海底水道体系沉积构型样式及控制因素:以尼日尔三角洲盆地陆坡区为例*
Styles of submarine-channel architecture and its controlling factors: A case study from the Niger Delta Basin slope

作为当今油气勘探开发的重要目标,海底水道的沉积构型样式复杂多变,其控制因素目前尚无定论,这大大增加了相关油气藏的钻探风险和开发难度。以尼日尔三角洲盆地陆坡区为例,以近海底高频地震信息为原型,揭示了海底水道体系的外部形态样式和内部结构样式,探究了水道体系与复合水道形态特征参数间的相互关系,分析了海底水道体系沉积构型控制因素。研究认为: (1)水道体系可分为限制性、半限制性和非限制性3个大类,限制性水道体系的边界为一明显的大型下切谷界面(或峡谷),半限制性水道体系的边界也发育明显的大型下切谷,但其界面两侧发育大型天然堤沉积,非限制性水道体系则不发育大型下切谷,其中每个大类又可依据其内部复合水道的类型,细分为2个小类(下切式和包络式)。(2)水道体系内部复合水道间存在垂向和侧向2种类型的叠置,前者可细分为孤立式、叠加式和切叠式3类,后者则包括叠合式和分离式2类。(3)地形坡度与水道体系类型和规模具有一定的耦合与关联,在类似油藏规模的局部沉积体内部,陡坡段(坡度大于1°)主要发育限制性水道体系,缓坡段(坡度0.5°~1°)主要发育半限制性水道体系,平坦段(坡度小于0.5°)主要发育非限制性水道体系;随着地形坡度的增大,水道体系的宽度减小、深度增加、宽深比减小,即向“窄深型”形态发展。该项研究不仅对深水沉积学的发展具有较大的理论意义,而且对高效开发海底水道油气藏具有重要的实际意义。

As an important target of the present-day hydrocarbon exploration and development,submarine channels have complex styles of sedimentary architecture and the associated controlling factors are still poorly understood,which significantly raises the risk of drilling of the hydrocarbon reservoirs and the difficulty of development. Taking the Niger Delta slope as an example,the present study,utilizing the high-resolution seismic data from the shallow subsurface,reveals the styles of channel-system external morphology and internal construction,probes the relationships among morphological parameters of the channel system and the channel complex,and analyzes the controlling factors of the submarine-channel sedimentary architecture. It is suggested that: (1)The channel system could be divided into three categories, i.e., confined channel system,semi-confined channel system and unconfined channel system. The boundaries of the confined and semi-confined channel system are obvious erosional surfaces and the latter commonly develops levee deposits;the unconfined channel system,however,does not have the erosional surface. In addition,each kind of the channel system could be further divided into two subgroups(the incised one and the enveloped one). (2)The channel complex within the channel system has the agrradational type as well as the accreted type;the former consists of the isolated,superposed as well as cut-and-fill group and the latter includes the cut-and-fill and detached group. (3)The slope gradient has closed relationship with the channel-system type and scale;in the reaches having steep gradients(>1°)and gentle gradients(0.5°~1°),confined channel system and semi-confined channel systems are respectively dominated,however,unconfined channel system mainly shows up in the flat section of the slope(<0.5°). With the increasing of slope gradients,the widths and heights of the channel system would respectively decrease and increase and