Study on Non-equilibrium Effects during Spontaneous Imbibition

Abstract

Spontaneous imbibition of water into the matrix blocks because of capillary forces is an important recovery mechanism for oil recovery from naturally fractured reservoirs. In modeling this process, it has been assumed classically that local equilibrium is reached and, therefore, capillary pressure and relative permeability functions are only a function of water saturation, resulting in the appearance of the self-similarity condition. In some works published in the last 2 decades, it has, however, been claimed that local equilibrium is not reached in porous media, and therefore, opposite the classical local-equilibrium/self-similar approach, non-equilibrium effects should be taken into account in modeling multi-phase flow in porous media and, in particular, for the spontaneous imbibition process. Results from laboratory works are still contradictory about the existence of such effects during the spontaneous imbibition process. In the first part of this work, existence of the non-equilibrium effects is inve...