The Impact of Differential Thermal Evolution on Coalbed Methane Accumulation of Upper Palaeozoic Strata in the Eastern Ordos Basin

The eastern Ordos Basin is rich in coalbed methane resources, with distinct accumulation and generation characteristics observed across different structural zones. Therefore, this study focuses on the eastern margin, utilizing vitrinite reflectance, geochemical parameters, and fluid inclusion thermometry data to reconstruct the thermal evolution history and simulate hydrocarbon generation. By comparing the differential evolution of Upper Palaeozoic coal seams in the eastern margin, it was found that the northern area was at a low-maturity stage in the Late Triassic, with limited hydrocarbon generation. The Early Cretaceous was the primary hydrocarbon generation period, with accumulation time occurring between 145 and 130 Ma. The peak hydrocarbon generation occurred at 140 Ma, but with relatively weak intensity, producing less than 0.01 Mtons. In contrast, the southern area's main reservoir formation period was between 135 and 120 Ma, reaching a peak hydrocarbon generation of 0.02 Mtons at 120 Ma. Overall, the hydrocarbon accumulation in the eastern margin of the basin occurred between 145 and 120 Ma. The geochemical characteristics of the coal-bearing source rocks show little variation, and the thermal evolution and hydrocarbon generation processes are similar. The quality of the source rock primarily affects hydrocarbon generation intensity, while the formation of coalbed gas is mainly constrained by structural thermal evolution. This study contributes to a deeper understanding of the thermal evolution and hydrocarbon generation processes of deep Upper Palaeozoic coal seams in the eastern margin of the Ordos Basin. It provides valuable insights for coalbed gas accumulation and prediction.