准噶尔盆地东部石炭系天然气地球化学特征及成因

Geochemical Characteristics and the Origin of Natural Gas in Carboniferous,Eastern Junggar Basin

准噶尔盆地东部石炭系"自生自储"型油气藏具有多凹陷多套烃源岩晚期成藏特征,通过对准东地区石炭系天然气组成、同位素特征进行分析,研究石炭系天然气成因特征,追溯其源岩有机质类型和同位素范围,并结合石炭系烃源岩特征进行气源对比。准东地区石炭系所有天然气样品均为煤型气,陆东地区大部分表现为干气;而五彩湾地区天然气所有样品为湿气,部分样品表现为凝析油伴生气。陆东与五彩湾地区烷烃气碳同位素大多呈正序列分布,且乙烷碳同位素组成普遍偏重,但五彩湾地区天然气碳同位素组成均轻于陆东地区。滴水泉组和巴山组2套烃源岩有机质类型和时空分布差异性造成了陆东与五彩湾地区天然气组分和同位素组成明显不同,早石炭世仅在五彩湾地区发育局限海相环境的滴水泉组烃源岩,而巴山组烃源岩则发育于中晚石炭世火山活动间歇期,其广泛分布于准东地区各个陆内裂陷,陆东地区天然气主要来源于滴水泉凹陷的巴山组烃源岩,而五彩湾地区天然气则为五彩湾凹陷内滴水泉组和巴山组2套烃源岩混合来源。

The Carboniferous'self-generation and self-preservation'gas in eastern Junggar Basin was characterized by late accumulation from multiple sets of source rocks and depressions.The analyses of gas composition and isotopes were performed to trace the isotopic and organic facies of the possible source rocks,and to determine the origin of natural gas in Carboniferous,as well as gas-source correlation in eastern Junggar Basin.All the gas samples from Ludong area are coal-derived gas,and most of them are dry gas,while the gas samples from Wucaiwan area are mixed gas,mixing of coal-derived gas and condensate associated gas,belonging to wet gas.The carbon isotopic distribution of most samples from both Ludong and Wucaiwan is characterized by positive carbon sequence among C_1,C_2,C_3 and C_4 alkanes.The carbon isotopes for samples from Ludong area are heavier than samples from Wucanwan area,and carbon isotope of ethane is generally enriched in ^(13)C.The differences of organic matter types and the temporal and spatial distributions between Dishuiquan Formation in Lower Carboniferous and Batamayineishan Formation in Upper Carboninerous in the eastern Junggar Basin caused the samples from Wucaiwan area with lighter carbon isotope and condensate associated gas.The source rocks of Dishuiquan Formation deposited in restricted sea were only developed in Wucaiwan area during the Early Carboniferous,and the source rocks from Batamayineishan Formation were characterized by salty water lake,which were widely distributed in the various continental faulted depression in Ludong and Wucaiwan area.Hence,gases in Ludong area are mainly from Batamayineishan Formation in Dishuiquan Sag,while gases for Wucanwan area are from Batamayineishan Formation and Dishuiquan Formation in Wucaiwan Sag.