Nonaqueous-phase liquid infiltration and immobilization in heterogeneous media : 2. Application to stochastically heterogeneous formations

• We performed a series of well-controlled laboratory experimentsinvestigating the infiltration and subsequent immobilizationof nonaqueous-phase liquid (NAPL) in saturated heterogeneousmedia. A system of two distinct aquifer zones separated by adipping interface was considered. Heterogeneity was representedby a spatially correlated random field with known geostatisticalparameters in one zone in combination with a homogenous packingof the other zone. The effects of heterogeneity on NAPL flowand entrapment in each of the two zones were investigated. Thetime-varying NAPL saturations were continuously monitored inspace and the final static entrapment–saturation distributionwas accurately measured. The immobilized-NAPL distribution contributesto plume generation from source zones. The results show thatcapillary barriers produced by the small-scale heterogeneitystrongly influenced the migration paths and the final distributionof NAPL both in space and across different saturation ranges.The NAPL was immobilized both by snap-off to discontinuous blobsand ganglia and by capillary barriers at textural interfaces.Heterogeneity generally increased entrapment, because spatialvariations in capillary properties caused NAPL to be entrappedat higher saturations. Heterogeneity in the finer formationprovided points of entry into this formation where the NAPLsubsequently could spread as the pressure built up. The NAPLwas immobilized at high saturations because high displacementpressures in the fine materials inhibited flow at low saturations.The accessibility for water flow through NAPL occurrences andthereby also the dissolution of NAPL is limited by (i) highentrapped NAPL saturations that decrease the aqueous-phase relativepermeability and (ii) the location of NAPL inside a formationwith low average permeability.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences (hsv//eng)

Nyckelord

Earth sciences

Geovetenskap

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