Pore-scale investigation of halite precipitation and hydrate formation during CO2 injection

Abstract

Carbon dioxide storage in deep saline aquifers and/or depleted hydrocarbon reservoirs is a widely recognized approach for reducing greenhouse gas emissions. However, two key phenomena, halite precipitation and CO2 hydrate formation, pose significant challenges to maintaining injectivity and permeability near the wellbore. This study provides novel experimental insights into how the two pore-scale processes influence porosity loss during CO2 sequestration. A series of controlled microfluidic experiments using glass-based porous networks were conducted to observe the interactions between brine, CO2, and porous media under reservoir-relevant conditions. High-resolution imaging techniques, coupled with advanced image processing algorithms, were employed to analyse water film behaviour and salt crystal growth dynamics. Separate experiments explored the effects of varying pore structures, pressure fluctuations, and thermal conditions on the spatial distribution and morphology of hydrates. The impact of local water saturation variations on fluid displacement and hydrate stability was also examined. The results indicate that heterogeneous pore networks retain more brine than homogeneous ones, leading to more salt precipitation and a maximum observed porosity reduction of 10%. Salt crystallization follows two distinct patterns: smooth-edged crystals form within the brine phase, whereas rough-edged deposits develop at the CO2-brine interface. Hydrate formation exhibits diverse morphologies, amongst others pore-filling, grain-coating, and patchy, hydrate films, influenced by pore size, wettability, and pressure variations. The formed hydrates can reduce porosity by maximum of 15% in the experiments. Additionally, the spatial distribution of hydrates is found to be non-uniform, governed by fluid-phase interactions, with a weak correlation between hydrate and local water saturations.