The influence mechanism and the contribution of capillary force and gravity to recovery in spontaneous imbibition in low permeability reservoirs

Spontaneous imbibition is one of the important means to enhance oil recovery in low permeability reservoirs, and it has good field application effects. Through the interfacial tension (IFT), contact angle (CA), and adsorption experiments, the effects of SDBS surfactant on IFT and reservoir wettability were studied, and the adsorption rule of SDBS at the mineral surface was obtained. On this basis, the imbibition recovery and mechanism of cores with different permeability are studied. The study showed that in low permeability reservoir, gravity and capillary force are the main controlling factors of imbibition. In the early stage, gravity determines the recovery, because the imbibition rate is 2.75 times that dominated by capillary force. The capillary force can continue to produce oil in small pores, and the imbibition time is twice that of gravity, which determines the recovery in the late imbibition stage. Therefore, the synergistic effect of gravity and capillary force can optimize the imbibition recovery, in low permeability reservoirs. When the concentration of SDBS solution is CMC (0.1%), due to the mineral interface adsorbs, the capillary force decreases by 10.76%, and the adhesion work increases by 3.42 times, resulting in a decrease in the imbibition recovery. The imbibition driving force is different for different reservoir properties, which can be adjusted by adding a surfactant to change IFT and CA.