中亚主要含盐盆地油气成藏特征及其富集主控因素

Hydrocarbon accumulation characteristics and main controlling factors of major salt-bearing basins in Central Asia

  • 摘要: 中亚地区阿姆河盆地和滨里海盆地油气资源潜力巨大,是中亚盆地中最具代表性的含盐盆地。基于最新的油气地质资料,对阿姆河盆地和滨里海盆地的构造沉积演化、石油地质特征和油气分布规律进行了系统对比, 深入探讨了影响含盐盆地油气分布的主控因素,从而加深对中亚地区区域性油气分布规律的认识。尽管阿姆河盆地和滨里海盆地是在不同地质背景下形成的富油气盆地,二者的构造演化过程、沉积地层和油气地质特征存在明显差异,但盆地的盐下均发育了形成于同裂谷期—拗陷期的优质烃源岩,具有厚度巨大、有机质丰度高、热演化程度高等特征。阿姆河盆地和滨里海盆地内广泛发育的含盐层系控制了这两大盆地的油气时空分布,这套含盐层系将盆地划分为盐上和盐下2套油气成藏组合。其中,油气主要富集于阿姆河盆地盐下卡洛夫—牛津阶碳酸盐岩成藏组合和滨里海盆地盐下石炭系—下二叠统碳酸盐岩成藏组合。膏盐岩盖层具有良好的封堵性能,与盐下古隆起构造部位的有利储集相带构成了大型油气田形成的有利条件。此外,深大断裂、膏盐岩尖灭带和盐构造活动形成的盐窗为盐下烃源岩油气的垂向运移提供了运移通道,这些因素是盐上能否形成油气规模聚集的关键。

     

    Abstract: The Amu Darya Basin and the Pre-Caspian Basin in Central Asia hold enormous hydrocarbon resource potential and are the most representative salt-bearing basins in the region. Based on the latest petroleum geological data, this study systematically compares the structural and sedimentary evolution, petroleum geological characteristics, and hydrocarbon distribution patterns of the basins. The main factors controlling hydrocarbon distribution in salt-bearing basins are thoroughly analyzed to deepen the understanding of regional hydrocarbon accumulation patterns in Central Asia. Since the Amu Darya Basin and the Pre-Caspian Basin are oil and gas-rich basins formed under different geological backgrounds, there are obvious differences in the tectonic evolution process, sedimentary strata and oil and gas geological characteristics of the two; however, the pre-salt basins have developed high-quality source rocks formed in the same rift period and depression period, with the characteristics of huge thickness, high organic matter abundance and high degree of thermal evolution. The extensive development of salt-bearing strata in the Amu Darya Basin and the Pre-Caspian Basin controls the spatial and temporal distribution of hydrocarbons. This salt-bearing system divides the basins into two hydrocarbon accumulation systems: sub-salt and supra-salt rock sequences. Hydrocarbons are mainly concentrated in the sub-salt Callovian to Oxfordian carbonate reservoirs in the Amu Darya Basin and in the sub-salt Carboniferous to Lower Permian carbonate reservoirs in the Pre-Caspian Basin. Gypsum-salt cap rocks exhibit excellent sealing properties and, in conjunction with favorable reservoir facies in the structural positions of the paleo-uplift of the sub-salt rock sequences, provide optimal conditions for forming large oil and gas fields. Additionally, salt windows induced by deep faults, gypsum-salt pinch-out zones, and salt tectonic activities facilitate vertical migration of hydrocarbons in sub-salt source rocks, playing a crucial role in large-scale hydrocarbon accumulation in supra-salt rock sequences.

     

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