Abstract:It is of great significance for deep oil and gas exploration to understand the origin and evolution behind overpressure. Overpressure occurs in the deep Shahezi Formation of Xujiaweizi fault depression. However, due to limited degree of exploration, there are some problems in the study area, such as unclear understanding of the origin of overpressure and the vague investigation of overpressure evolution. To clarify the impact of overpressure on oil and gas migration and accumulation in the study area, this study focuses on the research of the origin and evolution of overpressure in the Shahezi Formation of the study area, utilizing single well logging parameters and combining methods such as microthermometry of fluid inclusions, laser Raman spectrum, and basin simulation. The results show that the overpressure of the Shahezi Formation in Xujiaweizi fault depression is primarily generated by hydrocarbon generation pressurization, and the evolution of overpressure is closely related to hydrocarbon generation. The development of overpressure can be divided into two evolutionary stages: early hydrocarbon generation pressurization and late uplift release, with slight variations in different regions. Tight glutenite gas reservoirs in the Shahezi Formation are characterized by continuous charging. The overall charging period ranges from the late Denglouku to the early Mingshui (110–67 Ma ago). There is an obvious paleo-overpressure during the gas reservoir formation period. The gas generation period of source rocks occurred approximately 125–60 Ma ago, and the main gas generation period (112–67 Ma ago) highly coincides with the period of natural gas charging. The anomalously high pressure during the accumulation period is considered the significant driving force for natural gas charging. In addition, the sustained effect of overpressure provides better conditions for the preservation of tight gas reservoirs within the source. The results of the study are of guiding significance for the in-depth exploration and development of deep tight sandstone gas in the Shahezi Formation of Xujiaweizi fault depression.
