孟加拉湾深海扇石油地质特征及其勘探潜力

孟加拉湾深海扇构成了深海层序LST的主体,沉积了巨厚的第三系复合体砂体,可识别出5套层序界面。该深海扇中新统Bhuban组、渐新统Jenam组、始新统Kopili组3套烃源岩生烃期分别为早上新世(5 Ma)、渐新世末(29.3 Ma)、古近纪末(23.3 Ma)。储层以深水浊积砂岩为主,具有多期垂向叠置的沉积模式。渐新统-中新统储盖组合为最有利的储盖组合。垂向断层、不整合面、连续分布的砂体构成了良好的输导体系,其成藏模式为"下生上储型"地层或复合气藏类型。孟加拉湾深水区主要以天然气为主, 其有利勘探层系为恒河水系中上部扇带和印度东部海域中上部扇带等环孟加拉湾深水盆地第三系加积局限型水道复合体,以及中下部扇带"无底水道"附近潮道天然冲积堤砂体。 

Petroleum geologic features and exploration potentials in deep-sea fan,Bay of Bengal

The deep-sea fan of the Bay of Bengal served as the main body for the LST of deep sequence. Tertiary complex sand bodies with giant thickness deposited. 5 sequence boundaries were identified. 3 sets of source rocks in the Bhuban Formation of Miocene, the Jenam Formation of Oligocene and the Kopili Formation of Eocene gave birth to hydrocarbon during the early Pleiocene (5 Ma), the end of Oligocene (29.3 Ma) and the end of Paleogene (23.3 Ma), respectively. Deepwater turbidity sandstones worked as the main reservoir, and were featured by a depositional model of multi-period vertical overlap. Oligocene-Miocene reservoir and seal assemblage was the most favorable. Vertically, faults, unconformities and continuously-distributed sand bodies provided good pathways for petroleum migration. The possible accumulation models belong to stratigraphic reservoirs of "above-generation and below-storage" or complex ones. Natural gas is the dominant product in the deep water zone of the Bay of Bengal. Therefore, the Tertiary aggradational confined channel complexes in the deep-water basin of the Bay Rim of Bengal, such as the upper-middle deep water fans of the Ganges river system and the Indian eastern sea, as well as the natural alluvial sand embankments near to "bottomless channel" in the middle-lower deep water fans are considered as the most potential zones.