FEFLOW_Conference_HydroGeoBuilder_final (HESCH 2009).pdf
Transcript of FEFLOW_Conference_HydroGeoBuilder_final (HESCH 2009).pdf
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Conceptual Model Development forMODFLOW or FEFLOW modelsFEFLOW Conference
September 2009
Wayne Hesch
Schlumberger Water Services
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OutlineIntroduction
What is a conceptual model
Groundwater modeling workflows
Numerical modelingConceptual modeling
Benefits of Conceptual Modeling
Future Development
Questions
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IntroductionIn order for a groundwater model to be accurate, reliable, and
robust, it requires a tremendous amount of information and
understanding of the aquifer.
The first step in developing a groundwater model, and perhapsthe most important, involves the design of a conceptual model
Conceptual modeling is often overlooked => modelers
constrained by selected simulator, and/or a specific numericalgrid or mesh
Conceptual modeling can lead to more efficient model
development, and opportunity for multiple interpretations and
multiple discretizations.
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Build a Conceptual Modela conceptual model is a hydrogeologists mental representation
of the groundwater flow system
always sketch the system and augment this representation with:distribution of hydrogeologic layers,location of boundaries,
2D/3D representation of the domain,
plan vs. cross-sections,
tables of parameter input values,
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Conceptual Model: Definitions
A conceptual model is a simplified, high-level representation of
the site to be modeled
The conceptual model represents our best idea of how the
aquifer works.A conceptual model is a basic graphical representation of a
complex natural aquifer system thatcan more easily be
adjusted prior to dedicating the effort in developing thenumerical model.
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Why Create Conceptual Models?
Simplify the field problem
Organize field data so that the system can be analyzed more
easily
The closer the conceptual model approximates the field
situation, the more accurate is the numerical model
Strive for parsimony simplest is best, but retain enough
complexity to adequately reproduce the system behaviorFailure of numerical models to make accurate predictions
can often be attributed to errors in the conceptual model
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Numerical Model Development
the conceptual hydrogeologic model is the most important step
in groundwater model process
it forms the basis for developing the numerical model
an increased level of effort in creating the conceptual modelreduces the effort calibrating the numerical model
Level of Effortonceptual
Model
Numerical
Model
Everything should be made as simple as possible but not simpler.
Albert Einstein
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Developing a good conceptual model requires you to
compile detailed information ongeologic formations
groundwater flow directionshydrologic boundaries (recharge, rivers, lakes, wetlands, )
hydrogeologic parameters (conductivity, storage, porosity, )
extraction or injection from wells (location, depth, screens,
rates), and
observations of groundwater head and water quality
Conceptual Model
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vast amounts of data generated from numerous
sources in a variety of formatsField, Analytic, Spatial
Eg: GIS, CAD, Gridded files, spreadsheets, databases
added complexity of multiple projects and changing
conditions over time
determining which data is needed for the groundwater
model
gathering the required data from other applications in
the correct format to import into the modeling software
package
Conceptual Model Challenge
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The Groundwater Modeling Process
Build Conceptual Model
Assign Model Parameters
Collect Data
Design Model Grid/Mesh
Assign Boundary Conditions
Define Objectives
Yes
No
Predictive Simulations
Post Audit?
Calibrate and Validate Model
Sensitivity Analysis
Suitable?
Yes
No
Suitable?
Yes
No
Suitable?
Yes
No
Suitable?
Af ter Anderson & Woessner (1982)
Conceptual
Modeling
Numerical
Modeling
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Traditional Approach - Numerical Modeling
with numerical modeling designing the grid/mesh is the first
step
the disadvantages of this approach include:The correct grid/mesh must be generated before assigning properties,
boundaries, wells, etc.
If the grid/mesh is modified after other inputs
are defined, you will need to check and
re-work those input elements, to see thatthey are still in the appropriate location
Generally the input elements are not easily
modified, typically you need to delete them
and then re-assign them
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Numerical Modeling Workflow (FEFLOW)
model?
Ano
ther
Define Numerical Model
Develop mesh
Define the Property Zones Define Boundaries (rivers, wells,, )
Define SuperElement Mesh
Define 2D Mesh
Define Slice Elevations
Input Data
Import shapes, wells, surfaces,XYZ points, cross-sections
Digitize new GIS layers
Define Property Zones
Define Flow Boundaries
Run Simulation
Analyze Results
Run FEFLOW
Check (visualize) results
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Conceptual Modeling
with conceptual modeling, designing the gridor mesh is the last step
Advantages:
define the conceptual model boundary, and model inputs independent ofany numerical grid or meshprovides the freedom to design multiple conceptualizations of your site,and easily change your conceptual modeldefine multiple grids or mesh types, each with different resolution and
size, and choose the most appropriate onetransfer the conceptual model, and the desired numerical grid/mesh, tothe numerical modelAbility to change the simulator, based on the project needs
all model inputs including properties, wells, and boundary
conditions are assigned to the selected grid/mesh automaticallyresulting MODFLOW or FEFLOW input files are generated
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Conceptual Modeling
other advantages:if you are not happy with the grid/mesh, you can design a new one and
re-generate a new numerical model using this new grid
this flexibility is not possible with classical numerical modeling, as itwould require you to build and manage multiple numerical models
Easily change your model after it is createdraw data are left in tact and grid/mesh-independent
Easily expand size of the model domain, vertical discretization, and the
model inputs can be easily regenerated from the conceptual objects
if the project objectives change, a new numerical model can be easily
generated, or existing ones updated, from the conceptual objects
it allows for translating the conceptual model to FEFLOW or MODFLOW,
with vertical layers that follow the geology or are layer-independent
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Workflow: Data Conceptual Numerical
Run Simulation
Analyze Results
Load the files into VMOD/FEFLOW to
run the simulation Load results into Hydro GeoBuilder for
visualization and interpretation
Numerical Model (MODFLOW/FEFLOW)
Apply a grid/mesh Assign the conceptual model to the grid Create input files for the simulator
(MODFLOW/FEFLOW)
Finite
Differences
Finite
Elements
Input Data
Import shapes, wells, surfaces,
XYZ points, cross-sections Digitize new GIS layers
Structure
Define Conceptual Model
Define the Geology: Coverage and Horizons
Define the Property Zones
Define Boundaries (recharge, pumping wells)
Properties
Boundary Conditions
Define Model Domain
Define the region where you want to
run a model simulation
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Conceptual Model Structure
define horizons from surfaces
horizon truncation rule determines
hierarchy; in case of intersections,which will be pushed up/down, or be
truncated by surfaces above/below
several horizons types accommodate
various geological conditions(pinchouts, discontinuous layers)
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Conceptual Model: Generating Geologic Model
Define surfaces
by interpolating XYZ points
from well unit contacts
from cross-sectionsImporting .DEM, .GRD, etc.
Convert to horizons
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Conceptual Model: Generating Geologic Model
load fence diagrams, cross-sections
interpolate contact points to create surfaces
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Conceptual Model Structure: Benefits
Model AreaEasily modify the size of the model
=>Re-generate superelement mesh and slices
=>Re-translate .FEM file input.
HorizonsUse native file formats to define surfaces, and resulting horizons
(.XLS, XYZ points, ESRI .GRD, Surfer .GRD, cross-sections)
Horizon rules simplifies modeling of complex geology
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Conceptual Model: Property Zones
use shapefiles (*.SHP) or CAD polygons to define property zones
several methods for defining property zone values:constant value (by layer)
Use shapefile attributes2D interpolated surface (2D Grid)
use 3D Gridded Data
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Conceptual Model Properties: Benefits
Flexible units for flow materials
Various methods for defining input
Not assigned to a mesh/gridIf mesh changes, can easily re-generate FEFLOW input fromconceptual model
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Conceptual Model: Boundary Conditions
use shapefiles (*.SHP) or CAD polygons/polylines to define
boundary geometry and attributes
several methods for defining boundary conditions:
constant valueuse Surface (river stage from DEM)
use time schedule
use shapefile attributes
Assign values to entire zone or vertices on lines (eg. Rivergauging stations)
Assign geometry to side faces of model domain
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Conceptual Model Boundary Conditions: Benefits
Flexible units for flow rates, heads, etc
Various methods for defining input
Work with combination of data objects and operationsminimized pre-processing in GIS
Not assigned to a mesh/gridIf mesh changes, can easily re-generate FEFLOW input from
conceptual modelCan move boundary objects (eg. Groundwater divide)
Pumping wellsScreen locations and pumping rates are mesh-independent: if mesh
changes, FEFLOW input can be easily re-generated
During translation to .FEM file:well screens are assigned between appropriate slices
flow rates are distributed accordingly for multi-layered wells
(no need to assign wells on layer-by-layer basis)
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Define Numerical ModelSelect simulator and define appropriate grid or meshMODFLOW
Define horizontal grid resolution, rotationRefine grid, or define local gridsDefine vertical layers
Use HorizonsIndependent of geology
FEFLOWDefine superelement meshDefine 2D Horizontal meshDefine 3D Slice elevations
Using Horizons
Independent of geology
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Benefits of Grid/Mesh Generation
Deformed layer elevations automatically taken from
conceptual model
Generate model layers independent of the geologic structureMin layer thickness enforced, in pinchout regions
Advanced vertical refinement
Iterative approach
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From Conceptual Model to Multiple Numerical grids with
MODFLOW properties
Property zones in the
conceptual model
Semi-uniform Grid
deformed top and bottom
layers, uniform in middle
Useful for discontinuous layers
(common in unconsolidated
aquifers)
Uniform Grid
Flat layer top/bottoms
Fully respects FD assumptions
More layers, but useful for
transport/density dependent
simulations
Deformed Grid
Layers follow geology
Easy, few layers
Problems with pinch-outsand cell aspect ratios
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From Conceptual Model to Multiple Meshes
Property zones in the conceptual model
Semi-uniform
deformed top and bottom layers
uniform in middle
Property upscaling is applied
Useful where Deformed mesh fails
Deformed Mesh
Layers follow geology
Easy, few layers
Convergence issues with tight
geometry/water table fluctuations
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Property Translation
With numerical modeling, properties in pinch out layers have to
be assigned manually.
With conceptual modeling, properties are assigned to 3D
Volumes.During translation, for layers that pinch out, the properties are
automatically assigned from layers above/below (depending on
minimum layer thickness and horizon rules)
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Property Upscaling:
Algorithm to Satisfy Darcys Law on Element Level
For each finite elementCalculate all property zones intersected by the element (even the thinnest
ones are taken into account)Upscale horizontal conductivity using parallel connection rules
Upscale vertical conductivity using sequential connection rules using a
weighted average of zone values intersected by finite element
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Numerical Property Upscaling
Zone lines
Grid lines
Zone=1
Zone=2
Zone=3
1 2 3
4 5 6
Elements 1, 2, 3 get zone values calculated at their centers.
Elements 4, 5, 6 use properties upscaled from all intersected zones (1, 2, and 3)
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Conductivity Upscaling
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connectionparallelh
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Deformed Mesh 5 layers Semi-Uniform Mesh 10 Layers
Simple Budget Analyzer: Comparing Meshes
2.75% difference
.more in future work
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Future Development
Fully conceptual, simulator-independent approach to building a
groundwater model
Current implementation supports USGS MODFLOW and FEFLOW
FEFLOW: supports 3D mesh design, flow materials, and pumpingwells
Future support for Type 1,2,3 boundary conditions
Additional Analytical models
Additional Finite Difference/Finite Element modelsIntegration with surface water models
Support for Linked simulations using OpenMI technology
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Summary
the classical approach to numerical modeling starts with a grid
or mesh and then assigns model properties and boundariesfor better local modeling the grid is refined over a number of iterations,
which requires you to re-work property zones and boundariesthis can be a time-consuming/frustrating process
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Summary
A conceptual model improves the efficiencies of these iterations,
by housing all data, and providing a visual environmentIt helps with the up-front design of the model; more detailed adjustments
are done on numerical levelIt can be considered as the common root for a family of numerical
models, so it can also be used as a version control for modeling projects
the use of a conceptual model builder allows you to define mesh
and grid-independent model location, flow properties, andboundary conditionsthe model grid/mesh is assigned afterthese have been designed
this allows more flexibility in choosing grid orientation and discretization
grid refinement is easy to apply to conceptual objects
it supports multiple conceptual models for determining the best approach
to simulating a specific groundwater environment
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Acknowledgments
Co-authorsSerguei Chmakov, Petr Sychev, Collin Tu, Marconi Lima,
Schlumberger Water Services
DHI-WASY: Peter Schatzl and Support TeamThe workflow based approach was strongly motivated by
powerful Schlumberger seismic to simulation workflows in the
Petrel software
(http://www.slb.com/content/services/software/geo/petrel/index.asp?)
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References
Anderson, M.P. and W.W. Woessner (1992) Applied Groundwater Modeling: Simulation of Flow
and Advective Transport. Academic Press, Inc. New York.
Visual MODFLOW 3D-Builder Users Manual: Schlumberger Water Services
A New Generation of Waterloo Hydrogeologic Software. MODFLOW and More 2008: Ground
Water and Public Policy - Conference Proceedings, Poeter, Hill, & Zheng -www.mines.edu/igwmc/ pp. 154-158
http://www.twdb.state.tx.us/gam/GAM_GW_model.htm
http://www.ce.utexas.edu/prof/maidment/GISHyd97/gms/gms.htm
http://www.indygov.org/
For more information on the OpenMI project, please refer to the extensive OpenMI website atwww.openmi.org
FEFLOW. FEM File Format
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Thank you
Questions?