A Review of Geological Modeling

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A Review of Geological Modeling
Short Course 503 Three-Dimensional Geologic
Mapping for Groundwater Applications October 27,
2007

• A. Keith Turner
• Colorado School of Mines
• Carl W. Gable
• Los Alamos National Laboratory

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Why Is Modeling Visualization Important?
The World of the Geoscientist Is
Multi-dimensional

• Current interpretation methods limit this view
• Digital versions of traditional maps are not
  sufficient
• Increased efficiency demands computer-based
  methods to
• Integrate and Manage the data
• Interpret geological features
• Visualize attributes spatially and temporally
• Model dynamic Earth processes

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Importance of This Topic

• 3-D subsurface modeling first became feasible in
  late 1980s with the introduction of
  high-performance Unix-based graphical
  workstations
• Developing digital representations of the
  subsurface does not ensure high-quality and
  efficiently managed projects
• Society is increasingly demanding
• multi-scale, multidisciplinary, integrative
  projects
• a shift from passive data collection and
  archiving to dynamic information management and
  dissemination

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Over The Past DecadeEnormously more powerful
computers anddata storage have vastly reduced
costs!

• Continuing, rapid advances in computer HARDWARE
  and SOFTWARE technologies
• Modeling visualization increasingly integrated
• Increasingly realistic models possible

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Problems in Subsurface Investigation are
Unique...

• Subsurface information is often incomplete and
  conflicting
• The subsurface is naturally complex and
  heterogeneous
• Sampling is most often insufficient to resolve
  all uncertainties and
• Scale effects on rock , fluid, and other
  properties are usually unknown.

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Why We Need Special Modeling and Visualization
Tools and Not Just CAD
GEO-OBJECT
ENGINEERING OBJECT
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A Typical Modeling Project
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Geometry (Descriptive) Modeling

• Definition Geometry (Descriptive) Modeling
  involves visually describing, through various
  means such as computer graphics and modeling
  
• The geologic framework
• Distribution and propagation
• of attributes

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3-D Model Involves Two Stages

• Framework Definition
• Borehole and isolated sample data
• Triangulated surfaces
• 2-D grids and meshes
• Iso-volumetric models
• from triangulated surfaces
• from cross-sections
• from grids and meshes
• parametric (NURBS, etc)
• Boundary Representations

• Discretisation and
• Property Distribution
• 3-D grids and meshes
• regular hexahedral
• octree variable
• geocellular
• tetrahedral unstructured
• meshes

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Modeling Often Begins with Borehole Data
(Lynx Geosystems)
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Geometry Models can be Constructed Using
Cross-Sections
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3-D Solid Models can bedeveloped from Multiple
Surfaces
(Lynx Geosystems)
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Layered Models may involve many surfacesComplex
channels and pinch-outs are difficult to model
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Regional (Volumetric) SubdivisionFeasible for
Non-stratigraphic Cases
(C. Gable LANL)
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Framework Models require Grids or Meshes to
assign Property Distributions
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Geological Framework Defined First then Grid
Resolution
(C. Gable LANL)
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Discretisation may involvestructured and
unstructured meshes
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Geocellular Volumetric Model
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Yucca Mountain Represented by a Tetrahedral Mesh
Model
(C. Gable LANL)
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Accurately Modeling Faults is a Challenge

• Near-horizontal thrust faults form additional
  surfaces
• Steeply inclined Faults commonly shown as
  vertical

Edwards Aquifer Model In Texas by USGS
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Advanced Fault Modeling
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Models may be Nestedfrom Regional to Local
Scales
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Purpose of Modeling is Prediction

• Prediction has an extrapolative rather than
  interpolative character
• Involves risk
• Leads to Decision-making

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Predictive Modeling

• Examples
• economic simulations,
• reservoir performance,
• fluid migration and transport models,
• seismic velocity modeling,
• structural restoration

• Definition Predictive Modeling involves
  prediction and/or simulation of events, dynamic
  and other types of processes occurring in the
• geological subsurface
• Solve equations, or other
• numerical analyses
• Forward and inverse
• modeling techniques

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The geologic framework controls the application
modeling
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Contamination plume model shown within geology
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Full contamination plume model
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The Bottom Line Trends in 3-D Modeling

• Continuing, rapid advances in computer
  technologies
• Increasingly realistic models possible
• Coarse- vs. Fine-scale Models
• Cannot easily incorporate geologic knowledge
  (i.e. geologic interpretations)
• Difficulties representing uncertainties
• Hampered by imprecise data and inability to
  adequately sample the prototype

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The Modeling Challenge
How Can We Do Better?

• Build 3-D models from isolated bore data and
  soft information
• Connect known conditions between the boreholes
• Model real-world complexity
• Verify the resulting models
• Represent the uncertainties of the geologic
  framework
• Reduce cost and time of model development

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An Integrated Data Management Process
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What Benefits will an Integrative Approach
Provide??

• To the Individual Scientist
• To the Scientists Organization
• To the Client Organizations and Their Staff
• To Society at Large

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Benefits to the Individual Scientist

• More time for science, so.
• More interactions with colleagues
• More interesting projects/studies
• More job satisfaction
• More publications
• More rapid promotions

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Benefits to the Scientists Organization

• Society
• Maximize Organizations
• Value to Customers
• Maximize Strategic Value BETTER!
• Maximize Financial Value CHEAPER!
• Maximize Operational Effectiveness FASTER!

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Benefits to the Client Organizations and Their
Staff

• Model Consistency
• Data versioning, audit trail, documentation
• QA compliance
• Improved Predictive Capability Model
  Maintenance
• Efficiency streamlining processes, updating
  databases
• Auto-updating decision support tools

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Benefits to Society at Large

• Relevant science that supports decision-making
• Clearly communicated results
• Cost reductions

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Questions???