A Comprehensive Experimental Study on Immiscible Displacements in Porous Media: Effects of Capillary Forces, Viscous Forces, Wettability and Pore Geometries

Abstract

Immiscible displacements in porous media are fundamentally significant for many natural processes and industrial applications. Although extensive work has been done in this field, some limitations still exist due to the difficulty to cover the large number of influencing factors. In this paper, we present a systematic study involving the coupled influence of capillary forces, viscous forces, wetting properties and pore geometries. By microfluidic experiments with high resolutions, both residual fluid distributions and dynamical invasion processes were clearly captured and quantitatively characterized. A void-filling behavior was identified for drainage as the capillary number Ca increased. An anomalous void-leaving behavior was found for the case of imbibition with an unfavorable viscosity ratio M, representing many ribbon-like regions invaded at intermediate Ca turned to be not accessible at high Ca. A pore geometry with a large typical pore-throat ratio seemed to enhance the void-leaving behavior. During the dynamical invasion processes, an intermittency behavior was captured in the form of a fluctuation of the increasing rate of the invading saturation with time. The intermittency dynamics were most evident for drainage with an unfavorable M. A pore geometry with high porosity acted to suppress the intermittency behaviors. Our experimental results sketched out a full view of immiscible displacements in porous media under different conditions, and provided a complete dataset which could be used to test the rapid developing pore-scale models.