Wettability modification of oil-wet carbonate reservoirs using silica-based nanofluid: An experimental approach

Wettability is an important factor which controls oil recovery and fluids displacement efficiency in the porous media. Wettability alteration (WA) from strongly oil-wet towards water wet or neutral states is one of the most effective methods of oil recovery increment. Many studies have shown that nanofluid can change the wettability of rock surface towards a desirable state and base on literature structural disjoining pressure is the main mechanism of wettability alteration via nano-treatment. However, there is a lack of information regarding the impact of salinity on nanofluid performance in porous media. Therefore, in this work, the effects of salinity, nanofluid concentration and rock type (i.e. limestone and dolomite surfaces) on wettability alteration of oil wet carbonate substrates under ambient condition were investigated. For this purpose, various static and dynamic experiments including contact angle, imbibition and core flood tests have been performed. The results on contact angle measurements showed that by increasing nanoparticles and electrolyte concentration the wettability alteration from oil wet to water wet was significantly enhanced. Moreover, the wettability alteration of dolomite substrate is much more than that of limestone substrate. In the following, the impact of nanofluid on the spontaneous imbibition for strongly oil-wet carbonate cores was closely examined. Finding results showed an increase as much as 15% of oil recovery for nanofluid imbibition in comparison to that of formation brine. Final evaluation of the nanofluid treatment in terms of its effectiveness was measured by core flood experimental runs. Comparison of relative permeability curves before and after treating have outlined that after the treatment process, the relative permeability curve has shifted to the right and the water relative permeability has reduced from 0.43 mD to 0.23 mD at the residual oil saturation due to wettability alteration of rock surface from strongly oil wet to water wet state.