This document discusses efforts to model groundwater flow near the Waste Isolation Pilot Plant (WIPP) salt repository using the d3f++ and PFLOTRAN codes. It summarizes work to update an existing coarse-scale model of the WIPP site to include density-driven flow and improve the mesh and parameterization. Challenges included the old mesh's irregularity and aspect ratios as well as representing an evolving water table. Both codes struggled with the original mesh. Simpler 2D benchmark problems were suggested to better compare the codes' capabilities before further work on the full basin-scale model.
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25 Basin-Scale Density-Dependent Groundwater Flow Near a Salt Repository
1. Basin-Scale Density-Dependent
Groundwater Flow Near a Salt Repository
Anke Schneider
Gesellschaft für Anlagen- und Reaktorsicherheit
Kristopher L. Kuhlman
Sandia National Laboratories
Middelburg, The Netherlands
September 5-7, 2017
Sandia National Laboratories is a multi-mission laboratory managed and
operated by National Technology and Engineering Solutions of Sandia LLC, a
wholly owned subsidiary of Honeywell International Inc. for the U.S. Department
of Energy’s National Nuclear Security Administration under contract DE-
NA0003525. SAND2017-9392 C.
2. WIPP Hydrogeology
Repository in Salado
bedded salt formation
>500-m thick salt unit
Hydrogeology of
formations above salt
Rustler Formation
Culebra dolomite
Magenta dolomite
Anhydrite
Mudstone/Halite
Dewey Lake Red Beds
Silt/sand stones + clay
Dockum Group
Silt/sand stones + clay
2
3. Rustler Conceptual Model
3
West
(Nash Draw)
East West of WIPP
Shallow units
High permeability
Relatively fresh water
East of WIPP
Deeper units
Low permeability
Saturated brine
Regional groundwater
Flow used in WIPP PA
Long-term geological
stability of salt
5. Corbet (2000) WIPP Model
5
Most of Delaware Basin
Transient Simulation
Climate variation (dry vs. wet)
14,000 y → present → 10,000 y
Model Implementation
“water table” moving boundary
model
~8700 km2 region (78 km × 112 km)
Coarse mesh (2 km square cells)
12 model layers (10 geo layers)
1,500 cells/layer
~18,000 elements total
Halite areas (low k)
Dissolution area
(high k)
6. Motivation
6
Benchmark against existing solution (Corbet, 2000)
Comparison with original model
Old mesh, model parameters & boundary conditions
Include new processes, features & data
Include density-driven flow (e.g., Davies, 1989)
Include chemistry & mineral dissolution
Investigate flow & chemistry boundary conditions
Test and update hydrogeological conceptual model
Incoporate current data: 81Kr GW age data, water level data
Comparison and Development of Models
PFLOTRAN (SNL)
Add density dependent flow
d3f++ (GRS)
7. Update of Corbet model
7
Corbet (2000): Hydraulic conductivity [m/s]
d3f++/PFLOTRAN: Permeability [m2]
8. density-driven groundwater flow
salt and heat transport
fluid density and viscosity depending on salt concentration
and temperature
porous and fractured media
free groundwater surface – levelset function
sources and sinks
transport of radionuclides
decay and ingrowth
equilibrium and kinetically controlled sorption
precipitation/dissolution
diffusion into immobile pore water
colloid-borne transport
numerics based on UG, G-CSC, Frankfurt University
finite volume methods
geometric and algebraic multigrid solvers
completely parallelized (UG: scaling invest. some 100,000 proc.)
8
d³f++: distributed density-driven flow
9. Applications of d3f++
Applications 9
Porous media, overburden of host formations
• Gorleben Site: 2D density-driven flow and RN
transport in high saline environment
• Cape Cod: 2D contaminant transport with
pH-dependent sorption
Low permeable media
• Generic German Site in clay: 3D diffusive transport
in a low permeable anisotropic clay formation
Fractured media
• Yeniseysky site: Flow and transport in fractured rock
• Äspö (URL): Flow in the repository near field
• Grimsel (URL): Colloid-facilitated transport in clay
10. WIPP Site: „Basin-Scale“ model
SNL: Data of „Basin-scale“
groundwater model after
Corbet & Knupp 1996
raster data of 10
hydrogelogic units
source:
SNL, SECOFL3D
10
d³f++
ProMesh
www.promesh3d.com
Dewey Lake/Triassic
Anhydrite 5
Mudstone/Halite 4
Anhydrite 4
Magenta Dolomite
Anhydrite 3
Mudstone/Halite 3
Anhydrite 2
Culebra Dolomite
Los Medanos Member
Forty-Niner Member
Tamarisk Member
11. unit permeability [m²]
Dewey Lake/Triassic 10-14-10-12
Forty-Niner Member 10-20-10-12
Magenta Dolomite 10-18-10-12
Tamarisk Member 10-20-10-12
Culebra Dolomite 10-17-10-11
Los Medanos Member 10-17
WIPP-Site: Prism grid, 6 layers
N
example:
Culebra Dolomite
source: Corbet 2000
182,784 prisms (2x refined) 18,000 hexahedrons SECOFL3D
50x vertical exaggeration
11
12. WIPP-Site: Initial and boundary conditions
N
closed boundaries
c=1
(saturated brine)
12
assumed
recharge rates
source:
Corbet 2000
initial condition:
water table
14,000 years ago
source:
Corbet &Knupp 1996
13. WIPP-Site: Initial and boundary conditions
N
closed boundaries
c=1
(saturated brine)
recharge 2.0 – 0.0/0.1 mm/year, c=0 / seepage
initial condition:
water table
14,000 years ago
source:
Corbet &Knupp 1996
13
14. WIPP-Site: d³f++ simulations
14
density-driven flow, fixed water table (top boundary), permeability const. (layers)
(280,000 prisms)
model time 10,000 years, computing time 15 minutes, timestep 100 years
concentration
Darcy’s velocity
16. WIPP-Site: d³f++ simulations
16
density-driven flow, free water table
level 2 (182,784 prisms)
model time 100 years,
timestep 0.005 year (levelset method)
Darcy’s velocity, water table
17. Summary and outlook
Difficulties:
non steady-state density-driven flow model
strongly anisotropic (thin layers, jumping coefficients)
free groundwater surface 8,700 km²
Current work:
BMWi-funded joint project GRUSS (GRS, G-CSC Frankfurt University)
improve grid generating/refinement
improve robustness of solvers (convergence, timesteps)
implement volume of fluid (VOF) method to speed-up free surface handling
Next steps:
increase timestep levelset method
simulation 14.000 years past
reproduction of SECOFL3D results (Corbet & Knupp, 1996)
17
18. Reactive multiphase flow and transport code for porous media
Open source license (GNU LGPL 2.0)
Object-oriented Fortran 2003/2008
Pointers to procedures
Classes (extendable derived types with
member procedures)
Founded upon well-known (supported) open source libraries
MPI, PETSc, HDF5, METIS/ParMETIS/CMAKE
Demonstrated performance
Maximum # processes: 262,144 (Jaguar supercomputer)
Maximum problem size: 3.34 billion degrees of freedom
Scales well to over 10K cores
18
21. Issues Encountered
21
Old Mesh is very coarse
PFLOTRAN and d3f++ have difficulty with mesh
Mesh violates conventions regarding
Regularity (Δz varies too much in space)
Connectivity (must build mesh “by hand”)
Aspect ratio (2 km × 2 km × 1s-100s m)
Anke (GRS): re-mesh using modern tools (LARGE)
Kris (SNL): struggle with old mesh (COARSE)
Moving water table ≠ Richards equation
Unsaturated flow parameters are guessed
Recharge applied at water table vs. applied at land surface
CFL condition requires very small time steps
Too few elements to capitalize on parallel
Smaller elements → smaller time steps!
22. Schedule
22
SECOFL3D data provided by SNL
GRS begins building d3f++ model
SNL begins building PFLOTRAN model
SNL consults
GRS builds d3f++ model equivalent to Corbet (2000)
SNL builds PFLOTRAN equivalent to Corbet (2000)
GRS ‘includes’ density-driven flow
SNL includes density-driven flow to PFLOTRAN
WIPP basin-scale model is:
Numerically difficult
Uses non-ideal mesh (pancake elements)
Has complex boundary conditions
Try benchmarking simpler (2D) problems:
Compare processes
Use PFLOTRAN QA suite problem?
Year1Year2+Year