WETTABILITY OF POROUS-MEDIA AFTER EXPOSURE TO SYNTHETIC GASOLINES

The wettability of a porous medium plays a critical role in the capill ary phenomena governing the migration of a nonaqueous-phase liquid (NA PL) and subsequent efforts to recover this type of pollutant source fr om the subsurface. Although it is usually assumed that water-wetting c onditions occur, limited field evidence at NAPL sites suggests that we ttability characteristics can change to intermediate or organic-phase wetting, especially for complex NAPL's containing polar or surfactant molecules. The focus of this work was an assessment of potential wetta bility conditions for quartz mineral surfaces after exposure to synthe tic gasolines. Many of the chemicals added to gasoline to increase eng ine performance have polar or surfactant characteristics. It is hypoth esized that these additives could sorb to the quartz, causing the surf ace to become less hydrophilic. Four gasoline additives were added to isooctane, the base chemical for the synthetic gasoline. Following the exposure of the mineral surfaces to the organic phases, wettability w as measured by three different techniques: oil-water contact angles, a ir-water imbibition rates and oil-water capillary pressure curves coup led with calculation of the USBM wettability index. Results show a cha nge to intermediate-wetting conditions for two of the additives consid ered. Both concentration and the molecular structure of the additives affect the extent of these alterations.