Present-Day Geothermal Characteristics of the Permian–Triassic in the Junggar Basin and Implications for Petroleum Geology

The thermal regime of sedimentary basins is jointly shaped by deep lithospheric dynamics and basin-scale tectonic evolution. Investigating these characteristics not only provides critical insights into unraveling tectono-thermal evolutionary trajectories but also plays a pivotal role in regulating hydrocarbon generation, preservation, and phase differentiation. The Permian–Triassic interval in the central Junggar Basin constitutes a key target for hydrocarbon exploration; however, its geothermal attributes remain poorly constrained owing to limited drilling data and significant burial depths. Leveraging borehole temperature logs, rock thermal property measurements, and integrated well log–seismic datasets, this study refines the present-day geothermal characterization of the Permian–Triassic succession and clarifies its regulatory effects on the hydrocarbon system, thereby laying a solid foundation for future exploration endeavors. Key results are as follows: ① Rock thermal conductivity ranges from 1.009 to 3.915 W/(m·K), which is predominantly controlled by lithology and physical properties (conglomerate > sandstone > mudstone) and exhibits a positive correlation with burial depth. Radiogenic heat production varies between 0.312 and 2.238 μW/m³, depending on the abundance of radioactive elements (mudstone > conglomerate > sandstone), and is lower than that in the adjacent Tarim and Qaidam Basins due to differences in provenance. ② Since the Early Permian, the basin has undergone a gradual attenuation of heat flow. The present-day average geothermal gradient and terrestrial heat flow are 20.8 °C/km and 39.6 mW/m², respectively, showing a spatial pattern of being higher in the east-north and lower in the west-south. With the Permian–Triassic burial depth exceeding 5 km, the measured temperatures (125–200 °C) are notably lower than those of extensional basins in eastern China. ③ Predictive modeling reveals a south-to-north thermal attenuation trend. The Fengcheng and Lower Urho Formations (main source rocks) have average bottom temperatures of 173.1 °C and 191.4 °C, respectively, with most intervals entering the high-over mature gas generation stage. The Triassic Karamay and Baikouquan Formations (reservoirs) exhibit lower basal temperatures (145.6 °C and 150.6 °C), remaining within the liquid oil window. The Permian Upper Urho Formation (average basal temperature of 163.2 °C) has experienced extensive oil cracking in the southern part of the basin, which is unfavorable for liquid oil preservation.