Influence of fluid viscosity on mass transfer between rock matrix and fractures

Scaling of spontaneous imbibition measurements is important to characterization of wetting properties and to modelling mass transfer between rock matrix and fractures. A scaling equation proposed by Mattax and Kyte((II)), has been widely applied to prediction of field-scale oil recovery from fractured reservoirs. The scaling equation involves many assumptions including identical core sample shapes and viscosity ratios. In this paper, the effect of viscosity and viscosity ratio on rate of spontaneous imbibition is investigated. Imbibition data is reported for systems with two orders of magnitude variation in viscosity ratio. The results show;for systems of similar geometry, try, that the imbibition time is proportional to the square root of viscosity ratio. This observation combined with a new definition of characteristic length is used to define a modified scaling group which allows for differences in viscosity ratio, and the shapes and boundary conditions of the core samples.