Tuning capillary flow to enhance immiscible fluid displacement

Immiscible fluid displacement in rock, ceramic, and other porous materials is fundamental to many applications, from groundwater remediation and enhanced oil extraction to fuel cell operation.

One challenge in making such applications more effective is increasing the stability between two fluids, so there is no mixing or other undesirable consequences. Through numerical modeling, Si Suo and Yixiang Gan address this problem by adjusting the solid material’s pore geometry to create ordered, hierarchical structures.

As one fluid, such as water or solvent, displaces another of higher viscosity, such as oil, fingerlike patterns begin to form, causing interfacial instability. Reducing these “fingerings” would increase the uniformity of the injected liquid to enhance permeability.

The researchers focused on fingerings produced by the capillary force from one pore to the next at the molecular level, which is affected by surface tension. As the invading fluid advances, it uses the minimum amount of capillary pressure to permeate each pore in a percolationlike process that results in uneven distribution.

To reduce the capillary effects by orders of magnitude in the solid base material, the researchers introduced a second-order pore structure, which increased the number of pore spaces.

“Our results suggest that with a higher porosity of the second-order porous structure, the displacement can keep compact across a wider range of wettability conditions,” Gan said.

The research could contribute to new material design and the development of microfluidic devices used to better investigate field-scale applications. Researchers plan to validate their theory with lab and field-scale experiments for specific applications.

Source: “Tuning capillary flow in porous media with hierarchical structures,” by Si Suo and Yixiang Gan, Physics of Fluids (2021). The article can be accessed at https://doi.org/10.1063/5.0038634 .