Coupling MRI and XRCT to Resolve Structure–Transport Evolution During Enzyme‐Induced Calcite Precipitation at the REV Scale

The aim of this study is to understand how enzyme‐induced calcite precipitation (EICP) modifies flow and transport in porous media, as this is essential for developing sustainable approaches to soil stabilization, permeability control, and groundwater management. For this, we investigated the coupled evolution of pore structure and hydraulic properties during EICP at the representative elementary volume (REV) scale using a dual non‐invasive imaging approach combining X‐ray computed tomography (XRCT) and magnetic resonance imaging (MRI). Three replicate sand columns with initial permeabilities between 22 × 10 −12 m 2 and 25 × 10 −12 m 2 were treated with EICP using a constant flow injection and solutions of 0.5 M CaCl 2 , 0.5 M urea, and 5.0 g L −1 jack bean meal. Over six injection cycles (175 pore volumes), permeability decreased by more than three orders of magnitude, while average porosity declined moderately from 0.38 to 0.28. XRCT revealed that precipitation was concentrated near the inlet, where the surface to volume ratio increased from 0.055 to 0.065 μm −1 and tortuosity rose from ∼2.0 to ∼3.5. MRI measurements showed corresponding localized reductions in water content and relaxation times, with T 1 decreasing from ∼1.5 to ∼1.0 s and T 2 from ∼50 to ∼30 ms. The combined imaging results indicate a two‐stage precipitation process with early pore‐throat blockage followed by progressive narrowing of pore bodies. These findings demonstrate that permeability loss is governed not only by porosity reduction but also by precipitation distribution.