Gas–liquid–solid coordinated transport behavior and pore clogging mechanisms during CO2 <b>+</b> O2 <i>in situ</i> leaching of sandstone-type uranium deposits

The CO2 + O2in situ leaching (ISL) of sandstone-type uranium deposits faces the significant challenge of reservoir clogging, which has become a critical bottleneck limiting uranium resource extraction. This study employs a coupled volume of fluid-computational fluid dynamics-discrete element method to investigate the synergistic migration processes of gas, liquid, and solid phases under the influence of multiple factors, aiming to elucidate the mechanisms and governing principles of pore clogging in uranium reservoirs. Results show that the spatial distribution of pore throats and particle interactions alter fluid migration patterns, increasing the uncertainty of fluid flow and leading to solid clogging. CO2 + O2 moves with the leaching solution, forming a turbulent gas–liquid interface; some bubbles become trapped in pore throats due to surface tension, causing gas clogging. Increases in particle injection rate, particle size, particle irregularity, and reservoir heterogeneity all exacerbate pore clogging. Conversely, a higher fluid injection rate can reduce particle sedimentation and reactivate retained particles, promoting pore unclogging. The proportion of residual particles follows a logistic function trend with increasing particle and fluid injection rates and an exponential trend with particle diameter. Particle irregularity and reservoir heterogeneity increase the proportion of residual particles by factors of 2.13 and 1.12, respectively. For clogged uranium deposits, it is recommended to first apply chemical methods to reduce soluble mineral particles, then increase the leaching solution injection rate to mobilize retained particles, and finally employ low-amplitude, high-frequency reservoir stimulation for further unclogging. These strategies can extend the ISL mining lifespan and improve uranium recovery.