深水沉积差异及其对油气分布影响

尼日尔三角洲盆地深水油气资源丰富，其中盆地东部深水区已发现的亿顿级油气田数量和累计油气可采储量均约为西部深水区的两倍，东、西部深水区油气差异巨大，开展尼日尔三角洲盆地深水沉积特征和差异研究具有重要的生产意义和学术价值。通过对该盆地大量地震、测井和岩心等资料的分析，提出了西部深水扇主要是由三角洲提供物源，通过大型峡谷的运输，在深水平原区形成树枝状发散的深水扇，又称作“有根深水扇”；东部深水扇也是由三角洲供源，但由于缺乏大型峡谷的运输，沉积物沿大陆斜坡滑移至半深海—深海平原，形成根部不发育的“扇面状”深水扇，又称作“无根深水扇”。尼日尔三角洲盆地东西部深水区油气分布差异，除构造等因素外，其最主要的原因为有/无峡谷作为物源运输通道，分别形成的不同沉积类型，进而分别形成两种样式的深水圈闭类型，最终造成东西部深水区油气分布的巨大差异。

Influence of Different Modes of Deep-water Sedimentation on Oil and Gas Distribution: A case study of deep-water fans in eastern and western Niger Delta Basin

The Niger Delta Basin is rich in deep-water oil and gas reserves. However， both the number of plays at billion level and the total recoverable reserves in the eastern areas are double those in the western areas， which represents a huge distinction. Therefore， studies of their characteristics and differences have particular value， both industrial and theoretical. Based on the analysis of a large quantity of seismic， well-log and core data for the basin， it is proposed that the deep-water fan in the western region is mainly sourced from the delta， forming a deep-water fan with branches （‘rooted deep-water fan’） on the deep-water abyssal plain as a result of transporting large-scale canyons. The eastern deep-water fan is also sourced from the delta， but due to the lack of large-scale canyons， the source material slid down the continental slope from the bathyal zone to the abyssal plain， forming a fan-shaped deposit without a deep root （‘rootless deep-water fan’）. This type of fan has a short transportation distance and is mainly composed of lobes and channelized lobes； mudstone diapirs and thrust nappes form structural lithological traps with large filling areas and thick reservoirs. In summary， the main reason for the different oil and gas distributios in the eastern and western deep-water areas of the Niger Delta Basin， apart from structural factors， is whether or not a canyon was the conduit for transporting the material from the source. Different sedimentary types correspondingly formed in the eastern and western regions and the two kinds of deep-water traps developed.