柴达木盆地东部第四系低丰度高效气源岩地球化学特征及成藏机理

陈中红, 等，地球科学与环境学报，2007，29（1）：41-46

摘要: 对柴达木盆地东部地区第四系鸭湖和盐湖剖面进行了露头取样,并利用Rock2Eval 生油岩评价、色谱质谱等实验分析测试技术对样品进行了地球化学特征分析。实验结果表明,样品有机碳含量变化不大, w ( TOC)为0. 15 %～0. 75 % ,w (S1 + S2 ) 为(0. 24～2. 5) ×10 - 3 。第四系气源岩中的有机质类型多以Ⅲ型有机质为主,少数为Ⅱ型,极少数为Ⅰ型。有机质主要来源于陆源生物为主的腐殖型和含腐泥腐殖型,是典型的低丰度有机质气源岩。C29甾烷异构化参数C29αββ/ (αββ+ααα) 、C29ααα20S/ (20S + 20R) 分布分别为0. 34～0. 38 、0. 27～0. 33 ,C31升藿烷22S/ (22S + 22R) 分布为0. 49～0. 56 ,显示第四系样品多处于未熟状态。巨厚的气源岩沉积厚度、第四纪寒冷的气候和高盐度的水体环境及有效的生储盖组合是形成第四系大型生物气藏的有利条件。

关键词: 第四系; 气源岩; 地球化学; 生物标志化合物; 柴达木盆地

中图分类号: P618. 130. 1 ; TE122. 113 　文献标志码: A 　文章编号: 167226561 (2007) 0120041206

Characteristics and Hydrocarbon-Accumulation Mechanism of Source Rocks with Low Abundance and High Eff iciency in Quaternary Period of Eastern Qaidam Basin

CHEN Zhong-hong , et al，Journal of Earth Sciences and Environment, 2007，29（1）：41-46

( School of Earth Resource and I nf ormation , China Universi t y of Pet roleum , Dongy ing 257061 , S handong , China)

Abstract : In order to investigate the characteristics and hydrocarbon accumulation mechanism of source rocks with low abundance and high efficiency in the Quaternary in the eastern Qaidam basin , the rock samples selected from the outcrop of Quaternary were analyzed , including the organic carbon content , the parameters of pyrolysis and biomarker characters of saturated hydrocarbon by means of Rock-Eval , GC2MS and so on. The result s show that the content of organic carbon ranges from 0. 15 % to 0.75 % , and the value of S1 + S2 ranges f rom 0.25 mg/ g to 2.5 mg/g, which displays it s limited hydrocarbon2generating potential. There were mainly type Ⅲof kerogen , a few of typeⅡof kerogen , and few of type Ⅰof kerogen. There was predominance of phytane to pristane , and the ratio of pristane to phytane was lowerer than 0. 5. The values of the parameters of C29αββ/ (αββ+ααα) and C29ααα20S/ (20S + 20R) were 0. 34～0. 38 and 0. 27～0. 33 , and the organic matter was being in the stage of low maturity. The water temperature of the depositional lake was low and it s salinity was high. The unique depositional environment s of this area in the Quaternary are the important conditions for forming the large scale biogenic gas pools. The water environment with a high salinity slowed down the degradation rate of the organic matter . The methane bacteria activity was rest rained in cold environment for a long time and the generation peak of the biogenic gas was delayed. Moreover, the massive Quaternary dark mudstone and f requent developedsandstone in Sanhu area provide abundant gas source and constitute a favorable combination of reservoir.

Key words : Quaternary System; gas source rocks ; geochemist ry ; biomarker ; Qaidam basin

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