The Coupling Relationship between Paleofluid Pressure Evolution and Hydrocarbon-Charging Events in the Deep of Biyang Depression, Central China

The deep area of Biyang depression contains considerable lithologic hydrocarbon reservoirs, and the present pressure is mostly shown as normal-weak overpressure system. In this study, the paleopressure evolution history of the deep depression has been revealed combining with the numerical simulation and thermodynamics of fluid inclusion. The hydrocarbon generation history shows that the Biyang depression reached the peak of hydrocarbon generation when it reached the maximum burial depth at the end of the sedimentation of the Liaozhuang Formation (about 23.03 Ma). After the formation uplift, the hydrocarbon generation weakened and approached to a stop. Two different oil inclusions were detected in the deep sandstone reservoir, which were the orange-yellow fluorescent oil inclusion with low maturity and the blue-green fluorescent oil inclusion with relatively high maturity. The homogenization temperature of the inclusion combined with the burial history chart shows that the hydrocarbon charging time is 35.4-30.3 Ma and 27.8-26.5 Ma respectively. The numerical simulation results show that the pressure in the deep continued to increase from 39.3 Ma, and reached an obviously overpressure at about 23.03 Ma at the deepest burial. The pressure coefficient reached to about 1.5, and then the overpressure weakened and evolved into the present normal-weak overpressure system. The paleo-pressure of the thermodynamic simulation of the inclusions also shows a similar evolutionary trend. In conclusion, the coupling of the hydrocarbon generation period, the charging event and the overpressure period indicate that the present lithologic reservoir in deep is attributed to two-stage hydrocarbon charging driven by overpressure caused by hydrocarbon generation.