孟加拉盆地油气分布特征及主控因素

Hydrocarbon distribution and major controlling factors of Bengal Basin,Bangladesh

孟加拉盆地是发育在印度次大陆东北角比较典型的残留洋盆地,其经历了裂陷期、裂后期和前渊期。在残留洋盆地形成阶段发育了最重要的生储盖组合,主要烃源岩是渐新统Jenam组和中新统Bhuban组页岩;主要储集层是中新统Surma群Bhuban组和Boka Bil组陆架到潮控三角洲砂岩;盖层主要为中新统—上新统的海相页岩,分布广泛;圈闭类型以背斜为主。孟加拉盆地以天然气为主,绝大部分气田平面上分布在Surma坳陷、Tangail凸起、Hatia坳陷和东部褶皱带。天然气富集层位主要位于中新统Bhuban组和Boka Bil组。气田的分布与残留洋盆地的形成密切相关,盆地演化控制了含气层系的发育,盆地结构控制了天然气的平面分布。今后勘探的重点为盆地东部Surma坳陷及周缘、Hatia坳陷和东部褶皱带,处于压力过渡带的Surma群砂岩储层应是油气勘探的重点层系。通过对孟加拉盆地演化、石油地质条件和油气分布特征以及天然气成藏规律和主控因素的研究,可为残留洋盆地油气勘探提供借鉴和参考。

The Bengal Basin is a typical remnant ocean basin in the southeastern India subcontinent. Based on the studies of basin evolution, petroleum geology conditions and hydrocarbon distribution characteristics, the gas accumulation regularity and its main controlling factors were analyzed in order to provide references for remnant basins. The Bengal Basin underwent syn-rifting, post-rifting and foredeep episodes, and developed good source- reservoir-cap rock assemblages during the remnant ocean basin development stage. The Oligocene Jenam and Miocene Bhuban shales are the most important source rocks. The Miocene Bhuban and Boka Bil sandstones are the principle reservoir objectives, which were deposited in a tide-dominated delta to shelf environment. The seal is the widely developed Miocene-Pliocene oceanic shales . Traps are mostly anticlines. The Bengal Basin is dominated by gas, and most gas fields distribute in the Surma depression, the Tangail uplift, the Hatia depression and the eastern fold boit on the plane. Gas accumulates in the Miocene Bhuban and Boka Bil formations. Gas distribution is closely related to the formation of remnant ocean basin. The gas-bearing sequence is impacted by basin evolution and gas plane distribution is impacted by the basin framework. Gas exploration should focus on the Surma depression, the Hatia depression and the eastern fold belt in the eastern part of the basin in the near future, and the main objectives are sandstone reservoirs of the Surma Group in the pressure transition zone.