Mechanisms of Spontaneous Imbibition and Wettability Reversal of Sandstone Cores by a Novel Imbibition Agent

The basic performance of a novel high-efficiency spontaneous imbibition agent (SXJ-2) was investigated in this study. The mechanisms of spontaneous imbibition and wettability reversal of an oil-wet sandstone surface (OSS) by SXJ-2 were studied by infrared (IR) analysis, scanning electron microscopy (SEM), zeta potential determination, wetting angle experiment, and spontaneous imbibition determination in this work. The interfacial tension between oil and water for the SXJ-2 system is relatively low. SXJ-2 has a better performance than other systems in altering the surface wettability and has a higher imbibition recovery under the same time interval than the other systems. Spontaneous imbibition recoveries of cores with high permeability are greater than that of cores with low permeability for the same surfactant solution. Spontaneous imbibition recoveries decrease as the surfactant concentrations decrease, and the spontaneous imbibition recovery is the highest when the concentration is fixed at 0.5 wt %. The higher the initial water saturation the lower the spontaneous imbibition recovery is. The ultimate imbibition recoveries of cores increase with the decrease of core length. The spontaneous imbibition recovery at room temperature is higher than that at 80 °C. At the initial and later stages of imbibition, the experimental process is controlled by capillary force and gravity, respectively. While at the intermediate stage, the process of imbibition is jointly controlled by capillary force and gravity. The absorption peak at 1170 cm–1 is caused by the sulfone −SO2– stretching vibration, indicating that the surfactant molecule SXJ-2 is adsorbed on the surface of sandstone. Due to the adsorption of the surfactant SXJ-2 on the rock surface, the size of asphaltenes was reduced, rendering the solid surface more water-wet. Thus, the mechanism of the wettability reversal of the OSS by SXJ-2 was indirectly verified by IR analysis and SEM scanning.