Inertial forces affect fluid front displacement dynamics in a pore-throat network model

Area of Science:

• Multiphase flow in porous media
• Pore-scale physics
• Geohydrology

Background:

• Macroscopic fluid flow in porous media masks complex pore-scale dynamics.
• Continuum theories struggle with sharp interfaces and rapid pore-scale events.
• Pore-scale dynamics influence front morphology, phase entrapment, and macroscopic transport.

Purpose of the Study:

• To develop and apply a pore-throat network model quantifying interfacial dynamics at fluid displacement fronts.
• To systematically evaluate the role of inertia and boundary conditions on fluid displacement.
• To investigate the impact of pore-scale dynamics on macroscopic transport properties.

Main Methods:

• Developed a pore-throat network model representing porous media as connected pore throats.
• Formulated local force balances (inertial, capillary, viscous, hydrostatic) for each meniscus.
• Solved force balances simultaneously for the entire fluid front under flow-rate-controlled drainage.

Main Results:

• Inertial forces influence displacement patterns by affecting invasion of high-resistance throats.
• Phase entrapment (residual saturation) is largely unaffected by inertia, limiting its impact on hydrological properties.
• Interfacial jump velocities are significantly higher than mean front velocity and depend on geometry.
• Inertia increases unpredictability of interfacial jump velocities.
• Simulated capillary pressure fluctuations and waiting times follow exponential distributions, matching experimental data.

Conclusions:

• The pore-throat network model provides insights into pore-scale dynamics of displacement fronts.
• Understanding these dynamics is crucial for basic science and applications like solute dispersion and colloid mobilization.
• Inertial effects have limited impact on residual saturation and subsequent hydrological properties.