Mapping of foam mobility in porous media

We report an experimental study of the motion of foam in granular porous media using X-ray Computed Tomography. The experiments consist of the co-injection of nitrogen and a surfactant solution in natural sandstone to generate foam. When foam reaches the steady-state flow regime, we replace a fraction of nitrogen by a tracer gas with a high X-ray absorbance (Xenon). This enables us to map out the local foam mobility distribution with a high spatial resolution. The rate of change of tracer concentrations enabled us to separate the convection and dispersion effects of the tracer. The foam mobility distribution is non-uniform, contrary to current belief, and depends strongly on the flow rates of liquid and gas. In vertical experiments, foam mobility increases from the center to the boundary. Within the flow domain, the trapped foam fractions range from 15 and 67% depending on gas and liquid flow rates. Foam seems to be less mobile towards the outlet, consistently a stronger foam development.