Effect of water content on features of W/O emulsion during water flooding in heavy oil reservoir: Bulk properties and mobility control characteristics

The positive role of water-in-oil (W/O) emulsion on recovering heavy oil during water flooding has started arousing attention. Whereas, few studies have focused on exploring its mobility control characteristics, which was greatly affected by water content(phi). Thus, this paper targeted the effect of water content on its bulk properties and mobility control performance. Results showed that the increase of phi weakened the emulsion stability and enlarged the droplet size. The viscosity of W/O emulsion was 1.23-16.57 times higher than that of original oil except a few cases (phi >= 50%, (gamma)over dot >= 600s(-1)), largely elevating the displacing-displaced phase mobility ratio. Besides, for emulsions (phi > 40%), viscosities exhibited the strong shear rate dependence effect, and the values of flow consistency index ranged between 0.71803 and 0.83766. More obvious shear-thinning behaviors were observed in W/O emulsions with higher phi, which made W/O emulsion exhibit a certain self-adjustment ability to plug the layer. Compared with water-only flooding, the presence of W/O emulsion significantly increased the pressure drop, suggesting the excellent performance in permeability reduction. Due to the blocking of large-size droplets, the pressure drops in the subsequent water injection stage were significantly increased for emulsions (phi >= 70%), prolonging the duration of mobility control. Meanwhile, the presence of W/O emulsion improved fluid distribution and stabilized the flood front. Emulsions forming in higher phi presented stronger ability to reduce permeability and control profile. This study is helpful to clarify the key role of W/O emulsion.