Self-Enhancing Halite Growth Creates Secondary Porous Networks During CO2 Storage in Saline Aquifers

Abstract

Salt precipitation during CO2 injection into saline aquifers obstructs flow-controlling pore throats and reduces permeability, yet reactive transport models assume salt forms dispersed, non-porous crystals with minimal flow impact. We demonstrate that halite instead creates three-dimensional porous networks with 40% internal porosity through self-enhancing growth mechanisms absent from current models. Time-lapse X-ray micro-computed tomography and spectral imaging reveal preferential nucleation at gas-liquid interfaces, where porous hydrophilic aggregates generate capillary suction that draws brine films toward precipitation sites, accelerating growth and expanding reactive surface area in a positive feedback loop. Spectral tomography shows systematic density gradients reflecting two-stage precipitation: dense macrocrystalline cores formed under moderate supersaturation and evaporation, surrounded by microcrystalline overgrowths from rapid late-stage dynamics. These overgrowths create umbrella-like crusts that encapsulate residual brine beneath surface layers. This porous architecture explains why modest porosity reduction causes severe permeability decline, as aggregates preferentially obstruct flow percolation pathways rather than uniformly cementing grains or filling pore space. Five interconnected mechanisms drive self-enhancing growth across nano- to centimeter scales: interface nucleation, secondary porous structure formation, steep concentration gradients, hydrophilic substrate film maintenance, and capillary-driven solute delivery. Our quantitative characterization of internal salt architecture, reactive surface areas, and pore connectivity provides essential parameters for improving predictive models of evaporation-precipitation dynamics in carbon storage, soil salinization, and cultural heritage preservation.