An Experimental Study for the Using of Nanoparticle/VES Stabilized CO₂ Foam to Improve the Sweep Efficiency in EOR Applications

CO₂ foam has been used to improve the sweep efficiency for EOR as a replacement for polymers to avoid potential formation damage. Foams degrade at high temperatures (>212°F), in high-salinity environments, and in contact with crude oil. The present work evaluates nanoparticles and viscoelastic surfactants (VES) to improve foam stability when these foams are used as EOR fluid. This study investigates the stability of alpha olefin sulfonate (AOS) foam for different foam solutions in the presence of nanoparticles and viscosifiers (VES). To achieve this objective, foam stability tests were conducted at different temperatures up to 150°F. Foam stability was studied in a high-pressure view chamber (HPVC) to find the optimal. Single and dual-coreflood experiments were conducted at 150°F to investigate the divergent ability for the foam solutions on heterogonous sandstone formations. Boise and Berea sandstone cores with permeability contrast of 10-15 were 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 measured for the different foam solutions. Adding silica nanoparticles (0.1 wt%) of size 140 nm and viscoelastic cocamidopropyl betaine surfactant (cocobetaine VES) (0.4 wt%) to the AOS (0.5 wt%) solution improves foam stability. In contact with crude oil, unstable oil-in-water microemulsion generated inside the foam lamella that decreased foam stability. A weak foam was formed for AOS solution, but the foam stability increased by adding nanoparticles and VES. From the single coreflood experiments, the oil recovery from the conventional water flooding 47% of the original oil-in-place. AOS was not able to enhance the oil recovery. No more oil was recovered by AOS foam, however, extra oil was recovered in the presence of nanoparticles (19 %) and VES (26%). The dual-coreflood experiments revealed low sweep efficiency during the water flooding as a secondary recovery. Adding nanoparticles and VES to the AOS foam system increased the sweep efficiency and increased the oil recovery from the low permeability cores. Nanoparticles and VES were able to improve the foam stability for AOS solution. Adding nanoparticles is highly recommended for EOR applications, particularly at high temperatures.