Three-Dimensional Modeling of the Evaporation of Volatile Hydrocarbons FromHeterogeneous Porous Media

摘要

Lean gas injection has been considered as a process tornimprove the recovery of bypassed volatile oils from the matrixrnof fractured reservoirs. The characterization of flow and massrntransfer in fractured reservoirs is a challenging task, due to therncomplexity of the pore space, the heterogeneity in thernpermeability of the rock, as well as the complex interplayrnbetween capillary, viscous and buoyancy forces. In the presentrnpaper we study the effect of heterogeneity. We develop arnthree-dimensional pore-network simulator that accounts forrnevaporation and diffusion of the volatile liquid trapped inrnheterogeneous pore networks. A series of numericalrnsimulations are performed in common types of natural porousrnmedia.rnWe investigate the effect of permeability gradients on thernsaturation profile, the recovery rates of the trapped liquidrnclusters, the evaporation patterns and the stability of thernreceding evaporation front. The case of a negativernpermeability gradient (high permeability close to the fracture,rnlow permeability far away) leads to a stable evaporation front.rnConversely, the effect of positive permeability gradients (lowrnpermeability close to the fracture, higher permeability farrnaway) leads to a fingered pattern, that results in lowerrnrecovery times due to higher liquid saturation at the productrnsurface. The paper finds application to problems ofrnevaporation or drying of volatile liquids or other liquids fromrnporous media. These arise in enhanced oil recovery inrnfractured systems, as well as in the remediation ofrncontaminated soils.