西南非海岸盆地烃源岩研究新认识及勘探意义

New findings from the study on source rock of Southwest Africa Coastal Basin and its significance to exploration

位于非洲大陆西海岸最南端的西南非海岸盆地自20世纪70年代勘探至今,尚未取得大的油气勘探突破,而同位于西海岸的宽扎、下刚果-刚果扇、加蓬盆地均获得了大量的油气发现。为厘清该盆地勘探潜力,本文以烃源岩研究为核心,综合利用地化、古生物、钻井、地震等相关资料,对该盆地主力烃源岩—过渡期海相烃源岩进行综合有机相分析,明确该盆地主力烃源岩从陆向海呈现“内带倾气、外带倾油”的特点。随后,综合盆地构造发育背景、沉积储层展布特征、油气成藏规律,指出该盆地整体可能发育4个潜在有利勘探区带,即威尔维斯次盆深水区斜坡扇石油勘探潜力区带、威尔维斯次盆陆架边缘礁滩相碳酸盐岩石油勘探潜力区带、奥兰治次盆碳酸盐岩台地生物礁相石油勘探潜力区带、奥兰治次盆风成砂天然气勘探潜力区带,为该盆地下一步勘探指明了方向。

Southwest African Coastal Basin,located at the southernmost end of the west coast of African continent,has not been made any breakthrough since exploration in the 1970 s.Yet a large number of oil and gas discoveries have been made in Kwanza,Lower Congo-Congo Fan and Gabon basins,which are also located at the west coast of African continent.In order to clarify the exploration potential of the Southwest African Coastal Basin,the source rock of the basin is taken as the study object to comprehensively analyze the characteristic of sedimentary organic facies of its main source rock,i.e.,the marine source rock of the transitional period based on the available data such as geochemical,paleontological,drilling,and seismic data.According to the analysis results,it is clear that the main source rock in the basin has the characteristics of gas bearing in the inner zone and oil bearing in the outer zone from land facies to marine facies.Subsequently,based on the basin tectonic background,sediments and reservoir distribution and hydrocarbon accumulation law,it is determined that the basin has 4 potential favorable exploration zones,i.e.,the slope fan potential oil exploration zone in deepwater area of Walvis sub-basin,the reef flat facies carbonate potential oil exploration zone in shelf margin of Walvis sub-basin,the biohermal facies potential oil exploration zone in carbonate platform of Orange sub-basin,and the aeolian sand potential gas exploration zone in Orange sub-basin,which highlights the direction of further exploration in the basin.