Understanding Porosity-Permeability Coupling in Natural and Fabricated Reactive Porous Media

Abstract

Predicting how geochemical reactions alter pore structure and how those structural changes drive macroscopic porosity–permeability evolution remains a major unsolved challenge. Geochemical reactions modify pore shape, size, and connectivity. Yet, permeability responses depend on the spatial location of reactions within the pore network rather than on bulk porosity alone. Classical porosity–permeability relationships cannot fully capture these changes, and pore-scale heterogeneity in natural formations further limits the predictive accuracy. Hence, this dissertation presents four studies advancing understanding of geochemical reactions and their impact on porosity–permeability evolution in fabricated and natural porous media, employing 3D X-ray micro-CT imaging, pore network modeling, and core-flooding experiments to elucidate pore-scale controls on hydraulic evolution. The first study demonstrated that surface-functionalized 3D-printed cores provide a geochemical experimental platform. Functionalized samples accumulated ~2.6 vol% calcite uniformly throughout the pore network compared to less than 1.1 vol% near the inlet in unfunctionalized samples, establishing that surface energy governs both the magnitude and spatial pattern of mineral precipitation. The second study revealed that permeability is governed by pore-throat occlusion rather than by changes in bulk porosity since functionalized cores with 9–10% porosity loss experienced permeability reductions exceeding 135%, while unfunctionalized cores with only 5% porosity loss exhibited a 88% reduction. The third study characterized pore-scale heterogeneity in eleven Lower Tuscaloosa Formation core samples, finding a nearly six-fold variation in simulated permeability (4.2–22.9 mD) despite similar bulk porosities (20–24%), with empirical models explaining at most half the permeability variance (R² ≤ 0.52), suggesting that pore connectivity should be considered, rather than bulk porosity, to predict hydraulic behavior. The fourth study showed that resin-based 3D printing reproducibly replicates the natural rock pore structure, with replicate samples exhibiting only approximately 2% structural differences and 0.3% differences in porosity. A core-flooding experiment revealed calcite preferentially localized at grain boundaries and small pore throats with a pronounced inlet-to-outlet gradient. Together, these findings demonstrate that pore-throat geometry and surface chemistry are the primary controls on precipitation-driven permeability loss, and that pore network topology governs hydraulic behavior in both fabricated and natural porous media, supporting development of next-generation porosity–permeability upscaling frameworks.