09 Juillet – Thesis defense - Romain Aranda

14 h Full videoconferencing

Study of blocking foam flow in high permeability porous media for remediation of soils and groundwater.

During soil remediation of saturated zones, it is sometimes necessary to confine a source in order to be able to carry out an effective treatment in situ. Confinement increases the contact time between the injected chemicals and the pollutant. This thesis presents the study of the injection of liquid foam as a blocking fluid. The work focuses especially on the study of foam flow in high permeability media, as containment is particularly necessary in this type of soils where flow rates are often high.
The first step was to study the foamability and the stability of a selection of surfactants. Then, we studied foam flows in high permeability media (> 4x10-10 m²). These experiments were carried out in columns 30 to 40 cm long. We used mass balance, pressure measurement and visual observations to obtain results. Then, we studied foam flow in thin tanks 40 cm to 1 m wide. In these experiments, there was a water crossflow simultaneously to foam flow to model a groundwater flow. The observations focused particularly on the ability of the foam to divert the water flow as well as its stability over time. We used mass balance, pressure and saturation measurement, and a photographic analysis method developed specifically for this study to obtain results. Finally, we developed a numerical model to simulate the experimental results and to identify the parameters controlling the flow and stability of the foam.
The results show that alpha-olefin sulfonate surfactant is a very good candidate for generating blocking foams thanks to its high stability and foamability, and is readily biodegradable. The foam behaves like a very viscous fluid (> 1 Pa.s) in high permeability media if it is generated using a pre-generation technique. This technique consists of injecting the gas and the liquid into a low permeability medium (fine sand, sintered glass) in order to create a fine foam and then injecting it into a high permeability medium. Direct injection of gas and liquid into a high permeability medium does not generate a viscous foam. We confirmed the shear-thinning behavior of the foam in high permeability media. We demonstrated the blocking property of the foam in tanks where foam diverted the whole water flow during the foam injection. After the end of the injection, the stability of the foam is poor in the presence of a fast crossflow (10 m/day) because it decreases the concentration of surfactant until it destroys foam lamella. We showed that stability correlates with the speed of the water crossflow. After destruction of the foam, the gas bubbles trapped in the porous medium contribute to greatly reducing the relative permeability to water in the area where we injected foam. The modeling showed that the coupling of a two-phase flow model in porous media with a solute transport model for the surfactant gives results close to the experimental results (foam injection and stability).
All the results show that the use of foam as a blocking fluid in remediation of saturated soils is promising. This manuscript gives some hints concerning the industrial use of this fluid that can be difficult to control in porous media.

Event localization