柴达木盆地北缘天然气地球化学特征及其石油地质意义

摘要

In order to understand the generation and distribution of natural gas in the northern margin of the Qaidam Basin,the geochemical characteristics of natural gas are analysed with both natural gas composition and carbon isotope.The results show that the natural gas is dominated by methane,but the content of heavy hydrocarbons is relatively high.There are obvious differences in natural gas composition in different structural belts.Research on carbon isotopes indicated that the δ13C1 and δ13C2 values are-36.4‰~-19.3‰ and-27.4‰~-19.82‰,respectively.The identification of na-tural gas shows that the main type of natural gas in this area is coal-generated gas and is derived from Jurassic source rocks.Carbon isotopic distribution of the northern margin of the Qaidam Basin is characterized by positive sequence,and there are carbon isotope reversal phenomena in some areas due to different maturity,different mixture types of sources and the gas generation from source rocks in the high-mature stage.The distribution of oil and gas reserves in the northern margin of the Qaidam Basin is characterized by spatial zonation from the outer edges to the centre of the basin and is controlled by the source rock maturity.The natural gas is located in mature and high maturity areas.Future promising areas for exploration have been put forward,which include Lenghu NO.6 and NO.7,Eboliang-Hulushan tectonic belt and the foreland of the Altun Mountains.%为了明确柴达木盆地北缘地区天然气的成因和天然气分布规律,综合利用天然气组份及碳同位素等手段对天然气地球化学特征进行了分析.研究表明,柴北缘天然气以甲烷为主,重烃含量相对较高,不同构造带天然气组分具有明显的差异性.碳同位素分析表明,δ13C1和δ13C2值分别介于-36.4‰~19.3‰和-27.4‰~-19.82‰.天然气成因鉴别表明,该区天然气主体为煤型气,来自侏罗系烃源岩.柴北缘碳同位素分布主体为正序列特征,受不同成熟度、不同类型源岩混合以及过成熟阶段源岩等因素影响,部分地区存在天然气碳同位素倒转现象.柴北缘天然气平面分布具有分带性,烃源岩成熟度控制了油气分布,天然气位于成熟-高成熟区及附近.冷湖六号-冷湖七号、鄂博梁-葫芦山构造带以及阿尔金山前是下一步天然气勘探的重点领域.