Interfacial Dilational Rheology Between Nitrogen and Aqueous Surfactant Solutions: Implications for Foam-Assisted EOR

Abstract

Abstract Foam-assisted EOR is a promising technique to meet the ever-growing global energy demand. However, foam is thermodynamically unstable because of large gas-liquid interface. The stability of foam depends largely upon interfacial rheological properties, which represent the resistance capability to disturbance. Most previous studies address limited pressure ranges, not revealing the behavior under subsurface conditions. To fill this gap, we measured the interfacial dilational viscoelasticity of (N2 + SDS (aq)) at various pressures in a high-temperature high-pressure view cell by using the oscillating-drop-profile method. The interfacial elastic and viscous moduli were studied at pressures from ambient pressure up to 26.7 MPa, temperatures of 298 K and 348 K, SDS concentrations below the CMC (0.05 mass% and 0.15 mass%) and above the CMC (0.50 mass%) and oscillating frequencies of 0.125 Hz and 0.0625 Hz, which may correspond to the low-frequency fluctuation expected during the reservoir fluids flow in porous media. The effects of pressure, temperature, SDS concentration and oscillating frequency were examined. Both elastic and viscous moduli decreased with increasing pressure, indicating weaker resistance capability to external disturbance under high-pressure conditions. At concentrations below the CMC, elastic modulus decreased, and viscous modulus increased with increasing temperature, while at concentrations above the CMC, both moduli decreased with increasing temperature. Surfactant solutions with higher concentrations had larger dilational viscoelasticity. However, once the CMC was reached and surfactant micelles were formed in the solution, a significant drop in the interfacial dilational modulus was observed. At concentrations below the CMC, both moduli increased with increasing oscillating frequency, while at concentrations above the CMC, the effect of frequency was insignificant. The expansion and compression of pendant drop during interfacial dilational modulus measurement is closely analogous to foam flow through the heterogeneous porous media. The foam interfacial dilational properties under a variety of pressure, temperature, composition, and oscillating conditions were systematically studied for the first time. The results obtained can help to advance understanding of foams stability, enhance the design of surfactant solutions and provide guide for the implementation of foam-assisted EOR.