Inversion and optimization of CO2+O2in situ leaching of blasting-stimulated sandstone-type uranium deposits

Using blasting to induce fracture networks within rock mass is one of the effective reservoir stimulation methods for low-permeability sandstone-type uranium deposits. Nonetheless, there remains a deficiency of suitable theoretical methods to investigate the impact of CO2+O2in situ leaching on blasting-stimulated uranium deposits. In this work, a reaction-flow numerical model based on blasting fractures was first established; second, numerical simulations of blasting-induced fractures in the six injection and two extraction well groups were performed. Finally, the entire process of CO2+O2in situ leaching is simulated under various process parameters to predict the leaching effect of CO2+O2 on blasting-stimulated uranium deposits. Results show that there is a trend of first increasing and then decreasing between the blasting peak pressure and uranium recovery rate, reaching its maximum at a blasting peak pressure of 1000 MPa. The CO2+O2in situ leaching effect of blasting-stimulated uranium deposits is influenced by matrix permeability, O2 concentration, HCO3− concentration, injection rate, and average uranium grade. The matrix permeability, O2 concentration, HCO3− concentration, and average uranium grade are positively correlated with the uranium recovery rate, providing sufficient seepage space and required material composition for CO2+O2in situ leaching. However, the injection rate is negatively correlated with the uranium recovery rate because it reduces the leaching reaction time between the leaching agent and uranium deposits. The important ranking of factors affecting the peak uranium concentration and uranium recovery rate at the CO2+O2in situ leaching period of 900 days is the O2 concentration > matrix permeability > injection rate > average uranium grade > HCO3− concentration. This study serves as a reference for selecting and optimizing technology parameters for blasting and CO2+O2in situ leaching during field tests.