Kinetics and model of gas generation of source rocks in the deepwater area, Qiongdongnan Basin
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摘要: 为研究琼东南盆地深水区烃源岩的生烃过程和生气潜力,应用封闭体系高温高压热模拟实验和Kinetics软件,获取了盆内渐新统崖城组主力烃源岩(煤和浅海泥岩)生气的活化能和频率因子等动力学参数:浅海泥岩的C1-C5活化能分布介于50-74 kcal/mol之间、频率因子是2.4×1015s-1,煤样的C1-C5活化能分布介于49-73 kcal/mol之间、频率因子是8.92×1013s-1;进而结合地层埋藏史和热史资料,建立了崖城组烃源岩逼近地下条件的生气模式,揭示其主生气阶段对应的Ro在1.25%-2.85%之间;同时,模拟再现了深水区陵水凹陷中部、南部斜坡和凸起等不同构造位置的崖城组烃源岩生气史.其中,陵水凹陷中部和南斜坡崖城组烃源岩大量生气时间分别发生在距今10Ma和5Ma;后者的生气高峰期出现在距今3 Ma之后,晚期快速生气且生气强度大(20×108-60×108 m3/km2),为该区天然气聚集成藏提供了有利的烃源条件.本研究成果对盆内深水勘探区带选择和目标评价有重要指导作用.Abstract: In order to investigate the hydrocarbon generation process and gas potentials of source rocks in deepwater area of the Qiongdongnan Basin, kinetic parameters of gas generation (activation energy distribution and frequency factor) of the Yacheng Formation source rocks (coal and neritic mudstones) was determined by thermal simulation experiments in the closed system and the specific KINETICS Software. The results show that the activation energy (Ea) distribution of C1-C5 generation ranges from 50 to 74 kcal/mol with a frequency factor of 2.4×1015s-1 for the neritic mudstone and the Ea distribution of C1-C5 generation ranges from 49 to 73 kcal/mol with a frequency factor of 8.92×1013s-1 for the coal. On the basis of these kinetic parameters and combined with the data of sedimentary burial and paleothermal histories, the gas generation model of the Yacheng Formation source rocks closer to geological condition was worked out, indicating its main gas generation stage at Ro (vitrinite reflectance) of 1.25%-2.8%. Meanwhile, the gas generation process of the source rocks of different structural locations (central part, southern slope and south low uplift) in the Lingshui Sag was simulated. Among them, the gas generation of the Yacheng Formation source rocks in the central part and the southern slope of the sag entered the main gas window at 10 and 5 Ma respectively and the peak gas generation in the southern slope occurred at 3 Ma. The very late peak gas generation and the relatively large gas potential indices (GPI: 20×108-60×108 m3/km2) would provide favorable conditions for the accumulation of large natural gas reserves in the deepwater area.
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