Gas mobility control in EOR
Gás mobility control
The high mobility of the gas combined with its low density leads it to flow through the high permeability zones of the porous medium, creating preferential channels. Foams have been used to control this high gas mobility in enhanced oil recovery since the apparent viscosity of the foam is greater than the viscosity of its components. In this way, with the foam, it is possible to access the areas of low permeability, increase the oil displacement area and consequently increase the efficiency of the process.
Rheological properties of surfactant solutions
Several challenges limit the generation and stabilization of foams that are successful in enhanced oil recovery (EOR). Three mechanisms are fundamental for the destabilization of a foam: -Coalescence – the fusion of the gas bubbles that separate; -Ostwald ripening – gas diffusion from Smaller bubbles to larger bubbles and / or to the atmosphere; -Drainage – Drainage of the solution by gravity. To assist in the stabilization of a foam a viscous aqueous phase can be used to slow the drainage of the solution and after coalescence and gas diffusion. This viscous aqueous phase can be formed by wormlike micelles. They are micelles formed by a cylindrical body with hemispherical tips.
Switchable surfactants exhibit reversibility in various properties including solubility, surface tension and viscosity, which respond to external stimuli including pH, dissolved carbon dioxide level, light, temperature and magnetic field. Some amine surfactants can be switchable from the nonionic state to cationic state when dissolved in an aqueous phase under acidic pH conditions and return to the nonionic state under basic pH conditions. Literature report that this class of surfactants can change the morphology of spherical micelles to wormlike micelles by dissolving carbon dioxide gas to lower the pH, resulting in increase viscosity of the aqueous phase.
Monitoring of bubble size distribution in bulk foams as a function of time to evaluate the mechanisms of lamellae destabilization on foam stability.