RESUMEN
The interaction between nanoparticles and polymers has been of great interest in colloidal theory and novel materials. For example, the properties of polyacrylamide solutions and gels, which are usually used for conformance control and water shut-off in oilfields, can be improved with the addition of nanoparticles. This underlying mechanism and its applicability are investigated in this paper. A strong relationship between the phase behaviors of nanoparticles in polymer solutions and their enhancement effect on the rheology of the nanocomposite polymer solutions and gels was observed. Experiment results showed that the stability of nanoparticles was dependent on several factors, including pH, salinity, and polymer type. At neutral pH conditions, the tendency of the aggregation of nanoparticles was strengthened upon increasing the salinity, polymer concentration, and electronegativity of the polymers. Rheological measurements showed that nanoparticles could improve the viscosity of polymer solutions or the fracture stress of gels only if nanoparticles were aggregated in the corresponding systems. In addition, these rheological parameters significantly increased with increasing salinity and nanoparticle concentration. As a result, the mobility ratio of polymer solutions may be increased several times by the addition of nanoparticles. Referring to the gels, their rupture pressure gradient in the ideal model was also found to increase with nanoparticle concentration. In particular, if the nanoparticle concentration was sufficiently high (reaching 2%), the formed gels would not be destroyed by the injected water, but rather functionally act as a porous medium for permeation.
RESUMEN
Ultralow oil-water interfacial tension (IFT) has provided an important basis for screening optimum surfactant formulation for improving the oil washing efficiency. Thus, it is of great significance to further investigate the selection method for surfactant systems with ultralow IFT. In this study, a selection of surfactant systems with ultralow IFT was simplified by a method of comparing the equivalent alkane carbon number (EACN) of crude oil with the minimum alkane carbon number (n min) of surfactant mixtures. The results show that the ultralow IFT can be achieved when the n min of optimum surfactant formulation is equal to the EACN of crude oil. Meanwhile, the oil washing efficiency experiments show that the oil washing efficiency increases with the decrease of IFT, and the optimum surfactant formulation with ultralow IFT has the highest oil washing efficiency. This study provides a more efficient way for selecting optimum surfactant formulation systems with ultralow IFT for improving the oil washing efficiency.