Study of the residual carbon oxidation trigger mechanism in fractured oil shale formation under real condition

Abstract

The autothermic pyrolysis in-situ conversion process (ATS) has a considerable advantage in reducing the development costs of oil shale. However, the trigger mechanism of autothermic pyrolysis oxidation reaction in different fractured oil shale formations is not precise. This study conducts a one-dimensional residual carbon oxidation experiment on the oil shale sample, taking into account the overburden pressure. The trigger condition and parameters are determined through the energy analysis during residual carbon oxidation in the fractured oil shale. A trigger simulation model of autothermic pyrolysis oxidation reaction in different fractured oil shale formations is proposed and verified by the temperature field evolution. The results indicate that the heterogeneous oxidation reaction produces a high permeability channel in the oil shale formation, which can further improve the flow conductivity of the oil shale formation. The trigger threshold of the residual carbon oxidation reaction in the fractured oil shale formation was closely associated with the carbon residue concentration (> 2.59 × 10⁴ mol/m³), oxygen content (>15 %), and gas crossflow between the fracture and matrix (0.56–0.78). This study has important theoretical guiding significance for triggering and controlling the ATS.