Mechanistic Investigation of Chemical Additives, Fines Migration, and Salt Precipitation in CO2 Storage within Saline Sandstone Aquifers

Abstract

Geological storage of carbon dioxide (CO2) in deep saline aquifers is a key strategy for mitigating anthropogenic greenhouse gas emissions. Among the available trapping mechanisms, dissolution trapping plays a critical role in long-term storage security because dissolved CO2 becomes denser than formation brine and less susceptible to buoyant migration. However, the rate of dissolution is inherently limited by interfacial mass transfer and molecular diffusion within the aqueous phase In addition, pore-scale processes such as fines migration and salt precipitation may alter pore connectivity, flow pathways, and CO2 immobilization behavior. Despite their importance, the coupled effects of chemical additives, aqueous-phase transport properties, and pore-scale formation processes on dissolution-controlled storage remain insufficiently understood. This thesis presents a multiscale investigation of chemically influenced CO2 storage in saline aquifers through integrated laboratory experiments, molecular dynamics (MD) simulations, core-flood studies, and reservoir-scale compositional modeling. Pressure-decay experiments conducted at reservoir-relevant pressures (up to ~9.5 MPa), temperatures (40 °C), and salinities (0–20,000 ppm NaCl) quantified CO2 diffusion coefficients and equilibrium solubility in water, brine, silica nanofluids, and ionic-liquid-modified systems. Increasing salinity systematically reduced both diffusivity and solubility, while selected additives enhanced transport behavior under optimized concentrations. Under supercritical conditions, amorphous fumed SiO2 nanofluid (100 ppm) increased CO2 diffusivity to approximately 2.11 × 10-9 m2 s-1, while 5 wt.% ionic liquid increased diffusivity to ~2.19 × 10-9 m2 s-1 relative to the distilled-water baseline. Experiments in glass bead-packed porous media analogues showed that effective diffusivity was reduced compared with bulk systems because of tortuosity and confinement effects, although relative additive performance trends remained consistent. MD simulations reproduced the experimentally observed effects of temperature, salinity, and pressure on CO2 transport. Diffusion coefficients decreased systematically with increasing salinity (0–5 M NaCl) and pressure (10–20 MPa), while higher temperatures (298–348 K) enhanced molecular mobility. Radial distribution function and coordination-number analyses demonstrated stronger ion pairing and solvent structuring at elevated salinity, which restricted CO2 mobility. Core-flood experiments performed in sandstone cores at 100 °C and 1355 psi (9.34 MPa) demonstrated progressive permeability reduction from 394 to 267 mD after sequential CO2–brine injection cycles because of fines migration and salt precipitation. Despite injectivity impairment, CO2 trapping efficiency increased to approximately 70–76% after drainage, indicating enhanced residual immobilization associated with pore-throat modification and flow redistribution. SEM–EDS characterization confirmed fines mobilization and halite precipitation within pore channels. Reservoir-scale CMG-GEM simulations incorporating experimentally measured diffusion coefficients showed that enhanced aqueous-phase transport accelerated dissolution rates and increased dissolution trapping efficiency from ~25% in the baseline case to ~30% in additive-enhanced systems over long-term simulation periods. Sensitivity analyses further demonstrated the influence of temperature, salinity, capillary pressure, heterogeneity, and injection strategy on long-term storage performance...