Etched glass micromodel for laboratory simulation of NAPL recovery mechanisms by surfactant solutions in fractured rock

Abstract

Fractured porous media receive less attention than classic porous media in terms of remediation processes and sui` techniques that can be applied efficiently. An etched glass micromodel was built in order to simulate a fractured bedrock. The purpose of this paper was to evaluate the feasibility of surfactant-alcohol injection to recover NAPL with this fractured glass micromodel. The influence of several parameters influencing NAPL recovery via surfactant injection were tested in the micromodel: the ratio of alcohol to surfactant, the total concentration of active matter (alcohol + surfactant), the number of pore volume injected, the direction of the injection, and the continuous or pulsed injection mode. These tests made it possible to identify the key parameters for a better recovery of NAPL in a fractured environment, which are: continuous upward injection, six pore volume of surfactant solution and a n-AmOH/n-BuOH ratio of 2.5. Micromodel experiments were compared to previous reported experiments using the same surfactant solutions injected in classical porous media. The lower capillary number being required for NAPL recovery in porous media is probably related to the better sweep and the increase in surface area available for NAPL dissolution. NAPL recovery may be improved by increasing the capillary number by increasing the injected surfactant solution viscosity with polymer or by injecting foam.