Pore-scale study of the effect of bifurcated fracture on spontaneous imbibition in heterogeneous porous media

Fracturing is an important technique to improve the remediation of low permeability soils and heterogeneous soils, which produce a fracture system with obvious bifurcation characteristics. Understanding the interaction mechanism between bifurcated fractures and matrix can help further enhance the beneficial effect of fracturing on soil remediation. In this study, the coupled Cahn–Hilliard phase field method and Navier–Stokes equations were solved using the finite element solver COMSOL Multiphysics to capture the oil–water interface evolution during the dynamic imbibition process in a 2D realistic pore geometry with different bifurcation fracture morphologies. The results show that the spontaneous imbibition process of the single fracture model is divided into the blocking regime and the discharging regime, while an additional connecting regime exists in the bifurcated fracture model. The growing pressure near the inlet under the blocking regime and the connecting regime is responsible for the higher remediation efficiency in the left part of the matrix. Due to the snap-off phenomenon of the oil plug expelled by the bifurcated fracture, the remediation efficiency curve shows a periodic fluctuation trend. Compared with the single fracture model, the ultimate remediation efficiency in the model with a secondary fracture and that with a tertiary fracture is improved by 30% and 33%, respectively. These results shed light upon the imbibition mechanism in a heterogeneous porous media with bifurcated fracture, which can provide guidance for the development of enhancement strategies in soil remediation.