Numerical modeling of pore-scale phenomena during CO2 sequestration in oceanic sediments

Direct disposal of liquid CO2 on the ocean floor is one of the approaches considered for sequestering CO2 in order to reduce its concentration in the atmosphere. At oceanic depths deeper than approximately 3000 m, liquid CO2 density is higher than the density of seawater and CO2 is expected to sink and form a pool at the ocean floor. In addition to chemical reactions between CO2 and seawater to form hydrate, fluid displacement is also expected to occur within the ocean floor sediments. In this work, we consider two different numerical models for hydrate formation at the pore scale. The first model consists of the Lattice Boltzmann (LB) method applied to a single-phase supersaturated solution in a constructed porous medium. The second model is based on the Invasion Percolation (IP) in pore networks, applied to two-phase immiscible displacement of seawater by liquid CO2. The pore-scale results are upscaled to obtain constitutive relations for porosity, both transverse and for the entire domain, and for permeability. We examine deposition and displacement patterns, and changes in porosity and permeability due to hydrate formation, and how these properties depend on various parameters including a parametric study of the effect of hydrate formation kinetics. According to the simulations, the depth of CO2 invasion in the sediments is controlled by changes in the pore-scale porosity close to the hydrate formation front.