Imbibition plays a crucial role in shale reservoir production. Characterizing the oil–water imbibition dynamics in fracture-matrix systems remains challenging due to the complex connectivity between micro-nano pore structures and micrometer-scale fracture networks. In this study, we developed a new mathematical model for spontaneous imbibition in shale fracture-matrix systems by integrating fractal theory and dynamic contact angle effects. The proposed model extends prior work by accounting for critical factors such as gravity, osmotic pressure, slip length, and effective viscosity. Experimental validation was conducted using published core imbibition datasets, confirming the model's reliability. Additionally, numerical simulations were conducted on digital core structures with varying fracture openings and distributions, and the results show that the model better captures the imbibition patterns in matrix pores and fracture-matrix systems. Results indicate that fractures significantly enhance fluid connectivity and oil displacement efficiency, with smaller and more connected fractures leading to higher porosities and effective oil recovery. Furthermore, the dynamic behavior of the water phase and oil displacement in heterogeneous core structures was investigated, revealing the dominant role of capillary pressure and fracture connectivity in influencing imbibition efficiency.
Zhang et al. (Fri,) studied this question.
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