vancouver, 2006 © 2004 brgm geomodeller – building better models … faster!

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GeoModeller – Building Better Models… Faster!

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Build from data!

• Use classical field data …- geology contacts- dip & strike measurements

• Add data … - build a new model

• Add a fault …- build a new model

• Rather than a model being a once-off final product … it becomes dynamic … and can be updated as required

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Topics

• Challenges

• GeoModeller Software

• The interpolator methodology– Simple layered geology– More complex geology

• Touch on …– Inputs, outputs, geophysics

• Inversion of magnetics & gravity

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Challenge 1: Change

Change a 3D geology model …

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Changing a Geological Model

• We would like to be able to change models … – new data ?– revised ideas ?

• Build the model directly from data ?

Geological Data

Modelled Geological Surfaces

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Challenge 2: Sampling

Sampling the geology signal …

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Houston, we have a problem!

• To communicate an understanding of the geology of an area … I can ‘map’ the area … and produce a geology map ( … I ‘sample’ the ‘geology signal’ !)

? ? ?

? ? ?

? ?

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Houston, we have a problem!

• If I stack up the request like this … and make it a 3D challenge …

… you can see we have a problem …– and it’s a ‘sampling problem’– I do not have a good distribution of samples!

Lots of sampling here

No samples here

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The Solution …

Get the samples … or get smarter!

• Spend lots of money– Drilling … we directly sample the geology

• Use geophysical datasets …– Indirectly sampling the geology signals

• Use all available data in smarter ways …– By integrating geology information– Adding a geologist’s interpretive insights– Using tools that assist the geologist’s task

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Design Goals

• A tool to build a 3D geological model directly from the observed data

… and so the ability to add data … … and build a revised model

• A tool that provides a practical interpretive environment for the geologist … and so makes the geologist’s interpretive skills part of the solution to the under-sampling problem

… able to be used by the field geologist to build a practical 3D model

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GeoModeller in a Workflow Context

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Other Processing …

GeoModeller’s World

Assemble

Tools - Maps - Sections - 3D Models

Database

GISCAD

Tool

- Fluid-flow modelling - Thermal modelling - Earthquake simulation

Presentation

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Other Processing …

Build Model

Assemble

Tools - Maps - Sections - 3D Models

Database

GISCAD

Tool

- Fluid-flow modelling - Thermal modelling - Earthquake simulation

Presentation

GeoModeller

directly from the data

BuildModel

QueryLines

Shapes

Query

Review

Review

Interpret

Interpret

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Build a Model from the Data

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Geology

Stratigraphic Relationships

Field Observations

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Using data … build a Model …

• Stratigraphic succession

• Geology contacts

• Geology dip and strike data

• Faults noted; position and attitude

Goal: Build a 3D geology model …

… directly from the observed data

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Field Observations

Query the Model … predict Geology

• The model is consistent with the observations that have been recorded …

• … but there is scope to improve this model by adding more data.

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Additional field mapping … new data

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Add data … and re-build the model

• Additional geology contact data are now available …– we want to add these observations …– and re-build the model using all data

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Query the re-built Model …

The revised model is better, but there is still scope for further mapping and improvement.

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Further revised geology Model

Further revised model – still based little data – can be used to predict geology beneath cover and into the third dimension.

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The GeoModeller Workbench

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Data-model-query-review-interpret

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A model … but wait, there’s more

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New Data, New Ideas, New Model

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Summarising so far …

• Build a model – directly from raw geology observations

• Actually uses dip and strike data

• I can ‘query the model’ and view it in 2D and 3D views … consider … re-interpret

• I can revise my model as new data, new ideas emerge

• Key Point – I can rapidly test ideas re the 3D structure – see the result of my ideas in a full 3D view. This immediacy of feed-back is critical to the achieving a genuine interpretive environment … to refine or reject my ideas (interpretation)

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GeoModeller’s Interpolator

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Potential Field Method

• We use the mathematics of potentials!– Smoothly curving, sub-parallel layers of geology in 3D space

are analogous to a set of iso-potentials of a scalar (potential) field

Interpolation Method

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More Complex Geology?

Multiple Interpolators

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A more complex example ...

How can I obtain this cross-section using a potential field?

More Complex Geology

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Geological Observations

• Understand the rock relationships … and construct the stratigraphic column

More Complex Geology

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One Field per Series - 1

• Potential of the first series …

Iso-value 1

Iso-value 2

Iso-value 3

More Complex Geology

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One Field per Series - 2

• Potential of the second series …

Iso-value 1

Iso-value 2

More Complex Geology

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One Field per Series - 3

• Potential of the third series …

Iso-value 1

More Complex Geology

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Combine the Three PotentialsMore Complex Geology

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Combine the Potentials - OnLap

ONLAP: Series F2 stops on Series F1

Why ?

More Complex Geology

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Combine the Potentials - Erode

ERODE: Series F2 cuts across Series F1

Why ?

More Complex Geology

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Onlap / Erode Determines the ModelMore Complex Geology

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Purnama, Indonesia

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The Language of Geology

Intuitive working environment

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Geological Intelligence

• Strat. order• Conformable• On-lapping• Erosional• 2D Sections, 3D Viewer• Faults, folds, hinge lines, dip & strike

Use the data a geologist can observe in the field

The lines are not simply lines that satisfy topological rules (GIS), but rather geological intelligence is built into them

Geology

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Faults

• Can be constrained within specified geology series

• Can be finite … with decreasing impact towards the limits

• Can be constrained to stop against specified other faults

Geology

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Limited Faults

N

Geology

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We can define an axial surface … … and create a section-view on that axial surface

… and plot the ‘model’ in that section view of the axial surface …

We could propose that the ‘hinge line’ should be ‘adjusted’ …

Re-compute the model; the fold honours the proposed hinge line.

Fold Axial Surface, Hinge Line We can define an axial surface …

Geology

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Data Inputs

• Your geological understanding of stratigraphic order, conformable packages, their rock relationships …

Plus …• Data from …

– Geo-registered images (then digitise)– Import from GIS, ASCII text files– Import drillhole collars, surveys, geology

Plus …• Your interpretive hypotheses

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Use of Geophysics

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Geophysics as Input

• Geophysics provides a means of ‘sampling at depth’– Advanced geophysical processing technologies can locate

boundaries from which we can deduce geology– We are already exploiting such data via ‘generic’ import

approaches such as ASCII files and image registration– We will expand our ability to directly use such data by

reading a wider range of file formats.

Geophysics

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Geophysics – Forward Model

• Having built a realistic model … and with a knowledge of physical property data - we can compute the geophysical response for gravity, magnetics and any tensor component of either … effectively testing the validity of the model …

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Gas Project – Gravity 1VD vs Gdd

1VD of Bouguer Gravity Airborne Gravity Survey

Target Area

Computed Gdd (Eotvos) 3D GeoModeller Model

0 km 10

Target Area

Geophysics –Forward Model

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Geophysics – Inversion

• The computation of geophysical responses can then taken to the next stage – a geology- constrained joint gravity/magnetic inversion, including any combination of the tensor components of these. Effectively exploring a wide range of possible models that both satisfy geology constraints – and match the observed geophysical signatures.

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Visualisation - Delivery

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• Export 2D to ASCII, GIS• Scaled 2D presentation quality

MapPrint of sections & map

• Export 3D to T-Surf (wireframe)

• Export of web-ready VRML for viewing in Windows Exporer browser (with Blaxxun plug-in)

Delivery

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Conclusions

• GeoModeller assists geologists in rapidly building 3D models, visually reviewing them … and revising them … to make better 3D models

• We have exports for delivering the results to end-user clients

• We can effectively test the validity of our models with geophysical forward and inverse computation of magnetics, gravity and their tensor components

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AcknowledgementsIntrepid Geophysics’ commercialisation of the GeoModeller software has been supported by …

The GeoModeller Consortium – Geoscience Australia, the state Geological Surveys of NSW, Vic, SA, WA, NT & Qld, CSIRO, Geological Survey of Namibia, Barrick Gold (formerly Placer Dome) and Geological Survey of Canada

Australian Government - International Science Linkages This project is proudly supported by International Science

Linkages established under the Australian Government’s innovation statement, Backing Australia's Ability

BRGM – On-going development in several research topics by the R&D group within BRGM

The development work is a team effort by many … but the significant individual contributions of the following is acknowledged: Patrick Ledru, Antonio Guillen, Gabriel Courrioux, Philippe Calcagno, James Parsons, Ray Seikel and Richard Lane.

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