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 s chemes 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 inje ction at low pressures so as to avoid problems due to channelling and soil heaving. Gas-liquid foams of quality (gas-content) ranging from 8 7 to 99% were flowed through soils of permeability ranging from 0.09 t o 900 darcy (0.09 to 900 mu m(2)) in vertical columns 3 in. (7.6 cm) i n diameter. Surfactant solutions used for foam generation included an aqueous anionic surfactant Standapol ES-2 and two ethanol-based surfac tants developed for in-situ soil flushing. These foams behaved as high ly viscous fluids in flowing through soils; the apparent viscosity inc reased with increasing soil permeability. Foams seem to break and rege nerate. 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 co ntent of the injected or produced foam. It was observed that pressure gradients for downflow were only a fraction of that for upflow. The re sults also suggest that low pressure gradients can be obtained by usin g foams of higher quality (gas content) and a foaming agent that provi des good foamability but low foam stability. (C) 1998 Elsevier Science B.V, All rights reserved.