Kinetics and model of gas generation of source rocks in the deepwater area, Qiongdongnan Basin

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 (E a) distribution of C1–C5 generation ranges from 50 to 74 kcal/mol with a frequency factor of 2.4×1015 s−1 for the neritic mudstone and the E a distribution of C1–C5 generation ranges from 49 to 73 kcal/mol with a frequency factor of 8.92×1013 s−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 R o (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.