鄂尔多斯盆地临兴地区上古生界天然气成因及来源

Origin and source of natural gas in the Upper Paleozoic in Linxing area,Ordos Basin

天然气成因及来源研究对天然气勘探开发具有重要作用,可以为天然气的运移成藏提供理论依据。通过对鄂尔多斯盆地临兴地区上古生界天然气组分、碳同位素、轻烃及烃源岩等特征进行综合分析研究,探讨该区上古生界天然气成因及来源。结果表明:临兴地区上古生界天然气组分含量以甲烷为主,重烃和非烃含量较低,主要属于干气;天然气δ^13C1值、δ^13C2值和δ^13C3值分别介于-45.6‰^-32.9‰、-28.9‰^-22.3‰和-26.2‰^-19.1‰之间,总体表现出正碳序列变化趋势,并且δ^13C1值均小于-30‰,具有典型的有机成因气特征。轻烃组成特征上具有一定的相似性,C7系列表现出甲基环己烷优势;C5-7系列主要表现出异构烷烃优势。该区上古生界天然气主要属于成熟煤成气,含有少量煤成气与油型气的混合气;石盒子组天然气藏主要是由山西组烃源岩生烃增压扩散运移至近源或远源储层内充注成藏;太原组天然气藏主要来自于太原组自身的烃源岩,在源岩内自生自储成藏。

Study of the origin and source of natural gas plays an important role in exploration and development,which can provide a theoretical basis for natural gas migration and accumulation. Based on the comprehensive analysis of the characteristics of the natural gas composition,carbon isotope,light hydrocarbons and source rocks in the Upper Paleozoic in Linxing area of Ordos Basin,the origin and source of Upper Paleozoic natural gas in this area are discussed. The study shows that methane is the main component of natural gas,with low contents of heavy hydrocarbons and non-hydrocarbons,mainly belonging to dry gas in the Upper Paleozoic in Linxing area. The values of δ^13C1,δ^13C2 and δ^13C3 of natural gas are in the ranges from-45.6‰ to-32.9‰,-28.9‰ to-22.3‰ and-26.2‰ to-19.1‰,respectively. The carbon isotopic values of alkane gas show a general trend of positive carbon sequence. δ^13C1 value is less than-30‰,with typical characteristics of organic origin. There is a certain similarity in the composition characteristics of light hydrocarbons. The C7 series shows an advantage of methyl hexane,while the C5-7 series mainly shows an advantage of isoalkane. The Upper Paleozoic natural gas in this area is mainly composed of mature coal-derived gas,containing a small amount of coalderived gas and oil-type gas mixture;the natural gas reservoirs of Shihezi Formation are mainly transported by pressurized diffusion of hydrocarbon generation from Shanxi Formation source rock hydrocarbons to filling and accumulation in near-source reservoir or far-source reservoir. The natural gas reservoirs of Taiyuan Formation mainly come from the source rocks of Taiyuan Formation itself,and are generated and stored in the source rocks,in which it is self-generation and self-preservation.