The objective of this study was to examine the feasibility of improving the performance of EOR polymers by adding surface modified silica nanoparticles (NP). The nano-polymer sols were prepared by mixing different types of surface modified silica NP and hydrolyzed polyacrylamide (HPAM) or xanthan gum (XG) solutions. It is well known that the compatibility between organic polymer-inorganic oxide filler increases when the surface of the inorganic filler is chemically modified. To generate different interfacial interactions, the silica NP were treated by chemical grafting with carboxylic acids and silanes. The properties of the modified silica NP were characterized using Fourier transform infrared spectroscopy (FTIR) and the properties of the nano-polymer sols were investigated with viscometry and ζ-potential measurements. The non-Newtonian behavior of the nano-polymer sols was represented by Oswald-de Waele model.
Areal sweep efficiency of viscous oil displacements by nano-polymer sols was measured at 25°C in a Hele-Shaw cell representing one-quarter of a five-spot pattern. The fingering patterns of all XG samples were characterized by the formation of branched structures (at earlier growth stage) which by merging and coalescing formed stable interfaces. It was the expected behavior considering the high shear-thinning strength of the XG polymer and nano-polymer sols (n values between 0.17 and 0.27). However, the HPAM solutions and nano-polymer sols exhibited different fingering patterns with tip-splitting or suppressed tip-splitting and side-branching. This difference was attributed to different interactions between the modified NP and the polymeric chains of the two polymers.
The areal sweep efficiency of the HPAM polymer solutions did not improve by the addition of any type of NP because of the reduction of the viscosity of the polymer solution and the reduction of the interfacial tension between the injection fluid and oil. However, the XG polymer solutions, modified with the addition of 1.0 and 2.0 wt.% NP provided considerably improved sweep efficiency. The results are promising and show good potential for improving the performance of polymer flooding with Xanthan gum by addition of silica NP.