Effects of low-salinity water on the interface characteristics and imbibition process

Spontaneous imbibition is an important recovery method of low permeability and tight reservoirs. However, the mechanism and influencing factors of imbibition on the addition of low-salinity brine are seldom studied. In this study, the effects of ion type and concentration on the interfacial properties and the oil recovery of imbibition with low-salinity water were investigated by measuring the oil-water interfacial tension, contact angle and recovery of imbibition. The effects of temperature, pressure and other factors on the imbibition recovery under low-salinity conditions were analyzed. The results showed that the oil-water interfacial tension gradually increased with decreasing salinity of solutions at low salinity conditions, among which Ca2+ had the greatest influence on the oil-water interfacial tension. With decreasing salinity, the contact angle decreased. The contact angle showed the largest variation (22.14°) during the dilution process of formation water. The solutions of different ion types showed a different production rate and oil recovery by imbibition, among which the NaCl solution with a concentration of 5000 mg/L had the highest oil recovery. Moreover, the oil recovery of imbibition increased with increasing temperature. Compared with low pressure, the production rate in the early stage under high pressure conditions was obviously improved. With increasing pH value, the oil recovery also increased.