The Shahezi Formation is the main source rock formation in the deep part of the Xujiaweizi Fault Depression. In this study, firstly, based on measured pressure data and logging data, analyzed with methods such as fluid inclusion testing and basin numerical simulation, the pressure evolution history of the Shahezi Formation was systematically reconstructed. Secondly, hydrocarbon generation simulation experiments were carried out under pressures of 45, 70, and 100 MPa to reveal the influence of pressure on the hydrocarbon generation and expulsion process of organic matter. The results showed that the evolution of the pore pressure could be divided into four stages. Prior to the end of the early Cretaceous (~104 Ma), the Xujiaweizi Fault Depression was in a normal-pressure state. In the early Late Cretaceous (104–78 Ma), overpressure was generated in the source rocks due to undercompaction and hydrocarbon generation, which was a stage of rapid pressure increase. In the Late Cretaceous (78–65 Ma), a large amount of gas was generated in the source rocks, and the pressure reached the highest value. From the early Paleogene to the present (65–0 Ma), it has been a stage of slow pressure decrease. The strata have experienced slow uplift, and the pressure has gradually decreased. The effect of high pressure can promote the conversion of heavy hydrocarbon gases in the C1–C5 components to methane, but the promoting effect is limited. In contrast, high pressure has a certain effect on the preservation of liquid hydrocarbon components, and this preservation effect may be caused by the conversion of unstable saturated hydrocarbons to aromatic hydrocarbons.

The Hexiwu structural belt is an important oil and gas exploration area in Langgu Sag, Bohai Bay Basin, China. The source of oil and gas has always been the focus of exploration. In this study, the crude oil samples from the rich oil layers in the north, middle and south of the Hexiwu structural belt were used to carry out the analyses of crude oil molecular geochemical characteristics and oil source correlation in the whole area. Combined with source rock evaluation and oil source analysis, the geochemical parameter characteristic chart was used to clarify the existence of two sets of source rocks in the Hexiwu structural belt. The hydrocarbon supply situation and specific classification of crude oil types in Hexiwu structural belt was determined. The crude oil in the Hexiwu tectonic belt can be divided into three types. Type I crude oil is the source rock of the lower Es₃ section of Hancun Trough, which is mainly distributed in the north-central Hexiwu tectonic belt. Type II oils occur in the southern Hexiwu structural belt and are primarily sourced from mixed hydrocarbons generated by the Lower Es₃ and Upper Es₄ source rocks in the Hancun–Caojiawu area. The type III crude oil is the source rock of the upper Es₄ section of Caojiawu–Hancun, which is mainly distributed in the south of the Hexiwu tectonic belt. The classification of reservoir types and the definition of source in the Hexiwu structural belt provide theoretical guidance for future oil exploration in the Hexiwu structural belt, thus providing a new framework of oil and gas exploration in the Hexiwu structural belt.