Constructing geologically-constrained 3D models using 3D GeoModeller

Tony Meixner, Richard Lane, Karol Czarnota, Kevin Cassidy

Introduction

The Paterson NGA project is using a number of tools to better understand the time-space evolution of the northwest Paterson Orogen in Western Australia. One of these tools, 3D GeoModeller, is an emerging technology that constructs three-dimensional (3D) volumetric models based on a range of geological information. The Paterson project is using 3D GeoModeller to build geologically-constrained 3D models for the northwest Paterson Orogen. This report documents the model building capability and benefits of 3D GeoModeller and highlights some of the geological insights gained from the model building exercise. The principal benefit of 3D GeoModeller is that it provides geoscientists with a rapid tool for testing multiple working hypotheses.

The Cottesloe Syncline district (Figure 1) was selected as the focus for a trial of the 3D GeoModeller software. The 3D model was built by members of the Paterson Project, as well as model building specialists within Geoscience Australia (GA). The resultant Cottesloe Syncline model, including two dimensional maps and images, was exported from 3D GeoModeller and transformed into a Virtual Reality Modelling Language (VRML), enabling a wide audience to view the model using readily available software. The VRML model requires the free Blaxxun Contact 5 plug-in to be downloaded and installed.

Figure 1. Scanned image of the Broadhurst 1:100 000 geological map sheet (Bagas, 2004). The black outline shows the 3D model area (30 × 35 km).
Rudall Complex - pink
Coolbro Sandstone - tan
Broadhurst Formation - brown
Paterson Formation - blue
[view full size - JPG 308 KB]

3D GeoModeller introduction

3D GeoModeller is a software tool for constructing 3D geological models. Geological boundaries within the models are defined by implicit mathematical functions that take into account the lithological contacts and orientation measurements supplied by the user. An integrated feature of the program is the ability to test and modify these models using potential field (magnetic and gravity) inversion once physical properties have been assigned to geological units.

3D GeoModeller (previously called 3DWEG) was originally developed by Bureau de recherches géologiques et minières, France (BGRM) as part of GeoFrance 3D. Geoscience Australia is a member of a consortium that includes Intrepid Geophysics, BRGM, all of the Australian State and Territory geoscience agencies, CSIRO, as well as other overseas government and commercial organisations. The purpose of the consortium is to foster development of 3D GeoModeller into a robust and versatile software package. Intrepid Geophysics is commercialising the software, and version 1.0 was released in late 2005.

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Construction of 3D models

3D GeoModeller constructs models based on geological principles, geological observations and inferred information. The models are based on the following information:

• A stratigraphic pile with the geological units related by conformable, onlapping or erosional contacts,
• Geological contact points,
• Geological orientation data (i.e., strike and dip measurements), and,
• Faults.

The geological observations can be input in map view, section view, as drillhole information or as completely general 3D points. Following computation of the mathematical functions that define the boundaries of units within a 3D model, the results can be rendered and viewed in 2D as maps and sections or as a 3D model in 3D GeoModeller. Shapes (triangulated surfaces) can be built for each geological unit and exported in GoCad T-Surf format allowing for the import and visualisation in 3D packages such as GoCad and FracSIS. VRML files can be generated for visualisation in a web-browser. Voxel mesh (voxets) versions of the 3D geology model can also be created for visualisation or as an input to geologically constrained gravity and magnetic inversion or other volumetric application.

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