Hydrodynamic and leaching efficiency comparison of horizontal and vertical well Systems in Uranium in-Situ Leaching

Vertical wells are predominantly used for both injection and extraction in uranium in-Situ leaching (ISL), yet they often produce uneven spreading of leaching solution and relatively low leaching efficiency. Horizontal wells, widely applied in oil and shale-gas operations, offer a plausible alternative for solution injection, but their suitability for uranium ISL remains underexplored. In this paper, we compared hydrodynamic performance and leaching extent between horizontal injection/vertical pumping (HIVE) systems and traditional vertical injection-pumping (TVIE) systems through numerical modelling. For HIVE flow simulations, MODFLOW-CFP, initially designed for karst aquifers, was utilized, while MODFLOW was employed for TVIE systems. Based on these simulations, particle tracking simulations were used to trace the flow paths of the leaching solution, and the Alpha-shape algorithm automatically extracted the leaching extent from the particle trajectories that reached the pumping wells. Simulation results highlight HIVEs can effectively reduce low-velocity zones and mitigate leaching stagnant zones commonly found between injection wells in TVIE systems. Although the total leaching volume in HIVEs was generally lower than that in TVIEs, the leaching volume within the uranium orebody was comparable to or even slightly greater than TVIEs. Consequently, a large fraction of the leaching solution remains within the orebody, leading to higher leaching efficiency for HIVEs compared to TIVEs. Overall, these findings suggest that HIVEs could be a promising alternative to traditional vertical well systems in in-situ uranium leaching across different hydrogeological conditions except in relatively thin orebodies, where TVIE may still achieve slightly higher leaching efficiency. Future studies should examine HIVEs in heterogeneous aquifers and employ reactive multicomponent models to better quantify its performance relative to TVIEs.