In this study, the
efficacy of ionic/nonionic mixed surfactant systems as a promising
chemical route toward enhanced oil recovery applications is investigated.
The critical micelle concentration of the (CTAB + Tween 60) surfactant
system was confirmed using conductivity studies and surface tensiometry.
Thermodynamic analyses revealed that both adsorption and micellization
processes in mixed surfactant compositions are more pronounced/effective
as compared to pure surfactant solutions. Addition of polymer resulted
in improved micellar stability in mixed surfactant systems by steric
interactions. Ultralow interfacial tension values were obtained for
mixed surfactant systems using a spinning drop technique. In the presence
of carboxymethylcellulose (polymer), the viscosity of surfactant slugs
are improved, leading to sweep efficiency during oil displacement
process. Viscoelasticity investigations reveal that elastic modulus
(G′) dominate over viscous modulus (G″) at an angular frequency of >1 rad/s, showing
their capability to displace trapped oil through low permeability
regions. Mixed surfactant solutions exhibit favorable sessile drop
spreading onto oil-saturated rock surfaces and alter wetting characteristics
to the water-wet state. Surfactant adsorption onto sand reduced significantly
in mixed surfactant systems. Flooding studies revealed that nearly
20% of the original oil in place was recovered by (mixed surfactant/polymer)
chemical fluid injection after a conventional secondary recovery process.
In summary, mixed surfactant + polymer fluids constitute an effective
driving fluid for the extraction of crude oil previously trapped within
mature petroleum reservoirs.