Project Details
Projekt Print View

Characteristics of displacement fluid fronts - from rapid interfacial jumps to steady capillary flows

Co-Applicant Dr. Peter Lehmann
Subject Area Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
Term from 2008 to 2015
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 66234063
 
Final Report Year 2017

Final Report Abstract

The predictions of drainage rates and the spatial and temporal distributions of fluid phases in porous media are of practical interest in many natural and engineering applications. In this project we developed a quantitative framework to predict drainage rates of liquid trapped behind a fast displacing front. For that purpose we simplified the representation of drainage processes in porous media by distinguishing two regions according to the dominant invasion mechanism: (i) a transient region along the displacement front where pores drain rapidly by piston-like invasion events and (ii) a region behind the front with water retained in crevices of the pore space with viscous corner flow. In a first study we expressed the amount of retained liquid as a function of drainage rate at the macroscale using the hydraulic functions of the porous media. To establish a better understanding of the processes at the pore scale, we imaged the liquid arrangement behind the front and could show that the fast draining pores become disconnected at a critical water content. This critical water content for the transition from fast drainage dominated by piston flow to steady water flow along corners is also important for the cessation of solute diffusion and attainment of field capacity and can be predicted using concepts of percolation theory. To predict drainage rates of processes controlled by corner flow we applied the foam drainage equation and established it as an alternative to Richards equation. The dynamics of the foam drainage equation evolve directly from capillary channel cross sectional geometries, linking the scales between pore scale mechanism and macroscopic flow without formulation of unsaturated hydraulic conductivity functions. To assign a representative channel network to a porous medium, we proposed a star shaped pore cross section that reproduces both macroscopic and pore scale properties. We applied the foam drainage formulation to simulate fluxes in homogeneous and heterogeneous media. Studies on transport of colloids and pathogens in crevices of the pore space with foam drainage equation will follow, where the FDE is in advantage compared to macroscopic approaches because it incorporates the corner flow and interfacial geometries that control the mobilization and velocity of such particles.

Publications

 
 

Additional Information

Textvergrößerung und Kontrastanpassung