RECOVERY OF LIGHT, NONAQUEOUS PHASE LIQUID FROM POROUS-MEDIA - LABORATORY EXPERIMENTS AND MODEL VALIDATION

Laboratory experiments were conducted to measure flow of a light, non- aqueous phase liquid (LNAPL or simply ''oil'') in porous media. The ob jective of these experiments was to measure oil recovery as influenced by hysteresis, the oil-water capillary fringe, and an oil seepage fac e. Oil was infiltrated and allowed to redistribute across the horizont al length of a two-dimensional tank filled with medium sand. The first experiment involved oil recovery without water pumping, while the sec ond experiment involved oil recovery with water pumping to increase th e gradient toward the recovery well. Observed oil recovery compared fa vorably with the predictions of a numerical model (ARMOS). A dual-ener gy gamma radiation attenuation system monitored oil and water saturati ons throughout the experiments, while hydrophobic tensiometers measure d the location of the air-oil table (Z(ao)). The experimental distribu tion of oil saturations suggested the need to incorporate an oil-water capillary fringe in the calculation of oil trapping in the saturated zone. Measurements of Z(ao) indicated that hysteresis influenced the l iquid saturation-pressure relationships. When the effects of hysteresi s were incorporated into the model, predicted and measured values of Z (ao) came into agreement, especially at early times during the recover y process. Experimental data also suggested the presence of an oil see page face at the pumping well, but model results were not sensitive to this factor. Oil saturation measurements at later times suggested tha t the oil may have experienced delayed yield, an effect that was not m odeled explicitly. A sensitivity analysis revealed that oil recovery p redictions were most affected by horizontal hydraulic conductivity, fl uid scaling parameters beta(ao) and beta(ow), and van Genuchten alpha, n, and S-m. Overall, the numerical model appeared to match measured d ata for oil saturation, pressure, and recovery under two sets of bound ary conditions. (C) 1997 Published by Elsevier Science B.V.