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Preliminary results on comparing conceptual approach of DFN (LANL) and FCM (SNL) models

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energys National Nuclear Security Administration under contract DE-AC04-

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Hari Viswanathan, Nataliia Makedonska, Satish Karra, Jeffrey Hyman Los Alamos National Laboratory Hadgu Teklu, Elena Kalinina, Yifeng Wang, Emily Stein Sandia National Laboratories 2016 UFDC Annual Working Group Meeting Session, June, 2016 Las Vegas, NV

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DFN model

Discrete Fracture Network Fractured Continuum Model

Discrete Fracture Network Model generates fracture networks similar to those observed on natural sites using site fracture characteristics. DFN undertakes fracture percolation between boundary faces of the simulation domain. DFN provides all necessary information for FCM for the transport and flow comparison.

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DFNWorks

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dfnGen Network

Generation using FRAM

dfnFlow Flow simulation

using PFLOTRAN

dfnTrans Lagrangian

Transport using a modification of WALKABOUT

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Step 1: Generate Fracture Networks using DFNWorks

Three fracture sets are generated based on Forsmark site fracture characteristics (Table 6-75 SKB report TR10-52)

Fracture transmissivity is defined as function of fracture size

Fracture aperture is correlated to fracture size and calculated from transmissivity using cubic law

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Step 1: Generate Fracture Networks using DFNWorks

Example of DFN realization

Statistical distributions of fracture network:

Fracture Size

Fracture Aperture

Fracture Permeability

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Step 2: Mapping DFN into Continuum

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Step 2: Mapping DFN into Continuum

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The fracture network structure of

the DFN is mapped into regular voxel mesh.

Each voxel in the hexahedral mesh has dimensions of 10 m.

The list of fractures intersecting each voxel is created and passed to FCM team.

DFN team proceeds with DFN.

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Step 3: Steady State Flow Solution, PFLOTRAN

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Flow direction: West-East Pressure gradient: 103 Pa

Compare Effective Permeability of DFNs and FCM: Effective permeability of 5 realizations is in the range: DFN 3.347 e-17 4.242 e-17 m2 FCM 3.68 e-17 4.67 e-17 m2

SUCCESS !

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Step 4: Modeling Transport Using Lagrangian Particle Tracking

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3000 particles trajectories colored by their travel time in log scale

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Step 4: Modeling Transport Using Lagrangian Particle Tracking

Breakthrough curves of 5 independent DFN realizations with similar characteristics. 250.000 particles contribute to each BTC.

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Future Steps

Compare BTC with transport results of FCM model

Expect differences due to presence of matrix diffusion in FCM

model

Estimate the contribution of matrix diffusion and other processes in interface between fractures surface and rock matrix.

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Preliminary results on comparing conceptual approach of DFN (LANL) and FCM (SNL) modelsDFN modelDFNWorksStep 1:Generate Fracture Networks using DFNWorks Step 1:Generate Fracture Networks using DFNWorks Step 2:Mapping DFN into ContinuumStep 2:Mapping DFN into ContinuumStep 3:Steady State Flow Solution, PFLOTRAN Step 4:Modeling Transport Using Lagrangian Particle TrackingStep 4:Modeling Transport Using Lagrangian Particle TrackingFuture Steps