Foam propagation through soils for enhanced in-situ remediation

The use of gas-liquid foams as a means of delivering chemicals to the subsurface is being considered as an aid to in-situ soil remediation schemes involving bioremediation, chemical oxidation and soil washing. Experiments were conducted to investigate the physics of foam flow in soils and to identify parameters that are important to allow foam injection at low pressures so as to avoid problems due to channelling and soil heaving. Gas-liquid foams of quality (gas-content) ranging from 87 to 99% were flowed through soils of permeability ranging from 0.09 to 900 darcy (0.09 to 900 mu m(2)) in vertical columns 3 in. (7.6 cm) in diameter. Surfactant solutions used for foam generation included an aqueous anionic surfactant Standapol ES-2 and two ethanol-based surfactants developed for in-situ soil flushing. These foams behaved as highly viscous fluids in flowing through soils; the apparent viscosity increased with increasing soil permeability. Foams seem to break and regenerate. At steady state, there was a net accumulation of liquid in the pore space. Based on material balance calculations, liquid content in the soil ranged from 7 to 59%. This is much higher than the liquid content of the injected or produced foam. It was observed that pressure gradients for downflow were only a fraction of that for upflow. The results also suggest that low pressure gradients can be obtained by using foams of higher quality (gas content) and a foaming agent that provides good foamability but low foam stability. (C) 1998 Elsevier Science B.V, All rights reserved.