Relevance of Intra-Particle Diffusion in Modelling Hydrocarbon Transport through Dual-Porosity Porous Media in the Absence and Presence of Particles Dr. Stephane Ngueleu, Prof. Peter Grathwohl, Prof. Olaf Cirpka Kananaskis, April 22, 2015
Outline Introduction Objectives Materials and Methods Results and Discussion Conclusions
Introduction (Citizen Journalist Exchange, 2013) (The Canadian Press, 2012)
Introduction (Energy Resources Conservation Board, 2013)
Introduction (Energy Resources Conservation Board, 2013)
Introduction (Energy Resources Conservation Board, 2013)
Introduction Oil Flow rate Oil mass Processes Medium type
Introduction Sorption Initial state Final state Initial state Advection Diffusion Diffusion Final state Sorption and intra-particle diffusion Pollutant Aquifer Particle particle/grain Inter-pore Intra-pore Inter-particle pore Intra-particle pore Initial state Dispersion Final state
Introduction Organic particles (size 10 µm) released from soils and tailings ponds to aquifers. Thin and mature fine tailings (approx. size < 44 µm)! (Figure from en.wikibooks.org) (Figure from www.gardguide.com)
Objectives Understand through model-based analysis: Hydrocarbon transport in saturated dual-porosity porous media Organic particle transport and its influence on hydrocarbon transport
Materials and Methods Laboratory experiments Porous medium: natural soil with the structure of a clayey sand, grain size up to 2 mm. Organic carbon content Particle density CaCO 3 ( f [weight%] [g cm -3 OC ) ] [weight%] 0.25 2.84 0.7
Materials and Methods Organic particles: natural lignite (brown coal) 60.5 weight%. f OC Fine particles d 50 = 0.8 µm Filtered particles d 50 0.45 µm Based on the size: dissolved organic carbon (DOC) d 50 : median diameter based on the number of particles
Materials and Methods Lindane (gamma-hexachlorocyclohexane): very hydrophobic in water.
Materials and Methods Sorption behaviour of lindane through batch sorption experiments Lindane (contaminant) Clayey soil (porous medium) Lignite (Organic particle)
Porous medium Materials and Methods Transport simulation through column experiments Length: 15 cm Diameter: 2.4 cm 0.05 ml min -1
Materials and Methods Injection phase Lindane alone in 0 to 60 mmol L -1 NaCl Lindane and organic particles in 0 to 60 mmol L -1 NaCl Elution phase 0 to 60 mmol L -1 NaCl 0 to 60 mmol L -1 NaCl! (Figure from en.wikibooks.org)
Materials and Methods One-dimensional transport modelling Transport of lindane alone: - Model with kinetic sorption - Model with equilibrium sorption and intra-particle diffusion Transport of lignite particles: Model with straining and attachment Straining Aquifer matrix Attachment Particles Simultaneous transport of lindane and lignite particles
Results and Discussion Equilibrium sorption of lindane Clayey soil: - Linear distribution coefficient (K d ): 3.38 ± 0.16 - Low sorption! S K d C Lkg 1 Linear model
Results and Discussion Lignite: - Freundlich distribution coefficient (K Fr ): 707 ± 18 - Freundlich exponent (1/n Fr ): 0.72 ± 0.02 - High sorption! S K C 1 Fr n Fr mg 1 1/n Fr L 1/n Fr kg 1 Freundlich model
Results and Discussion Column experiments Spatial concentration profile of lindane alone 12 16 20 14 8 pore volumes Injection stopped X [cm]
Results and Discussion Effluent chloride and lindane concentrations Kinetic sorption Porosity n 0.5 Equilibrium sorption and intra-particle diffusion n m n im 0.4 0.1 Dualporosity Ionic strength reduction (60 to 6 mmol L -1 NaCl) did not cause soil particle mobilization.
Results and Discussion Effluent lindane and organic particle concentrations d 50 < 0.45 µm Lindane without particles Lindane with fine particles (d 50 = 0.8 µm) Lindane with filtered particles or DOC (d 50 < 0.45 µm) Fine lignite particles were completely retained in the porous medium. Travel time of lindane reduced by 25% with lignite particles < 0.45 µm.
Results and Discussion Extension to 2-D transport Hydraulic conductivity (K) and flow field 10 5 K [m s -1 ] 10 7 Hydraulic gradient h 0.005
Results and Discussion Separate transport of organic particles and lindane (kinetic sorption) Contamination time [day] Concentration of organic particles [mg L -1 ] 12 Concentration of lindane [mg L -1 ] 5 ½
Results and Discussion Particles, 5 days Particles, 1 month Lindane, 5 days Lindane, 1 month C/C in
Results and Discussion Particles, 6 months Particles, 1 year Lindane, 6 months Lindane, 1 year C/C in
Z [m] Results and Discussion Transport of lindane alone with equilibrium sorption and intra-particle diffusion
Z [m] Z [m] Results and Discussion Intra-particle porosity X [m] Inter-particle porosity
Results and Discussion Lindane, 5 days Lindane, 1 month Lindane, 6 months Lindane, 1 year
Conclusions Lindane transport was represented best when accounting for intra-particle diffusion. Organic particles > 0.45 µm were strongly retained, leading to retarded contaminant transport. Organic particles < 0.45 µm (DOC) enhanced contaminant transport.
Conclusions Long term contamination can be an indication of back diffusion from intra-particle pores to inter-particle pores, not an indication of new contamination. Pollutant Aquifer Particle particle/grain Inter-pore Intra-pore Inter-particle pore Intra-particle pore Pollutant Aquifer Particle particle/grain Inter-pore Intra-pore Inter-particle pore Intra-particle pore
Supplementary Information (Roy and Dzombak, 1997)
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