Mechanistic investigation of supercritical water gasification of low maturity organic-rich shale using lumped kinetic modeling

The shale in the Chang 7 section of the Ordos Basin has typical continental characteristics of low maturity, and the reaction kinetics behavior of its in-situ gasification is still unclear. In this paper, supercritical water gasification experiments were carried out at temperatures ranging from 500 to 700°C and pressures of 24 MPa. A detailed kinetic network consisting of eight parallel reactions was constructed based on the aggregate parameter method, with a focus on characterizing the evolution law of C₂₊ light hydrocarbons as key intermediate products. The experiment found that the C₂₊ component showed a significant temperature dependence with the reaction time. It continuously accumulated at 500℃, first increased and then decreased at 600℃, and was almost completely consumed at 700℃. The identification of kinetic parameters revealed a significant temperature zoning effect: in the low-temperature zone (500℃), direct decarboxylation of kerogen to CO₂ and C₂₊ steam reforming was dominant; The relative contribution of the direct pyrolysis pathway in the high-temperature zone has significantly increased. Within the heating condition range of 500–700 ℃, the determination coefficient of the established model is between 0.91 and 0.92, and the prediction error is less than 20%, which can reliably describe the evolution of the product distribution over time. The aggregated dynamics model established in this paper provides a new quantitative tool for understanding the conversion mechanism of low-maturity shale in supercritical water environments, and has practical guiding value for the optimization of process parameters in in-situ gasification.