Characteristics and Generation-Evolution Model of Marine Biogas in the Yinggehai Basin
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摘要: 莺歌海盆地浅层第四系-上新统存在丰富的生物气资源,已发现生物气的组成以甲烷和氮为主、干燥系数高达0.99,甲烷碳同位素轻(-65.57‰~-63.14‰)尤其是氢同位素偏重(-172.1‰~-108.5‰)是该区生物气的重要特点.研究表明,该区第四系-上新统海相沉积有机质是生物气的基质,这套源岩的平均有机碳含量约0.4%,有机质中细菌可利用基质以粗纤维、半纤维素和蛋白质为主,特别是有机质生化代谢过程中的中间产物-氨基酸、乙酸含量异常高,揭示其正处在活跃的生化成气时期;根据模拟实验结果结合本区的地质条件,初步确定生物气生成的主带在35~65℃之间、生化成气下限深度约为85℃(对应井深约2000 m,实际埋深1900 m左右),进而建立了海相生物气的形成演化模式。Abstract: There is great biogas potential in the Guaternary and Pliocene of the Yinggehai Basin. The compositions of gases f ound in the Basin are mainly methane and nitrogen. These biogases are characterized by high dry coefficients(C1/C1-5ratio)of 0.99, light carbon isotopes of methane(-65.57 %!-63.14 %), especially heavy hydrogen isotopic values("Dc1%)of -172. 1 %!-108. 5 %. Geochemical data show that the Guaternary and Pliocene mud has the meanTOC value of 0.4 % and contains abundant organic matter which can be degraded by bacteria. The organic matter mainly consists of coarse-fi ber,semi-fiber and protein.Noticeably,it contains a high content of amino acid that is an inter mediate product during the f or mation process of biogas. This indicates that the mudstone in the Guaternary and Pliocene of the Basin is f avourable to biogas f or mation and is good biogas sourcerock.The data of modeling eXperi ment,combined with the gas measurement log and geotemperat ure gradient data of the basin,can be used to predict that the main stage of bio-gas generation is bet ween 35 C and 65 C and the death temperat ure of bio-gases is about 85 C(eCuivalent with the burial depth of around 1 900 min the Basin).Finally,we suggest the generation-evolution model of marine biogas in the Yinggehai basin.
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