Adsorption/desorption of Ca2+ and Mg2+ to/from Kaolinite Clay in Relation to the Low Salinity EOR Effect

The Low Salinity Enhanced Oil Recovery effect in sandstone is promoted by a wettability alteration of clay surfaces towards more water-wet conditions. The key to understand the process is obtained through a detailed chemical understanding of rock fluid interaction at the clay surfaces. Based on our recently proposed chemical “Smart Water” mechanism, the pH is the main factor influencing the wettability alteration in Sandstone reservoirs. The increase in pH has been experimentally verified to be related to Ca2+ desorption from clay surfaces due to the small concentration of Ca2+ present in the “Smart water”. In this paper, desorption of divalent cations, Ca2+ and Mg2+, from clay surfaces is studied. The experiments are performed under controlled conditions in a sand pack containing only kaolinite and quartz at different temperatures, room temperature and 130 oC. The retention of the active cations, Ca2+ and Mg2+, was measured and compared with the non-adsorbing tracer; Li+. The results show divalent cations display a high reactivity towards clay surface and that Ca2+ by far is the most reactive species. The reactivity also increases with increasing temperature.