CO2 Migration in a Stratified Reservoir System under Sequestration Conditions

Abstract:

Experimental and numerical studies are presented at two different sequestration conditions, the terrestrial and the deep-sea conditions, to elucidate possible vertical/horizontal CO₂ movement in a stratified reservoir system. The CO₂-flooding experiments revealed that once CO₂ is injected into a storage formation, the vertical migration of CO₂ is driven by combination of pressure gradient and buoyancy force. The buoyancy force was significant in our experimental conditions. The dimensionless CO₂ migration rate at vertical core setting was 36% greater than that in horizontal setting under the terrestrial condition. Experiments under both reservoir conditions showed that the injected CO₂ tended to find preferential flow path (low capillary entry pressure and high-k path) and bypass the unfavorable pathways leaving the low CO₂ saturation in the low-k layers. The liquid CO₂ intruded the low-k layers more than supercritical CO₂. Multiphase flow simulations have shown that the presence of low-k layers plays a role in CO₂ storage capacity though flow perpendicular to low-k layers will deteriorate the injectivity. The CO₂ saturation increased logarithmically with the corresponding increase in permeability modification coefficient while it decreased with capillary entry pressure. The scaled CO₂ flux showed the effect of heterogeneity was greater with high gravity number (N_gr) and decreased with small N_gr as the viscous force increased. The heterogeneity of the medium as well as N_gr caused the spatial variation of pressure, CO₂ saturation and CO₂ flux.