Chemical and Hydrodynamic Mechanisms for Long-Term Geological Carbon Storage

Geological storage of CO2 (GCS), also referred to as carbon sequestration, is a critical component for decreasing anthropogenic CO2 atmospheric emissions. Stored CO2 will exist as a supercritical phase, most likely in deep, saline, sedimentary reservoirs. Research at the Center for Frontiers of Subsurface Energy Security (CFSES), a Department of Energy, Energy Frontier Research Center, provides insights into the storage process. The integration of pore-scale experiments, molecular dynamics simulations, and study of natural analogue sites has enabled understanding of the efficacy of capillary, solubility, and dissolution trapping of CO2 for GCS. Molecular dynamics simulations provide insight on relative wetting of supercritical CO2 and brine hydrophilic and hydrophobic basal surfaces of kaolinite. Column experiments of successive supercritical CO2/brine flooding with high-resolution X-ray computed tomography imaging show a greater than 10% difference of residual trapping of CO2 in hydrophobic media compared to hydrophilic media that trapped only 2% of the CO2. Simulation results suggest that injecting a slug of nanoparticle dispersion into the storage reservoir before starting CO2 injection could increase the overall efficiency of large-scale storage. We estimate that approximately 22% ± 17% of the initial CO2 emplaced into the Bravo Dome field site of New Mexico has dissolved into the underlying brine. The rate of CO2 dissolution may be considered limited over geological timescales. Field observations at the Little Grand Wash fault in Utah suggest that calcite precipitation results in shifts in preferential flow paths of the upward migrating CO2-saturated-brine. Results of hybrid pore-scale and pore network modeling based on Little Grand Wash fault observations demonstrate that inclusion of realistic pore configurations, flow and transport physics, and geochemistry are needed to enhance our fundamental mechanistic explanations of how calcite precipitation alters flow paths by pore plugging to match the Little Grand Wash fault observations.