Wettability Alteration of Carbonate Rocks by Polyelectrolyte Complex Nanoparticles

Abstract

More than fifty percent of oil reservoirs around the world are carbonate reservoirs. Oil recovery from carbonates requires closer attention due to the heterogeneity of the rock and its wettability system. A majority of carbonates are considered to be mixed-wet to oil-wet. Changing oil-wet systems toward more water-wet is a key factor for improving oil recovery efficiency. Recently, investigations for the optimum methods of wettability alteration, particularly in carbonates, have attracted the attention of researchers in the area of enhanced oil recovery. There are several methods for wettability alteration that have been used by the industry, including the usage of different chemicals such as surfactants or low salinity fluids. Using nanoparticles for alteration of wettability is a new and promising method that has more focus now in the industry due to its novel and unique properties. In this research, a Polyelectrolyte Complex Nanoparticle (PECNP) was synthesized in the lab in order to investigate and evaluate its ability of wettability alteration for limestone carbonate rocks. The effect of wettability alteration was investigated by measuring oil/brine interfacial tension, contact angle, and by conducting Amott test. In addition, core flooding experiments were performed using different schemes of injection by altering between nanoparticles and different brine systems. The results showed that the PECNP system could change the wettability of the rock towards a more water-wet condition. The PECNP system was able to reduce the brine/oil interfacial tension significantly to very low values reaching 2 dynes/cm. Overall, it is concluded that PECNP can be effective as an enhanced oil recovery agent.