Hydrocarbon generation kinetics of Paleogene coal in Xihu sag, East China Sea Basin

Through thermal simulation experiments and simulation analysis of hydrocarbon generation kinetics under the closed system with high temperature and high pressure, this paper obtains the yields and kinetic parameters of gaseous hydrocarbons generated by coal from the Paleogene Pinghu Formation and Huagang Formation in Xihu sag. Further in combination with the evolution history of paleo-temperature and thermal evolution, the paper restores the hydrocarbon generation and evolution history of coal from the Paleogene Pinghu Formation and Huagang Formation in the western slope belt, the western sub-sag and the central structural belt of Xihu sag, and establishes the gas generation and evolution model of coal in the study area based on the predicted vitrinite reflectance value (Ro). The research results show that gas produced by coal in Xihu sag is domininated by methane (C1), with less heavy hydrocarbon gas (C2-C5). The rate of rise in the yield of C1 and the total yield of gaseous hydrocarbons (C1-C5) is the largest in the high mature stage of coal (1.10%≤Ro<2.20%), followed by the mature stage (0.50%≤Ro<1.10%), and the smallest in the over-mature stage (Ro≥2.20%). Moreover, the heavy hydrocarbon gas with different numbers of carbon atom (C2, C3, C4 and C5) have different main cracking periods. During the hydrocarbon generation and evolution of coal in Xihu sag, coal in Pinghu Formation and Huagang Formation in the western slope belt produced the least gaseous hydrocarbons and had the worst hydrocarbon generation conditions; while Pinghu Formation and Huagang Formation in the western sub-sag and central structural belt produces more gaseous hydrocarbons and are favorable source areas. The yield of gaseous hydrocarbon from coal in Huagang Formation is much lower than that in Pinghu Formation, and it has not yet reached the hydrocarbon generation peak. © 2020, Editorial Office of ACTA PETROLEI SINICA. All right reserved.