Present-day temperature and pressure fields in key areas of Northeast China: Implications for unconventional resource evaluation

The temperature-pressure fields within hydrocarbon-bearing basins are key geological factors controlling hydrocarbon generation, migration, and accumulation. In this study, we focus on the Qingshankou Formation in the northern part of the central depression of the Songliao Basin, China. A multi-parameter weighted evaluation model was created using present temperature-pressure field characteristics, with formation temperature-pressure as core variables, to evaluate shale oil resource potential. In addition, we explored the control mechanisms of temperature-pressure evolution during geological history on shale oil accumulation and further assessed the applicability of the proposed method. Our results show that the geothermal gradient of the Qingshankou Formation decreases from Member 1 to Member 3 (3.84 °C/100 m, 2.93 °C/100 m, and 2.49 °C/100 m, respectively). High-temperature zones are widely distributed in the Gulong sag, with the average temperature of the Gulong shale exceeding 95 °C and reaching an average of approximately 115 °C. Overpressure in the Qingshankou Formation exhibits a west-high to east-low trend. The overpressure zones of the Gulong shale are mainly concentrated in the Qijia-Gulong and Sanzhao sag, with average pressure coefficients of 1.52 and 1.36, respectively. The Opc model identified Class I and II favorable zones, mainly located in the central and southern parts of the Gulong Sag, as well as the central and southwestern Sanzhao Sag, with estimated shale oil resources of $7.1\times {10}^8$ tons and $17.2\times {10}^8$ tons, respectively. Evolutionary profiles from representative wells indicate that elevated temperatures enhance organic matter maturation and light oil generation, improving shale oil mobility, while overpressure suppresses hydrocarbon dissipation and provides a sufficient driving force for oil production. This study demonstrates that present-day temperature-pressure fields effectively reflect the evolution trends of paleo-thermal and pressure regimes. The proposed evaluation method shows strong applicability and scalability, offering a new technical framework and theoretical foundation for the exploration of unconventional hydrocarbon resources.