Experimental investigation of the role of different clays in low salinity waterflooding

Abstract

Various studies have demonstrated that Low Salinity Water Flooding (LSWF) can enhance oil recovery effectively, and its typical recovery mechanisms have been recognized. However, there is still a significant debate on the functions of clay during LSWF. This study investigates the impact of different clays, including montmorillonite, illite, and kaolinite, on the performance of LSWF. The zeta potentials of sand, montmorillonite, illite, and kaolinite in the presence of high salinity water (HSW) and low salinity water (LSW) were first examined. 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 using one clay-free sand pack column and five sand pack columns respectively containing 10 wt% of montmorillonite, 10 wt% of illite, 10 wt% of kaolinite, compound clays (5 wt% of montmorillonite + 2.5 wt% of illite + 2.5 wt% of kaolinite), and 5 wt% of montmorillonite and the cumulative oil production and pressure drops were recorded. A produced crude oil sample with the American Petroleum Institute (API) gravity of 34° and viscosity of 14 cP (60°F) was used in the experiments. The total dissolved solids (TDS) of the HSW and LSW are 27,501 mg/L, and 2,485 mg/L respectively. It has been found that LSW 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 columns containing montmorillonite showed higher incremental oil recovery during LSWF (17.42% from sand pack column with 10 wt% of montmorillonite, 10.27% from sand pack column with compound clay, and 8.90% from sand pack column with 5 wt% 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 in LSWF, and the more swelling there is in clay in LSW, the more favorable it is in LSWF. This study proved that both clay swelling and wettability alteration could attribute to the improved oil recovery by LSWF.