Pore-scale thermo-hydro-chemical coupling numerical simulation for in-situ thermal upgrading of low-to-medium maturity shale oil

In-situ thermal upgrading (ITU) is key to the efficient exploitation of low-to-medium maturity shale oil (LMSO) resources. It is a complex process involving chemical reaction, heat transfer, and fluid flow. To thoroughly investigate the pyrolysis kinetics of LMSO at the pore-scale, this study proposes a coupled thermo-hydro-chemical numerical simulation approach. A novel multi-component characteristic parameter model is developed to quantify the dynamic evolution of fluid properties during multi-stage kerogen pyrolysis. Comparative analysis reveals that the original static parameter model underestimates the production of methane, other gases, and light oil, while overestimating that of heavy oil. The pyrolysis process induces a remarkable transformation in the reservoir properties, with the porosity and permeability increasing from 0.013 and 0.0006 mD to 0.28 and 6.4 mD, respectively, which significantly enhances the flow capacity. Sensitivity analysis reveals that the kerogen content is positively correlated with the total yield of cracking products. When kerogen content increases by 28.6 %, the total yields of heavy oil, light oil, other gases, and methane increase by 50.4 %, 20.8 %, 17.8 %, and 27.3 %, respectively. Furthermore, when specific heat capacity rises from 1380 to 1980 J/(kg·K), the kerogen pyrolysis time increases by a factor of 1.4. Conversely, increasing heating rate by a factor of 1.9 reduces the cracking time by 13.6 min. The maximum yields of heavy oil, light oil, and other gases occurred at distinct thermal thresholds of 400, 500, and 570 °C, respectively. This study provides a theoretical basis for optimizing ITU process parameters and improving the energy efficiency of LMSO.