Capillary Imbibition Dynamics in Porous Media

Capillary imbibition describes the spontaneous penetration of a wetting fluid into the pore spaces of a solid matrix driven by surface tension and interfacial forces. Governed in its simplest form by the Lucas–Washburn equation, imbibition dynamics depend on pore geometry, wettability, fluid viscosity and surface tension. In real porous media, factors such as heterogeneity of pore size distribution, anisotropy of pore networks, gravitational effects and reactive surface chemistry lead to deviations from the idealised model. Advances in imaging and pore-scale characterisation have revealed the existence of transition zones at the fluid front, non-piston-like displacement and the importance of micro- and nanopores in controlling overall uptake rates. Fractal approaches have offered a framework to link time-scaling exponents to complex pore geometries. Understanding capillary imbibition is critical across disciplines: it underpins oil and gas recovery from tight reservoirs, governs contaminant transport in soils, affects moisture ingress in building materials and influences CO₂ storage in subsurface formations. Integrating multiscale experiments with refined theoretical models continues to improve predictions and guide practical applications.

Research from Nature Portfolio

Recent investigations have established criteria that delineate the applicability of the Lucas–Washburn scaling law in natural porous media, demonstrating that the ratio of capillary pressure to gravitational forces (CGR number) governs when gravity may be neglected. A threshold CGR number of approximately three has been proposed below which the classical square-root-of-time relation holds without significant error, simplifying experimental design and interpretation.

Studies of gas–water imbibition in heterogeneous reservoirs have shown that traditional models overestimate both the extent and rate of spontaneous uptake. By introducing two physically meaningful parameters – a fluid factor and a reservoir factor – researchers have optimised the Lucas–Washburn framework to account for transition zones at the imbibition front and incomplete saturation. The resulting model aligns closely with laboratory measurements in complex reservoir analogues.

Capillary Imbibition Dynamics in Porous Media publication trend

The graph below shows the total number of articles in capillary imbibition dynamics in porous media across all publications each year (not limited to Nature Index journals).

Technical terms

Capillary pressure: Pressure difference across the curved fluid interface within a pore, arising from surface tension and curvature.

Contact angle: Angle at which a liquid–vapour interface meets a solid surface, quantifying wettability.

Porosity: Fraction of the total volume of a material that is occupied by void spaces.

Permeability: Measure of a porous medium’s ability to transmit fluids under a pressure gradient.

Lucas–Washburn equation: Analytical relation describing capillary-driven penetration length as proportional to the square root of time in cylindrical pores.

Sorptivity: Measure of a material’s capacity to absorb or desorb liquid by capillarity per unit surface area and square root of time.

Wettability: Tendency of one fluid to spread on or adhere to a solid surface in the presence of other immiscible fluids.

References

1. Criteria for Applying the Lucas-Washburn Law. Scientific Reports (2015).
2. Microscopic imbibition characterization of sandstone reservoirs and theoretical model optimization. Scientific Reports (2021).
3. Effect of pH on Spontaneous Imbibition in Calcareous Rocks. Water Resources Research (2024).
4. A pore-scale study on the dynamics of spontaneous imbibition for heterogeneous sandstone gas reservoirs. Frontiers in Energy Research (2023).
5. The Hausdorff Dimension and Capillary Imbibition. Fractal and Fractional (2022).
6. Capillary Imbibition in Layered Sandstone. Water (2023).