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塔里木盆地塔中地区奥陶系天然气烃类气体以甲烷为主,含量主要分布在75%~95%之间,重烃(C2+)含量低,为3%~7%,干燥系数介于0.73~0.99之间;非烃气体以N2和CO2为主,具高N2、低CO2特征,含量分别为4%~8%和2%~6%。天然气δ13C1值为-63.1‰~-37.7‰,δ13C2值为-40.6‰~-24.8‰。天然气在平面上存在较明显差异,Ⅰ号带东段天然气干燥系数高,N2含量高、CO2含量低,δ13C1值较低,以热裂解成因为主;Ⅰ号带西段干燥系数偏低,N2含量低、CO2含量较高,δ13C1值较高,以热解成因的伴生气与混合成因气为主;Ⅰ号带中段及主垒带卡1区天然气δ13C1值介于两者之间,但前者天然气组分变化比较大,以原油伴生气和腐泥型有机质热解生成的干气为主,而后者天然气干燥系数变化较大,以热解生成的原油伴生气为主。天然气性质上的区带性差别可能与断裂及裂缝的发育程度有关,天然气成藏受喜马拉雅期构造运动的影响,以晚期成藏为主。
The Ordovician natural gas in Tazhong area of Tarim Basin is dominated by methane. The content of hydrocarbon is mainly between 75% and 95%. The content of heavy hydrocarbon (C2 +) is 3% ~ 7% and the drying coefficient is between 0.73 ~ 0.99. The non-hydrocarbon gases are mainly N2 and CO2 with high N2 and low CO2 contents, ranging from 4% to 8% and 2% to 6%, respectively. The δ13C1 values of natural gas ranged from -63.1 ‰ to -37.7 ‰ and the δ13C2 values ranged from -40.6 ‰ to -24.8 ‰. Natural gas in the plane there is more obvious differences, I zone with high natural gas drying coefficient is high, N2 content is high, CO2 content is low, δ13C1 value is low, mainly due to thermal cracking; Ⅰ with the western drying coefficient is low, N2 The content of δ13C1 is higher in the lower δ13C1 value and higher in the δ13C1 value, while the associated gas and mixed gas source are mainly due to pyrolysis. The composition of natural gas varies a lot. The dry gas generated by the pyrolysis of crude oil with accompanying gas and sapropelic organic matter is dominant, while the natural gas has a large variation of dry coefficient. The main gas associated with crude oil generated by pyrolysis is mainly gas. The regional differences in natural gas properties may be related to the development of fractures and fractures. Natural gas accumulation is dominated by the Himalayan tectonic movement and is dominated by late-stage hydrocarbon accumulation.