准噶尔盆地新光地区佳木河组天然气地球化学特征及成因

通过对二叠系烃源岩生烃潜力评价及地层孔隙生烃模拟实验，明确了准噶尔盆地二叠系佳木河组、风城组和下乌尔禾组3套烃源岩生烃潜力及生烃特征，并在天然气地球化学特征研究基础上，结合与天然气伴生凝析油正构烷烃碳同位素分析，确定了准噶尔盆地中拐凸起新光地区佳木河组致密砂岩气藏天然气的来源。结果表明，二叠系3套烃源岩生烃潜力从大到小顺序为：风城组＞下乌尔禾组＞佳木河组，风城组烃源岩类型最好，以生油为主，下乌尔禾组烃源岩倾油倾气，佳木河组烃源岩倾气。新光地区佳木河组致密砂岩油藏天然气C₇轻烃组成以正庚烷为主，含量大于40%，甲基环己烷含量小于40%，乙烷碳同位素值分布在-29.0‰~-27.0‰之间，为偏腐泥型的过渡型气；与佳木河组致密砂岩天然气伴生的凝析油正构烷烃碳同位素增加呈“V”型分布，与下乌尔禾组烃源岩相一致，表明新光地区佳木河组凝析油来源于下乌尔禾组烃源岩。综合分析认为，准噶尔盆地新光地区佳木河组致密砂岩天然气主要来源于高成熟的下乌尔禾组烃源岩。

Geochemical characteristics and genesis of natural gas in Jiamuhe Formation in Xinguang area,Junggar Basin

In this paper, the hydrocarbon generation potential and characteristics of the three sets of source rocks of the Jiamuhe, the Fengcheng and the Lower Wuerhe Formations in the Junggar Basin are identified by the hydrocarbon generation potential evaluation and the formation porosity thermocompression simulation experiment. Furthermore, based on the study of natural gas geochemical characteristics, combined with the carbon isotope analysis of natural gas associated condensate normal alkanes, the source of natural gas in the Jiamuhe Formation tight sandstone reservoir in the Xinguang area of the Zhongguai Uplift in the Junggar Basin was determined. The result shows, hydrocarbon generation potential of the three sets of source rocks in the Permian: Fengcheng Formation > Lower Wuerhe Formation > Jiamuhe Formation. Fengcheng Formation source rocks are the best, but mainly generate oil, the Lower Wuerhe Formation source rocks generate oil and gas, Jiamuhe Formation source rocks only generate gas. The C₇ light hydrocarbon compositions of the natural sandstone reservoir of the Jiamuhe Formation in Xinguang area is dominated by n-heptane, with content more than 40%, the methylcyclohexane content less than 40%, and the carbon isotope distribution of ethane between -29.0‰ and -27.0‰, which shows the gas are from sapropelic source rock. The carbon isotope composition distribution of n-alkanes in the condensate oil associated with the tight sandstone natural gas of the Jiamuhe Formation demonstrates “V” type, which is consistent with the source rocks of the Lower Wuerhe Formation, indicating that the Jiamuhe Formation condensate from the Xinguang area is derived from the Lower Wuerhe Formation source rock. According to the comprehensive analysis, the tight sandstone natural gas of the Jiamuhe Formation in the Xinguang area of the Junggar Basin is mainly derived from the high-mature Lower Wuerhe Formation source rocks.