Role of Wettability and Interfacial Tension in Water Flooding

Laboratory water floods were performed in oil-wet and water-wet alundum and Torpedo cores, displacing a refined oil with n-hexylamine or Triton X-100 solution. Also, some flood were performed in which a sucrose solution was displaced with n-butyl alcohol. The purpose of the tests was to see if the oil recovery could be increased and to examine what role the interfacial tension reduction and wettability change play in the recovery mechanism. It was found that the chromatographic transport of amine was influenced by core wettability. In oil-wet cores, the rate of advance of the amine band could be predicted from equilibrium chromatography, while in water-wet cores the amine band moved faster than predicted, indicating a nonequilibrium process. By reducing the interfacial tension to 1.1 dyne/cm, oil recovery was increased. More oil was recovered from Dri-filmed cores than from water-wet cores. Reversing the wettability of the porous media from oil-wet condition also resulted in some additional oil recovery. Neutral wettability floods did not increase oil recovery. Introduction Interfacial forces in petroleum reservoirs are responsible for retention of large quantities of residual oil. Increasing exploration costs have created an incentive to attempt recovery of this residual oil by new and novel processes. One novel process involves changing the interfacial forces by introducing a chemical into the reservoir during water flooding. Recently, several investigators have carried out laboratory displacement tests using amines. The amines adsorbed onto initially water-wet core surfaces, changing them to oil wet. Additional oil was recovered when the cores were flooded in a manner reversing the wettability from oil-wet conditions. In all these studies, the wettability reversal was considered responsible for increased oil recoveries although it was noted that amines also reduced oil-water interfacial tension. In the present study, displacement experiments were performed in water-wet and Dri-filmed cores. The purpose was to separate the effects of lowering the interfacial tension from changing the wettability. LABORATORY STUDY All experimental data given in this paper have been obtained at a temperature of 70F +/- 1 and prevailing atmospheric pressure. FLUIDS AND MATERIALS The oil used in these experiments was washed with H2SO4 and passed through two 100–200 mesh silica-gel beds to remove unsaturates and surface active impurities. Normal hexylamine of practical purity was used, and the alundum cores were composed of nearly pure Al2O3. Fused quartz (SiO2) and Lucalox (Al2O3) plates were used in the contact angle measurements. DISPLACEMENT TESTS Displacement tests were performed in alundum and Torpedo cores. Before displacement runs, cores were acidized with 0.1 normal HCl, flushed with distilled water and fired at 1,200F to make them water wet. This procedure also reduced water sensitivity of the Torpedo cores. Oil-wet cores were prepared from water-wet cores by flowing several pore volumes of 1 per cent by weight Dri-film SC-87 solution in heptane through the cores, flushing the cores with nitrogen, evacuating, and finally heating the cores at 300F for 4 or 5 hours. Between floods, cores were cleaned by conventional procedures and treated again as above. SPEJ P. 115ˆ