鄂尔多斯盆地东部上古生界不同含气组合天然气地球化学特征

通过对鄂尔多斯盆地东部上古生界110个天然气样品组分及碳同位素的分析,认为下部含气组合本溪组、太原组及山西组气藏以干气为主,具有甲烷含量高、重烃低、干燥系数大、非烃略高的特点;中部含气组合盒8气藏以湿气为主,干气为辅,干燥系数具有2个主峰(0.93～0.94,0.98～0.99),重烃含量较高,非烃含量低;上部含气组合千5气藏天然气甲烷含量最高,重烃含量略低,干燥系数为0.96～0.99,非烃含量最低。不同含气组合中甲烷碳同位素值比较重,乙烷、丙烷碳同位素具有典型的煤成气的特点。烃源岩干酪根碳同位素、烃源岩及盖层中脱附烃组分均表明,气源岩具有典型的煤系烃源岩的特征,不同含气组合中的天然气来自下伏煤系气源岩。 

Geochemical characteristics of natural gas of different gas-bearing assemblages in Upper Paleozoic, eastern Ordos Basin

Based on gas molecular and stable carbon isotope analyses of 110 gas samples collected from the Upper Paleozoic in the eastern Ordos Basin,it has been concluded that the lower gas-bearing assemblages such as the Benxi,Taiyuan and Shanxi Formations mainly contain dry gas characterized by high methane content,low C2+ alkanes content,high dryness and relatively high non-hydrocarbon content.The He8 gas pools of the middle gas-bearing assemblages mainly contain wet gas characterized by 2 peaks for dryness(0.93-0.94,0.98-0.99) as well as high C2+ alkanes content and low non-hydrocarbon content.The Qian5 gas pools of the upper gas-bearing assemblages are characterized by the highest methane content,relatively lower C2+ alkanes content,the lowest non-hydrocarbon content and the dryness ranges from 0.96 to 0.99.Carbon isotope values of methane are heavy among different gas-bearing assemblages and those of ethane and propane are in accordance with typical coal gas.Carbon isotopes of kerogen,desorption hydrocarbons of source rocks and cap rocks indicate that the source rocks have the characteristics of typical coal source rocks.Natural gas of different gas-bearing assemblages generates from underlying humic sources.