鄂尔多斯盆地东缘临兴地区天然气成因类型及气源分析

Genetic Types and Sources of Natural Gas in Linxing Area,the Eastern Margin of Ordos Basin,China

鄂尔多斯盆地东缘临兴地区致密砂岩气勘探程度低,对其天然气地球化学特征及天然气源岩的认识较为局限。通过对天然气组分和碳同位素特征分析,利用生烃动力学实验计算煤岩、碳质泥岩、暗色泥岩3类烃源岩生烃强度,结合3类烃源岩生烃潜力,建立天然气源岩生气贡献率计算模型。结果表明:临兴地区烃源岩母质类型以Ⅲ型、Ⅱ2型干酪根为主,有机质丰度高,全区烃源岩大都处于热演化成熟阶段;天然气碳同位素值较重,显示出煤型气特征;天然气碳同位素值在纵向运移过程中未发生分异作用,在平面比值变化上未发生倒转,表现出近源、持续充注的特点;天然气主要来源于本溪组—太原组煤岩,其生气贡献率分别为43.3%、43.8%;天然气与烃源岩具有良好的垂向关系,有效烃源岩区可在一定程度上控制临兴地区天然气有利区的勘探。

The exploration level of tight sandstone gas is low in Linxing area,the eastern margin of Ordos Basin,China,and the cognitions of geochemical characteristics and source rocks of natural gas are relatively limited.The natural gas components and carbon isotope characteristics were analyzed;the hydrocarbon generating intensities of coal rock,carbonaceous mudstone and dark mudstone were calculated by using the experiment of hydrocarbon generation kinetics;combined with the hydrocarbon generation potential of three source rocks,the calculation model for natural gas generation contribution rate of source rocks was established.The results show that the main parent material types of source rocks areⅢ-type andⅡ2-type kerogens,the organic matter has high abundance,and the source rocks are mostly in the stage of thermal maturation;the carbon isotope values of natural gas are relatively heavy,and show the characteristics of coal-type gas;the carbon isotope values of natural gas have no differentiation in the process of vertical migration,and also no inversion in the change of plane ratio,indicating the characteristics of near source and continuous injection;the natural gas mainly derives from the coal rocks of Benxi Formation-Taiyuan Formation,and the gas generation contribution rates are 43.3%and 43.8%,respectively;the natural gas has a good vertical matching relationship with source rocks,and the effective source rocks control the exploration of favorable areas of natural gas in Linxing area.