CO2 Foam Flow Dynamics at Reservoir Conditions

Abstract

Abstract Foam is a promising technique to reduce CO2 mobility and mitigate the impacts of reservoir heterogeneity in CO2 enhanced oil recovery (EOR) and CO2 storage processes. However, the success of foam applications depends on maintaining adequate strength at reservoir conditions. Foam can breakdown in the reservoir due to surfactant adsorption, the presence of oil, and at elevated temperatures and salinities. Therefore, foam formulations must be screened to perform optimally at reservoir-specific conditions. This work presents steady- and unsteady-state supercritical CO2 foam corefloods evaluating the effects of foam quality, injection velocity, surfactant type and concentration on foam generation and strength at reservoir conditions. We also aim to reveal real-time foam displacement mechanisms with combined positron emission tomography (PET) and computed X-ray tomography (CT), high-resolution in-situ imaging technologies. Foam quality scans with a commercially available water-soluble nonionic 0.1wt.% foaming solution indicated optimal foam qualities of 80% at 180 bar (2610 psia) and temperatures of 40°C (104°F) and 60°C (140°F). Foam rate scans showed shear-thinning foam rheology at both temperatures with a more rapid reduction in apparent viscosity with increasing injection velocity at 60°C. Unsteady-state single-cycle surfactant-alternating-gas (SAG) corefloods using different surfactant types (anionic and nonionic) at variable concentrations (0.35 wt.% and 0.50 wt.%) revealed that the foam strength was not dependent on surfactant concentration for the nonionic surfactant. However, the strength of foams stabilized by the anionic surfactant were sensitive to surfactant concentration, where the higher concentration generated a stronger foam. PET/CT images acquired during single-cycle SAG and WAG corefloods revealed real-time displacement mechanisms and saturation development during dense phase CO2 foam flow at reservoir pressure. The dynamic PET/CT images confirmed foam generation and showed that the foam displacement front was more stable and piston-like, resulting in additional fluid production, compared to experiments without foam.