Thermal evolution and hydrocarbon generation history of the Weibei uplift in the Ordos Basin

Abstract

The Weibei uplift in the Ordos Basin has a distinctive tectonic setting and intricate evolutionary history. Along these lines, we have used the stratum temperature, apatite fission track, and vitrinite reflectance data to restore the thermal and hydrocarbon generation histories of the Weibei uplift. The average value of the present geothermal gradient of the Weibei uplift was 27.9°C/km, and the heat flow was 64.9 mW/m2. The Weibei uplift exhibited a moderate geothermal field. Three uplift cooling events occurred in the Weibei uplift during the Mesozoic era: the late Jurassic-early Cretaceous (162–125 Ma), the late Cretaceous (105–65 Ma), and the Eocene-Oligocene (40–27 Ma). The uplift history indicates an early uplift in the south region and a late uplift in the later stage. The thermal evolution history simulation demonstrates that the lower Palaeozoic Ordovician source rocks began to enter the hydrocarbon generation threshold in the middle Permian-late Permian (270 Ma) era and joined the hydrocarbon generation peak in the early-middle Jurassic event (180 Ma). The upper Palaeozoic Carboniferous-Permian source rocks began to enter the hydrocarbon generation threshold in the later period of the middle Permian period (235 Ma). They joined the hydrocarbon generation peak in the late Jurassic-early Cretaceous period (150 Ma). In addition, Triassic source rocks entered the hydrocarbon generation threshold in the early Cretaceous era (135 Ma) and did not enter the hydrocarbon generation peak until now. The low geothermal gradient of the Weibei uplift in the Palaeozoic-early Mesozoic reached the maximum paleotemperature in the early Mesozoic era (100 Ma) because of tectonic thermal events. The highest geothermal gradient of the early Cretaceous reached 51.5°C/km. The peak period of the hydrocarbon generation of source rocks of the different horizons in the Weibei uplift was regulated by the geothermal field of the early Cretaceous event. Since the late Cretaceous period, the stratum has been uplifted and cooled rapidly, and the hydrocarbon generation process of the source rocks has ceased.