Speaker
Description
To achieve the goal of limiting the global temperature increase to below 2°C and avoid the adverse effects of climate change, the removal of CO2 from the atmosphere requires the simultaneous application of carbon capture, utilization, and storage (CCUS) methods. Among these, carbon mineralization is a promising approach that can securely trap a substantial amount of CO2. Ultramafic rocks, such as peridotites, are rich in minerals like olivine and pyroxene, which can react with CO2 to form solid calcite and magnesite through dual dissolution-precipitation processes. However, these ultramafic rocks are notoriously low in permeability, and mechanical cracks have been proposed to increase the reactive surface area [1]. A previous study [2] suggested that dissolution and precipitation were spatially decoupled in the presence of advective or convective flow through the cracked solid. Multiple etch pits resulting from the dissolution process were observed on the surfaces of the reacted olivine grains and could facilitate further cracking. However, the formation mechanisms of these etch pits, including their size, shape, and density under realistic conditions such as shear cracks subjected to high confining pressures and fluid with variable CO2 contents and flow rates, remain unclear. To address these uncertainties, we conducted a core-flooding experiment using both aqueous and wet super critical CO2. The aqueous CO2 was premixed at various temperatures and pressures to generate different CO2 solubility levels. Using a triaxial direct-shear (TDS) system, we induced shear fractures in the peridotite core under subsurface temperature and pressure conditions. These fractures exhibit small-scale geometrical characteristics, such as tortuosity, roughness, aperture distribution, and asperity contacts, that are representative of subsurface cracks and critical for etch pit formation, crack evolution, and reaction transport. Following the creation of the shear cracks, we evaluated the absolute permeability of the fractured core under different effective confining pressures. Effluent samples were collected for each permeability measurement and analyzed using inductively coupled plasma–optical emission spectroscopy (ICP-OES) to monitor elemental changes, providing insights into mineral dissolution. High-resolution X-ray computed tomography (~45 μm) was used to visualize etch pit formation and the subsequent evolution of crack networks. Post-experiment analysis of the fractured surfaces using scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS) unveiled changes in chemical composition within and around the etch pits. The experimental findings provide critical insights for achieving adaptive controls of reactive surfaces, paving the way for sustainable and scalable CO2 mineralization in subsurface mafic and ultramafic formations.
| Country | The United States |
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