Brine displacement studies using Berea sandstone cores were undertaken to compare the effects of alkaline and soft saline preflush systems on an equivalent basis. The alkaline chemicals used were sodium orthosilicate, sodium hydroxide, sodium silicate (2.0 ratio of SiO2/Na2O) and sodium carbonate. The soft saline solutions used ranged in concentration from 3% NaCl to 10% NaCl. The effects of the various preflush systems were measured by titration of the effluent for hardness ion levels. In some of the experiments dilute surfactant was injected following the preflush to determine the effect of surfactant on elution of hardness ions.
Results are presented which show that the highly alkaline chemicals, sodium orthosilicate and sodium hydroxide, were very effective in removing the hardness ions from connate brine. Further elution with soft brine following the highly alkaline preflush showed that essentially no ion-exchange occurred and the hardness ion level remained at zero in the effluent. This same effect was observed with the 2.0 ratio sodium silicate, but higher volumes of solution were required to reduce the hardness ion levels to zero in the effluent. With high salinity and sodium carbonate preflushes a high ion exchange peak was observed. Continued elution reduced the hardness ion levels considerably, but not to zero.