Rapid-heating open-system thermal simulation of oil shale residue and hydrocarbon product evolution characteristics

In recent years, in-situ conversion has shown great potential for large-scale oil shale exploitation, but the evolution of hydrocarbon products and residues during thermal conversion remains insufficiently studied. Using oil shale samples from the Fushun, Huadian, and Meihe basins, we conducted heating experiments in a rapid open system to investigate hydrocarbon generation and residue evolution at different stages, providing theoretical support for in-situ recovery. At ≤ 300 °C, water accounts for 40.0–57.4 wt.%, oil yield is below 1 wt.%, and hydrocarbon potential remains excellent. At 400–475 °C, organic matter is greatly consumed, with TOC reduced by 7.7–9.8 wt.%, and S2 conversion reaches 96.19–97.18%. Hydrocarbon potential drops from excellent to good, marking the main oil generation and expulsion stage. At 520 °C, oil and water yields stabilize, gas yield rises slightly with dry gas as the main component, and residual potential gradually declines. Fushun oil shale is dominated by type I kerogen, whereas Huadian and Meihe oil shales are dominated by type II, with decreasing oil-generating capacity. Organic matter enters the oil window at 300 °C and peaks at 475 °C. We recommend 400–475 °C as the optimal heating range for oil shale in-situ conversion.