Unsteady-state CO2 foam injection for increasing enhanced oil recovery and carbon storage potential

The efficiency of CO2 injection for enhanced oil recovery (EOR) and carbon storage is limited by severe viscosity and density differences between CO2 and reservoir fluids and reservoir heterogeneity. In-situ generation of CO2 foam can improve the mobility ratio to increase oil displacement and CO2 storage capacity in geological formations. The aim of this work was to investigate the ability of CO2 foam to increase oil production and associated CO2 storage potential, compared to other CO2 injection methods, in experiments that deploy field-scale injection strategies. Additionally, the effect of oil on CO2 foam generation and stability was investigated. Three different injection strategies were implemented in the CO2 EOR and associated CO2 storage experiments: pure CO2 injection, water-alternating-gas (WAG) and surfactant-alternating-gas (SAG). Foam generation during SAG experiments showed reduced CO2 mobility compared to WAG and pure CO2 injections indicated by the increase in apparent viscosity. CO2 foam increased oil recovery by 50% compared to pure CO2 injection and 25% compared to WAG. In addition, CO2 storage capacity increased from 12% during pure CO2 injection up to 70% during SAG injections. Experiments performed at high oil saturations revealed a delay in foam generation until a critical oil saturation of 30% was reached. Oil/water emulsions in addition to CO2 foam generation contributed to CO2 mobility reduction resulting in increased CO2 storage capacity with foam.