Visual investigation of the effects of clay minerals on enhancement of oil recovery by low salinity water flooding

Experimental study of Low-Salinity Water flooding (LSWF) in sandstone cores by core flooding indicated the presence of fine particles of clay minerals in the effluent. Also, migration of clay particles is considered as one of the major mechanisms for improving oil recovery by LSWF. In addition, it is believed that the presence of clay minerals is one of the necessary conditions for a positive impact of LSWF because clay/crude interaction plays an essential role in the initial wettability of porous media. However, a clear role of clay minerals in this process has not been identified. The aim of this study is to investigate oil recovery enhancement by fines migration at micromodel scale during LSWF. To this end, kaolinite and sodium bentonite were utilized as migratory and swelling clays in the glass micromodel to create clayey porous media. The results indicated that when the porous medium lacked clay minerals, LSWF did not enhance oil recovery. In the clay-coated porous medium that was free of connate water, the crude oil was adsorbed on the pore surfaces, and under this condition, LSWF caused the migration of clay particles with clinging oil droplets due to the electrical double layer force, which improved oil recovery and water wetness. If the porous medium contained clay minerals and connate water, the crude oil did not stick on the pore surfaces. Hence, in both seawater flooding and LSWF, film-flow was observed, which meant that migration of fines by LSWF did not contribute to the oil recovery enhancement. Our work showed that LSWF would be effective as the secondary recovery method if polar compounds of crude oil were adsorbed on the pore surfaces, which means that the initial wettability of porous media must be mixed-wet. LSWF in the clay-coated porous media with high cation-exchange-capacity clay in the primary mode increased the interstitial velocity in some pore paths due to pore-plugging by swelling of clay and finally led to sectional sweeping.