Evolution of pore structure, fracture morphology and permeability during CO2+O2 in-situ leaching process of fractured sandstone

This work is organized to reveal the influence mechanism and law of CO2+O2 in situ leaching on pore permeability characteristics of stimulated deposits. Results show that geochemical reactions during the CO2+O2 ISL process are complex, the dolomite and potassium feldspar are dissolved, while the clay mineral precipitates are formed. The response characteristics and mechanisms of pore-fracture structures differ between the single and multi-fractured samples during the CO2+O2 ISL process. The pore number density of the single-fractured sample increases while porosity decreases, causing larger pores to evolve into smaller ones. While the porosity and fracture volume of the multi-fractured sample increase significantly. The permeability characteristics of fractured samples are consistent with the evolution of pore-fracture structures. The multi-fractured sample possesses a higher fracture compression coefficient and lower PLR due to the larger compressive space, the self-supporting effect of fracture network and the scouring effect of leaching solution. Although creating a single fracture in reservoir stimulation can enhance the original deposit permeability, the conductivity will gradually decline during the subsequent CO2+O2 ISL process. Optimizing reservoir stimulation techniques to create complex fracture networks within deposits can enhance overall permeability and weaken the permeability reduction effect, ensuring the efficient extraction of uranium resources.