The phenomenon of immiscible fluid flow in mixed-wetted porous media has long fascinated researchers due to its prevalence in unconventional oil reservoirs and its profound implications for the spreading behavior of fracturing fluids during invasion and flowback processes. In this study, we employed the multi-component Shan-Chen lattice Boltzmann method (LBM) to investigate the complex dynamics of immiscible fluid flow within these media. To validate our numerical approach, we simulated the forced imbibition dynamics in parallel double wettability pores and compared the results with theoretical models. Our findings reveal that wetting fluids tend to preferentially invade regions of stronger wettability in porous media, especially at low capillary numbers. In contrast, subsequent fluid injection fails to invade weak-wettable areas once a breakthrough occurs in strongly wettable zones. Additionally, we identified a critical capillary number that determines the ability of injected fluids to overcome capillary resistance and flow into weakly wetted regions, thereby enhancing fluid displacement. These insights offer valuable understanding for optimizing fluid flow in unconventional reservoirs and designing more efficient porous media systems, ultimately contributing to more sustainable and effective oil recovery techniques.
Understanding the immiscible fluid flow processes (including imbibition and drainage) of multi-component systems, such as oil-water, in porous media is of paramount importance across diverse industrial and technological domains. These processes are involved in enhanced oil recovery (EOR) (Singh et al., 2019), geologic storage of CO2 (Bachu, 2008), and proton exchange membrane fuel cells (PEMFC) (Anderson et al., 2010), among other applications. The key influencing factors in these processes encompass wettability, capillary number, fluid viscosity, and pore-throat structure (Holtzman & Segre, 2015). In particular, wettability is critical in governing slow imbibition/drainage dynamics within porous media (Bakhshian et al., 2020). During imbibition processes in predominantly hydrophilic rocks, the corner flow and wetting film phenomena are commonly observed (Zhao et al., 2016). Conversely, in the case of hydrophobic rocks, typical occurrences during drainage include the Haines jump and snap-off sensations (Alpak et al., 2019). However, it is imperative to acknowledge that reservoir rocks rarely exhibit uniform wettability; rather, they often manifest a mixed-wetting state, characterized by the coexistence of both hydrophilic and hydrophobic rock surfaces (AlRatrout et al., 2018). Therefore, to comprehend microscopic mechanisms like EOR through water flooding and the spreading behavior of fracturing fluids throughout the invasion and flowback processes requires studying the impact of mixed-wettability on two-phase flow patterns.
