Evaluation of rheological properties and interfacial tension of polymer-surfactant mixtures

The injection of polymeric solutions in petroleum reservoirs is a supplemental method of petroleum recovery, that seeks to increase the volumetric efficiency of swept of the oil with the decrease of the mobility of the injection water1. In the contact between two non miscible fluids, superficial tensions are established, that can influence the relations between the rock and the fluids, depending on the nature of both1, 2. Thereby, due to the created capillary forces, big amounts of petroleum are left in the reservoir. The capillary forces resist to the viscous forces externally applied in such a way that the injected water no more move the petroleum. The mainly mechanism to recover this petroleum is through the reduction of the interfacial tension, using appropriate surfactants1. Therefore, the combined injection of a surfactant and a polymer can promote improvements in the injectivity and in the global recovery efficiency3. In enhanced oil recovery, combinations of polyacrylamides and many surfactants are used as effective “pusher fluids”3. Polyacrylamide (PAAm) is a water-soluble linear polymer which finds wide application in petroleum industry1. Depending on the molecular weight, its aqueous solutions can develop high viscosities, and form hydrogen bonds with a variety of compounds3. However, the polyacrylamide presents some limitations, such as low tolerance to the presence of salts, what can promote its precipitation resulting in low oil recovery efficiency1-3. The application of the polymer in emulsion can promote a larger stability, due to the presence of a surfactant