Experimental Investigation of Wettability Alteration of Carbonate Reservoirs with Nano Gamma-Alumina : Study of Forces Between Nanoparticles and Rock Surfaces

About half of oil reservoirs in the world are carbonate. Evaluation of reservoir wettability shows that they are neutrally wet to oil wet. Usually, after primary production, water injection is employed to enhance oil recovery. Amount of oil recovery from carbonate reservoirs by water injection depends on spontaneous imbibition of water through the matrix and driving out its oil portion into the fractures. However, this process is possible when the reservoir rock is water wet. Thus, regarding the fact that most of the carbonate reservoir matrix rocks are oil wet, the amount of oil recovery by water injection process is not satisfactory. Reservoir rock wettability is an effective parameter affecting the capillary pressure which itself is the driving force for spontaneous imbibition process. Thus, it is possible to enhance oil recovery from carbonates reservoirs by changing the wettability of them from oil wet to water wet. A new approach to change reservoir wettability is using nanoparticles. Regarding their size and specific properties, these particles can easily be adsorbed on small pore walls and by changing the surface energy, alter the wettability. In this study we investigated the effect of gamma-alumina nanoparticles on a sample of carbonate rock by conducting a series of contact angle tests and as a new idea we clarified the effect of gamma-alumina nanoparticles concentration on the wettability of carbonate rock by monitoring the forces between the nanoparticles and rock surface. As our results show, gamma-alumina nanoparticle in 0.5 weight percent has the highest effect on carbonate rock wettability regarding the interactions of repulsive forces and van der waals attractive forces between nanoparticles and the rock surface