Analysis of Thermal Evolution History of Source Rocks and Natural Gas Accumulation Periods of Upper Paleozoic in the Wuqi Area of the Ordos Basin,China

The distribution of oil and gas resources in the Upper Paleozoic of the Ordos basin is extensive, with well-developed source rocks. However, there is currently a lack of systematic research on source rocks in the Wuqi area, which greatly limits the oil and gas exploration work in this area. This study aims to restore the burial and thermal evolution history of the region, clarify the accumulation periods of source rocks, and promote the fine exploration and development process of oil and gas. It provides a basis for understanding and improving the oil and gas accumulation laws of the Upper Paleozoic in the entire basin. Research suggests that the Wuqi area has undergone four periods of erosion since the Upper Paleozoic, including the end of the Triassic, middle Jurassic, end of the Jurassic, and end of the Cretaceous. The first three periods of erosion were relatively small, mainly distributed between 100-200m, and the end of the Cretaceous period was characterized by significant erosion, which was the main erosion event. The interval transit time method was used to recover the erosion thickness at the end of the Cretaceous period in this study, mainly distributed in the range of 600-1500 m, and the overall erosion amount gradually decreased from east to west. We used vitrinite reflectance to restore palaeogeotherm and PetroMod software combined with parameters such as stratigraphy, lithology, erosion thickness, and boundary condition to reconstruct the burial history and thermal evolution history of the Wuqi area by basin simulation methods. Microscopic observation and combined with fluid inclusion homogenization temperature data were used to further determine the oil and gas accumulation period through a combination of forward and reverse analysis. According to the inclusions and homogenization temperature, it is reflected that there are mainly early and late inclusions in the Upper Paleozoic mudstone in the Wuqi area. Early fluid inclusions are mainly distributed on the secondary enlargement edge of quartz, with temperatures mainly ranging from 110 to 140 ℃; The late stage fluid inclusions are mainly distributed in quartz particle fractures, with temperatures mainly ranging from 100 to 160 ℃, which is the main charging period. The temperature distribution of the two phases of inclusions is continuous process. In conclusion, there were two consecutive oil and gas changes in the Upper Paleozoic in the Wuqi area of the Ordos basin: the first oil and gas charging period was in the Middle Jurassic; The second oil and gas charging period was in the Early Cretaceous.