西洋带中段,盆地油气富集程度明显高于盐岩不发育的南段、北段盆地。西非海岸盆地带的含油气系统可分为盐下、盐上两套大的含油气系统,盐下含油气系统的烃源岩是湖相页岩,储层为河流相、三角洲相、滨海相砂岩,阿普第期蒸发岩层为盖层;盐上含油气系统的烃源岩是海相页岩,储层主要为浊积岩,盖层为泥页岩。结论在西非海岸盆地带,大油气田多分布于近海或沿岸,受构造位置和沉积相带控制,形成多个油气富集带,具有垂直三角洲的沉积走向,呈带状富集的规律。由油气产出的岩性来看,其主要产出于碎屑岩储层,碳酸岩储层次之。产油层系以第三系为主,其次为白垩系。在南段盆地,形成了大气田;在中段的下刚果盆地和加蓬海岸盆地,只形成了大油田;在尼日尔三角洲盆地,形成了大油田、大气田共存的局面;西非北段盆地尚未发现大油气田。未来在西非海岸带中段盆地的深水浊积岩区有望发现更多的大油气田。Aim To study the forming factors of giant oil and gas fields in the coastal basins of West Africa, and summarize the fields＇ distribution rules in order to help the hydrocarbon exploration in the future. Methods Based on the distribution of sedimentary basins and giant oil and gas fields in West Africa Coast, the factors of its forming is analyzed, the similarity and difference of two petroleum systems in Niger delta basin and Low Congo basin is summarized and than the giant fields distribution rules are identified. Results In the coastal basins of West Africa, the deposit of salt rocks has crucial effects to the oil and gas generation, immigration, and accumulation. Basins in the middle section of the rift which deposited abundant salt rocks accumulated more hydrocarbon than that of the other sections which deposited inadequate salt rocks. The petroleum systems can be divided into the pre-sah and post-salt petroleum systems by the Aptian evaporate rock. The source rock of the pre-salt petroleum system is lacus- trine shale, the reservoir is the river, delta and shoreland sandstone, and the transitional evaporate rock is the cap rock ; the source rock of the post-salt petroleum system is marine shale, the turbidite is the major reservoir, the cap rock is shale. Conclusion The giant oil and gas fields distribute as a belt along or near the coast, the distribution are controlled by the structure position and sedimentary faces. The reservoirs are mainly Tertiary clastic rocks. Ba- sins in the southern section of the rift formed big gas fields. Basins in the middle section of the rift, such as Lower Congo basin and Gabon basin only form oil fidds, but no gas field; while Niger delta basin forms big gas fields and oil fields. In the northern section of the rift,neither big oilfield nor gas field is found. In the future, the exploration can focus on the middle section, especially on the turbidite in deep water.

关 键 词：西非 海岸盆地 大油气田 含油气系统 

分 类 号：TE122.1[石油与天然气工程—油气勘探]