Analysis of counter-current spontaneous imbibition in presence of resistive gravity forces: Displacement characteristics and scaling

Counter-current spontaneous imbibition (COUCSI) is an important mechanism of recovery from tight matrix blocks in naturally fractured reservoirs. In this study, by means of numerical simulation experiments we show that significant differences in terms of the final recovery and imbibition rate exist between COUCSI with and without the gravity forces. A specific situation where gravity forces are resisting the process is considered. For COUCSI in presence of these forces, literature on the scaling of recovery is limited. To present appropriate scaling equations, two approaches have been examined on the main governing equation; (1) inspectional analysis and (2) applying an approximate analytical solution. The scaling equations based on the latter approach give better results than those derived from the inspectional analysis and scaling equations in the literature, as well. The new scaling equations accounting for the resistive gravity forces and relative permeability and capillary pressure properties are presented, which are consistent with the common scaling situations, as well.