FLOW AND ENTRAPMENT OF DENSE NONAQUEOUS PHASE LIQUIDS IN PHYSICALLY AND CHEMICALLY HETEROGENEOUS AQUIFER FORMATIONS

The migration and entrapment of dense nonaqueous phase liquids (DNAPLs ) in aquifer formations is typically believed to be controlled by phys ical heterogeneities. This belief is based upon the assumption that pe rmeability and capillary properties are determined by the soil texture . Capillarity and relative permeability, however, will also depend on porous medium wettability characteristics. This wettability may vary s patially in a formation due to variations in aqueous phase chemistry, contaminant aging, and/or variations in mineralogy and organic matter distributions. In this work, a two-dimensional multiphase flow simulat or is modified to simulate coupled physical and chemical formation het erogeneity. To model physical heterogeneity, a spatially correlated pe rmeability field is generated, and then related to the capillary press ure-saturation function according to Leverett scaling. Spatial variabi lity of porous medium wettability is assumed to be correlated with the natural logarithm of the intrinsic permeability. The influence of wet tability on the hysteretic hydraulic property relations is also modele d. The simulator is then employed to investigate the potential influen ce of coupled physical and chemical heterogeneity on DNAPL flow and en trapment. For reasonable ranges of wettability characteristics, simula tions demonstrate that spatial variations in wettability can have a dr amatic impact on DNAPL distributions. Higher organic saturations, incr eased lateral spreading, and decreased depth of infiltration were pred icted when the contact angle was varied spatially. When chemical heter ogeneity was defined by spatial variation of organic-wet solid fractio ns (fractional wettability porous media), however, the resultant organ ic saturation distributions were more similar to those for perfectly w ater-wet media, due to saturation dependent wettability effects on the hydraulic property relations. (C) 1998 Elsevier Science Limited. All rights reserved.