The practice of injecting CO2 for oil production was initiated in the 1950's. Today, CO2 flooding is an established technique to enhance oil recovery (EOR), and CO2 capture and storage in deep geologic formations is being studied for mitigating carbon emissions. CO2-foam has been used to improve the sweep efficiency as a replacement for polymers to avoid formation damage. Although it is common to use surfactants to generate and stabilize foams, they tend to degrade at high temperatures (212°F), high-salinity environments, and in contact with crude oil. Adding nanoparticles is a new technique to stabilize CO2 foams. The present work evaluates new foaming solutions that incorporate nanoparticles and viscosifiers to investigate the mobility-control performance when these foams are used as EOR fluids.
This study investigates the stability of alpha olefin sulfonate (AOS) foam and the corresponding mobility-reduction factor (MRF) for different foam solutions in the presence of nanoparticles and viscosifiers. To achieve this objective, foam stability was studied for various solutions to find the optimal solution at which higher foam stability in the CO2 foam system can be reached. Coreflood tests were also conducted on different Buff Berea sandstone cores at 150˚F saturated initially with a dead crude oil. The CO2 foam was injected with 80% quality as tertiary recovery mode. The oil recovery and the pressure drop across the core were then measured for different foam solutions.
Adding silica nanoparticles (0.1 wt%) and viscoelastic surfactant (VES) (0.4 wt%) to the AOS (0.5 wt%) solution improves both foam stability and MRF. In contact with crude oil, unstable oil-in-water emulsion formed inside the foam lamella that decreased the foam stability. A weak foam was formed for AOS solutions, but the foam stability increased by adding nanoparticles and VES. The oil recovery from the conventional water flooding (as a secondary recovery before foam injection) ranged from 40 to 48% of the original oil-in-place. AOS was not able to enhance the oil recovery with an apparent viscosity similar to that for the water/gas system (with no AOS in the solution), and no more oil was recovered by AOS foam. The addition of nanoparticles and VES to the solution improved the foam MRF and allowed extra oil production (8% in presence of nanoparticles, 15% by adding nanoparticles and VES).