Dynamic capillary effects in water-wet low-permeability porous media during forced imbibition

Dynamic capillary pressure plays a critical role in understanding fluid displacement in low-permeability reservoirs, particularly under non-equilibrium conditions during forced imbibition. This study introduces a novel experimental apparatus and methodology to quantify dynamic and quasi-static capillary pressure behaviors in water-wet porous media. Core samples from a low-permeability water-wet reservoir were subjected to varying injection rates, permeability ranges, and oil–water viscosity ratios using brine and crude oil as the fluid pair. Key findings reveal that dynamic capillary pressure (Pcd) consistently lies below quasi-static capillary pressure (Pcqs) across all experimental conditions, with the gap increasing under higher injection rates. Notably, negative Pcqs and Pcd values were observed during forced imbibition, a unique phenomenon warranting further investigation. Dimensionless analysis and curve fitting yielded a quasi-dynamic coefficient model that captures the transient capillary effects as a function of permeability, viscosity ratio, and injection velocity. The model demonstrated high accuracy (R2 ≈ 0.85) in predicting dynamic capillary pressure behavior. Experimental and fitted results highlight the significant influence of displacement velocity on dynamic effects, with stronger effects observed in low-permeability samples. This study advances the understanding of capillary pressure dynamics in low-permeability systems, providing a robust framework for improved reservoir simulation and enhanced oil recovery strategies.