# Immiscible fluid displacement in porous media with spatially correlated particle sizes

## TL;DR

This study investigates how spatial correlations in particle sizes affect immiscible fluid displacement in porous media, revealing that higher correlation leads to more preferential invasion and less trapping, with implications for environmental and engineering processes.

## Contribution

It provides a systematic pore-scale analysis combining simulations and experiments to quantify the impact of spatial particle size correlations on fluid displacement patterns.

## Key findings

- Increased correlation length reduces fluid trapping.
- Higher correlation leads to more asymmetric invasion patterns.
- Experimental results support simulation findings at low capillary numbers.

## Abstract

Immiscible fluid displacement in porous media is fundamental for many environmental processes, including infiltration of water in soils, groundwater remediation, enhanced recovery of hydrocarbons and carbon geosequestration. Microstructural heterogeneity, in particular of particle sizes, can significantly impact immiscible displacement. For instance, it may lead to unstable flow and preferential displacement patterns. We present a systematic, quantitative pore-scale study of the impact of spatial correlations in particle sizes on the drainage of a partially-wetting fluid. We perform pore-network simulations with varying flow rates and different degrees of spatial correlation, complemented with microfluidic experiments. Simulated and experimental displacement patterns show that spatial correlation leads to more preferential invasion, with reduced trapping of the defending fluid, especially at low flow rates. Numerically, we find that increasing the correlation length reduces the fluid-fluid interfacial area and the trapping of the defending fluid, and increases the invasion pattern asymmetry and selectivity. Our experiments, conducted for low capillary numbers, support these findings. Our results delineate the significant effect of spatial correlations on fluid displacement in porous media, of relevance to a wide range of natural and engineered processes.