Scaling of oil recovery by spontaneous imbibition for wide variation in aqueous phase viscosity with glycerol as the viscosifying agent

Oil production by spontaneous imbibition can be the key mechanism for oil recovery from naturally fractured reservoirs. Laboratory results of oil recovery through spontaneous imbibition are commonly scaled-up to forecast oil recovery at the reservoir scale. Numerous questions arise with respect to the theory of spontaneous imbibition and valid scaling of laboratory imbibition data.Use of glycerol as a viscosifying agent for aqueous solutions has many advantages and applications. A systematic study has been made of the physical and interfacial properties of glycerol/water and glycerol/brine (synthetic seawater) solutions. The solutions were used to investigate oil recovery by spontaneous imbibition at very strongly water-wet conditions for aqueous phase viscosities ranging from 1–1650 cP.Results for aqueous/oleic liquid pairs with matched viscosities were correlated satisfactorily by the Mattax and Kyte scaling group. Data were also obtained for a wide range of unmatched viscosities. Three data sets for unmatched viscosity were obtained with oil viscosity fixed at 4, 22, or 43 cP and aqueous phase viscosity varied from 1 to 1650 cP. Use of the geometric mean viscosity in the definition of dimensionless time gave satisfactory correlation of data for brine/oil viscosity ratios of up to about 4. A slight trend of increase in dimensionless time with viscosity ratio within the correlated data became accentuated with increase in viscosity ratio above about four. Residual oil saturation attained by spontaneous imbibition showed an overall small decrease with increase in viscosity of the aqueous phase.