Summary

Foam enhanced oil recovery (EOR) was introduced to improve the sweep efficiency but avoid the formation damage caused by polymers. Foam stability diminishes in environments with harsh salinity and high temperature, and when in contact with crude oil. The present study examines using mixtures of nanoparticles and viscoelastic surfactant (VES) to improve foam mobility for EOR applications.

This paper examines the stability of carbon dioxide (CO2) foam when using alpha olefin sulfonate (AOS) as a foaming agent and the change in the mobility‐reduction factor (MRF) for different foam systems that contain nanoparticles and VES. To achieve this objective, foam stability for different systems was measured at 77 and 150°F using a high‐pressure view chamber. Interfacial‐tension (IFT) measurements (in mN/m) combined with microscopic analysis were conducted to determine the effect of crude oil on different foam systems. Single‐ and dual‐coreflood experiments were conducted using Berea Sandstone and Boise Sandstone cores at 150°F. CO2 foam was injected with 80% quality in tertiary‐recovery mode. The oil recovery and the pressure drop across the core were measured for different foam systems.

Adding silica (SiO2) nanoparticles (0.1 wt%) of 140‐nm size and viscoelastic cocamidopropyl betaine surfactant (0.4 wt%) to the AOS (0.5 wt%) solution improved both foam stability and MRF. In contact with crude oil, unstable oil‐in‐water emulsion formed inside the foam lamella, which decreased foam stability. A weak foam was formed for AOS solution, but foam stability increased by adding nanoparticles and VES. In the case of AOS solutions, the IFT measurements revealed positive values for the spreading and the bridging coefficients. Hence, the crude oil spread over the gas/water interface, and lamella films were unstable because of the bridging of oil droplets. Oil recovery from the conventional waterflooding was 48% of the original oil in place (OOIP). From the coreflood experiments, AOS foam was not able to enhance oil recovery. The tertiary‐oil‐recovery factor increased by 9 and 14% of the residual oil after the waterflooding stage by adding nanoparticles and VES to the foam system, respectively. The dual‐coreflood experiments showed poor sweep efficiency during waterflooding. The addition of nanoparticles and VES to AOS foam increased oil recovery from the low‐permeability cores by 26% of OOIP.

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