An experimental study on the imbibition characteristics in heterogeneous porous medium

Abstract

Capillary imbibition plays an essential role in the flow behavior of unconventional reservoirs. The severe heterogeneity of pore structures in unconventional formations can lead to different imbibition processes and flow dynamics compared to conventional reservoirs. This study investigates the imbibition process in heterogeneous pore networks by first examining the imbibition process between different pores using an ideal capillary model with interacting microchannel micromodels. The results reveal that water preferentially imbibes into small microchannels rather than large ones, and the imbibition velocity decreases with the microchannel width due to crossflow between different microchannels. Furthermore, heterogeneous matrix–fracture micromodels are used to examine the influence of boundary conditions, pressure conditions, and pore structure distribution on the imbibition process. The results show that the imbibition pattern is primarily governed by the boundary condition and is unaffected by the driving pressure condition. The conventional dimensionless time model fails to capture the spontaneous imbibition characteristics due to the interaction of different pores and the change in the imbibition pattern. Both increasing the injection pressure and increasing boundary openness can lead to higher oil recovery enhancement, and the distribution of the pore structure also influences the final oil recovery. Finally, the imbibition characteristics in the core scale are monitored using Nuclear Magnetic Resonance, demonstrating the similar phenomenon that water can imbibe into small pores and displace oil into larger pores. These findings enhance our understanding of the imbibition mechanism in heterogeneous porous media.