Effect of wettability alteration on enhanced heavy oil recovery by alkaline flooding

Alkaline flooding is a promising enhanced heavy oil recovery method. In this paper, this enhanced heavy oil recovery method is investigated in terms of its tertiary oil recovery potential and its effects on wettability alteration of the porous medium. Core flood tests show that the tertiary oil recovery can be greater than 10% of the initial oil in place (IOIP) by NaOH-only flooding or with NaOH and Na2CO3 mixed flooding systems. Micromodel experiments show that the wettability of the pore walls in the micromodel had been changed from water-wet to oil-wet, which can block water channeling and thereby improve the sweep efficiency. In order to prove the effect of wettability alteration on the enhanced heavy oil recovery, the contact angles of the heavy oil in alkaline solution on a quartz substrate have been measured. The results show that the contact angle can change from 24 degrees, without alkali, to about 160 degrees, under the action of NaOH or Na2CO3. The wettability alteration from water-wet to oil-wet can make the heavy oil adsorb at the rock surface and block the water channel. Therefore, the wettability alteration is one of the important mechanisms for enhanced heavy oil recovery by alkaline flooding. (C) 2015 Published by Elsevier B.V.