Role of interfacial and bulk properties of long-chain viscoelastic surfactant in stabilization mechanism of CO2 foam for CCUS

CO2 enhanced oil recovery is the most realistic carbon capture, utilization, and storage (CCUS) technology to fit the green and low-carbon development concept. During CO2 injection, gas channeling is a key problem to limiting displacement efficiency, and foam has shown great advantages in sealing channeling technology. However, conventional surfactant-stabilized CO2 foam is difficult to maintain for a long time. In this paper, CO2 foam was developed with a single long-chain viscoelastic surfactant (erucyl dimethyl amidopropyl betaine, EAB). Stability mechanism and dynamic evolution of structure were studied using multiple light scattering method. Then, the aggregation and adsorption behaviors of EAB were determined by rheology experiments, dynamic light scattering, cryogenic transmission electron microscopy, and dilatational rheology. The results showed EAB has excellent CO2 foam performance, and initial volume and the half-life of foam could reach 330 mL and 272 min. Liquid drainage and bubble coalescence of foam were delayed due to the formation of viscoelastic liquid phase and interface. Liquid film thickness was maintained at about 10 um after 2 h and interfacial dilational modulus was above 25 mN/m, which showed high surface repair efficiency and liquid storage capacity. Apparent viscosity of EAB solution decreased from 89 to 15 mPa.s as the temperature increased, which accelerated the process of water evaporation and liquid drainage. Only enough EAB molecules could effectively reduce initial surface tension from 70 to 56 mN/m to ensure good interfacial properties of foam. At high salt concentration, surface adsorption process to reach equilibrium was extended from 300 to 1400 s and dilational modulus fluctuated between 5 and 20 mN/m, which indicated surface activity and surface repair ability of EAB were inhibited. This study can deepen the understanding of aggregation and adsorption behavior for viscoelastic surfactants and broaden their application in oilfield development.