Foam for Mobility Control in EOR - a Microfluidic Approach

Foam injection is one of the processes that may be used for enhanced oil recovery, in particular for gas mobility control. The work we present is focussed on understanding foam formation and foam flow at small scale in very simple model geometries. To this purpose, a microfluidic device is used to accurately control diphasic flows confined at 10 to 100 micrometer scale. The microfluidic device is made of polydimethylsiloxane (PDMS), a transparent elastomer allowing simple and fast prototyping and easy observation of flows with optical microscopy. The experimental method is based on a microsystem that first permits formation of a dispersion of very monodisperse gas bubbles in water and surfactant at a flow-focusing geometry. The flow and the behaviour of the bubbles downstream is as well observed and measured in the model geometries including chamber, channels, etc. Complete phase diagram of the foam formed is shown, from very wet to very dry (small or high gas volume fraction) and with small or large bubbles according to pressures applied of both the gas and the aqueous phase. Image analysis is used to characterize the foam structure (quality, bubble size, bubble monodispersity). A simple analysis is done to give a criterion for the foam to be formed according to geometry, surface tension and pressures applied to the fluids. First results show that in a geometry modelling two permeabilities with simple large and small channels, fluid flow may be redirected from high permeabilities areas to small permeabilities ones. Even if obtained without any oil, this observation may be compared to what happen to foam flows in fractured rocks and may explain part of the complex phenomena involved for increase oil recovery. To conclude, microfluidic tool appears as an interesting technique to characterize the behaviour of foam at the micrometric scale.