## 5 Discussion
### Hydrocarbon Charging Time and Period  
Fluid inclusions contain rich information on reservoirs and minerals and provide the best records of the history of hydrocarbon migration and accumulation, thereby facilitating  
Figure 8: Comparison of oil and gas sources in the HZ-A structure “double-Paleo” field. (**A**) Comparison of oil and sources. (**B**) Comparison of gas and sources. hydrocarbon accumulation chronology research [14; 15; 16]. The uniform temperature of the brine inclusions that coexist with hydrocarbon inclusions in the reservoir can represent the stratum temperature at the time when the oil and gas entered the reservoir [17]. With reference to the burial history and thermal history, the time when oil and gas entered the reservoir can be indirectly determined. The charging period of oil and gas can then be derived. The oil and gas charging of the HZ-A structure pre-Paleogene buried hill lasted a relatively long time. The hydrocarbon inclusions were captured from 20 Ma to the present. Hence, the time span of oil and gas charging was long. However, since the time corresponding to the main peak of the uniform temperature of the brine inclusions was concentrated from 13.8 Ma--5.3 Ma, the oil- and gas charging scale was greatest in this period, and this period represents the main oil and gas charging period of the pre-Paleogene buried hills (Figure 9A). The oil and gas charging time of the HZ-A structure Paleogene Wenchang Formation was later than that of the pre-Paleogene buried hills. The hydrocarbon inclusions were captured from 12 Ma to the present. Its brine inclusion uniform temperature distribution featured a narrow double-peak distribution, revealing that the main oil and gas charging events occurred in two periods, with the first occurring at 12-10 Ma and the second occurring at 5.3-3 Ma (Figure 9B). The oil and gas charging time of the Paleogene Enping Formation in the HZ-A structure was close to that of the Paleogene Wenchang Formation. The hydrocarbon inclusions were captured from 14 Ma to the present. In addition, unlike the Paleogene Wenchang Formation, the Paleogene Enping Formation of the Paleogene had a relatively concentrated hydrocarbon inclusion capture time, with the main capture period extending from 7 Ma to the present, corresponding to a large-scale hydrocarbon charging event (Figure 9C). Figure 9: _Cont._  
Figure 9: Oil and gas charging time in the HZ-A structure “double-Paleo” field. **(A)** Oil and gas charging time in the pre-Paleogene buried hills. **(B)** Oil and gas charging time in the Paleogene WC formation. **(C)** Oil and gas charging time in the Paleogene EP formation. In summary, the main oil and gas charging periods for the HZ-A structure strata were all after 13.8 Ma. Among them, the main charging period of the pre-Paleogene buried hills was the earliest (13.8-5.3 Ma), that of the Paleogene Enping Formation was the latest (7-0 Ma), and that of the Paleogene Wenchang Formation was between the two (12-10 Ma and 5.3-3 Ma). It is known from comparing the hydrocarbon fluid maturity levels of the brine inclusions of the HZ-A structure strata that the hydrocarbon fluid maturity distribution characteristics of the HZ-A structure double Paleogene field were similar to the distribution characteristics of the main charging period of brine inclusions. Among the hydrocarbon fluids, natural gas charging occurred the latest, and asphalt (low-maturity oil deasphalted product) had a low maturity and an early charging period. Normal crude oil had a wide range of maturity distributions, indicating that crude oil had multiple charging periods. That is, the HZ-A structure double Paleogene field experienced low-maturity crude oil charging during the strata's early accumulation stages.