Smart Waterflooding (High Sal/Low Sal) in Carbonate Reservoirs (SPE 154508)

In recent decade, low salinity waterflooding has been emerged as a prospective EOR method. Extensive laboratory research and successful field tests showed that low salinity waterflooding can improve the oil recovery from both outcrop samples (used in experiments) and reservoir sandstones. However, low salinity effect has not been thoroughly investigated for carbonates. Most recently, Saudi Aramco reported 16-18 % OOIP increase in oil recovery by low salinity waterflooding in composite rock samples from Saudi Arabian carbonate reservoirs. The objective of this work is to experimentally investigate the oil recovery potential of low salinity water flooding for carbonate rocks and to study the ion interaction with rock and wettability change using NMR. We used the Thamama formation carbonate (Abu Dhabi) and the Aalborg chalk core plugs for this study. The flooding experiments were carried out initially with the seawater, and afterwards the contribution to oil recovery was evaluated by sequential injection of various diluted versions of the seawater. The total oil recovery, interaction of the different ions with the rock, and the wettability change were studied both at room and high temperature. No low salinity effect was observed for the Thamama formation core plug at room temperature, but increase of the pressure drop over the core plug is detected. On the contrary, a significant increase in oil recovery was observed under low salinity flooding of the Thamama formation core plug at 90 CB0C. An increase in pressure drop was also observed in this case and that may be related to migration of fines or formation of emulsions. The Aalborg chalk core plugs did not show any low salinity effect, both at room and high temperature. NMR measurements showed that low salinity brine solutions affect the wettability of the Thamama formation core plugs.