柴达木盆地三湖地区第四系低饱和度气层的成因机理

Origin of Low Gas-Saturated Reservoirs in the Quaternary of Sanhu Area in Qaidam Basin

低饱和度气层广泛存在于柴达木盆地三湖地区第四系,测井响应特征的模糊性和多样性使其识别比较困难。结合沉积环境、构造特征、成岩和压实作用,分别从宏观和微观两方面研究低饱和度气层的成因机理。研究表明:宏观方面,造成该区气层饱和度低的主控因素为气藏圈闭构造幅度低,其次为弱水动力沉积条件和成藏时间晚;由于纵向上沉积环境、成岩和压实作用的差异性,其形成低饱和度气层的微观机理不尽相同,但粘土矿物含量、泥质含量和地层水矿化度的'三高',碳酸盐和黄铁矿的广泛分布为其共同特征。造成浅层气层饱和度低的主控因素为泥质盖层封盖能力的微弱性,而深层气层饱和度低的主控因素则为高束缚水饱和度。

The Quaternary of Sanhu area in Qaidam basin is rich in low gas-saturated reservoirs. It is difficult to identify low gas-saturated reservoir because of the obscurities and diversities of the log response features. The authors are aiming to explore the origin of low gas-saturated reservoir from both macro and micro perspectives, after comprehensively analyzing the sedimentary environment, structural feature as well as diagenesis and compaction. With reference to this study, the low gas-saturated reservoir can be mainly attributed to the low-amplitude structural trap, and the weak hydrodynamic environment and late accumulation should be taken into consideration, as well. Due to the distinct influence of sedimentary environment, diagenesis and compaction in the vertical, the micro origins of low gas-saturated reservoir are different in the shallow and deep formation. However, the characteristics of high clay mineral content, high shale content and high formation water salinity are the same, meanwhile, the carbonate and pyrite are also widely distributed in the whole formation. In the shallow formation, the weak seal capacity of shale cap rock is the critical variation. By contrast, in the deep formation, the high irreducible water saturation should take more responsibilities.