Experimental Investigation of the Role of Different Clays in Low Salinity Waterflooding

Abstract

Abstract Extensive studies have demonstrated that low salinity waterflooding (LSWF) can improve oil recovery effectively, and its typical recovery mechanisms have been proposed. However, there is stilla significant debate on the functions of clay duringLSWF. This study is to identify the influence of different clays, including montmorillonite, illite, and kaolinite, in LSWF performance and their mechanisms. The zeta potentials of sand, montmorillonite, illite, and kaolinite in the presence of high salinity water (HSW)and low salinity water (LSW) with salinities of27,501 mg/Land 2,485 mg/Lwere first examined, respectively. Then, the swelling factors of the three clay minerals in the HSW and LSW were measured in succession to determine their swelling characteristics. Subsequently, coreflooding experiments were conducted usingone clay-free sandpack column and fivesand pack columnsrespectively containing 10 wt% of montmorillonite, 10 wt% of illite, 10 wt% of kaolinite,compound clays (5wt% montmorillonite + 2.5wt% illite + 2.5wt% kaolinite), and 5wt% of montmorillonite. It has been found thatLSW could generate more negative zeta potential values for sand, montmorillonite, illite, and kaolinite, which made them more water-wet and thus favor oil recovery. Montmorillonite obviously swelled in HSW, and it could further swell significantly by contacting LSW. Although illite showed some swelling in HSW, LSW could not further expand it. Kaolinite did not swell in both HSW and LSW. The results from six coreflooding experiments showed that after high salinity waterflooding, the subsequent LSWF could generally further improve the oil recovery. The sand pack columnscontaining montmorillonite showed higherincremental oil recovery during LSWF (17.42% from sand pack column with 10wt% of montmorillonite, 10.27% from sand pack column with compound clay, and 8.90% from sand pack column with 5wt% of montmorillonite). Also, LSWF could improve oil recovery for the clay-free sand pack column, the sand pack column with kaolinite, and the sand pack column with illite by 0.73%, 0.83%, and 1.03%, respectively. Therefore, clay minerals would play an important role in determining oil recovery performance duringLSWF, and the more swelling the clay in LSW, the more favor the clay in LSWF. This study proved that both wettability alteration and clay swelling could attribute to the improved oil recovery byLSWF.