Abstract
Using low-saline water and nanofluids has been suggested as novel enhanced oil recovery methods in the oil industry over the recent decades. Previous research has shown higher recovery factor is expected during low salinity water flooding (LSWF), nanofluid flooding and the combination of these methods. However, there is an ongoing need for research into exact mechanisms and optimum salinity and nanoparticles concentration for higher oil production. The present project works to garner insight into the mechanisms behind LSWF and nanofluid flooding at microscale. Since capillary force is the major player in the fluid flow investigation at the pore scale, the interfacial tension (IFT) and wettability variation at ambient condition were analyzed.
Low-saline brines with a wide range of concentrations were prepared to measure the interfacial tension between crude oil from North Sea and brines with different salinities. The impact of salinity on fluid-solid interaction was also tested and contact angle for systems including crude oil, brine and both intermediate-wet and oil-wet substrate glasses were measured. In the next step, nanoparticles (NPs) with the concentration of 0.1 wt% were introduced to the water with different salinities and the impact of silica nanoparticles on IFT and contact angle was investigated.
The result of interfacial tension measurements showed at 5000 ppm minimum value for IFT can be achieved, this value is called optimum salinity. Regarding contact angle measurements, in the all three systems, water-wet, oil-wet and intermediate-wet system, although at specific salinities oil droplets showed less tendency to spread over the glass surface, salinity did not influence the wettability states greatly. Presence of silica nanoparticles decreased the values of IFT and contact angle enormously and shifts all three systems (water-wet, intermediate-wet, and oil-wet) towards more water-wet state.
A series of low salinity water and nanofluids injection was carried out on water-wet, intermediate-wet and oil-wet glass micromodels in the secondary mode, and it was evaluated how recovery factor at pore scale can change as a function of salinity and presence of NPs. It was also concluded that the combination of nanoparticles and low salinity water can increase the oil recovery through nanoparticles adsorption on the surface, and synergistic effect of wettability alteration and IFT reduction.