INTRODUCTION
One of the major impediments to the successful development of Australia's geothermal energy resources is uncertainty in the temperature distribution in the crust. While there are many temperature measurements from wells available in Australia (e.g. OzTemp, 2010) , they are unevenly distributed across the continent. Surface heat flow data is one of the most valuable datasets available for predicting temperature at depth; however acquisition of surface heat flow data is time consuming although affordable in comparison to directly drilling to reservoir depths. To overcome the lack of well and surface heat flow measurements, thermal modelling applied to 3D geological maps is a means of predicting temperature distribution between and beneath measurement points.
INTRODUCTION
Underworld is a 3D geodynamic modelling framework capable of deriving viscous or viscoplastic thermal, chemical and thermo-chemical models consistent with tectonic processes, such as mantle convection and lithospheric deformation, over long time scales (http://underworldproject.org/; Quenette and Moresi, 2010) . Underworld is parallelised which means that individual simulations can be run on multiple processors. It is also open source which means that it is freely available to users. One of Underworld's capabilities is 3D modelling of the temperature distribution based on a 3D map of thermal properties. Despite its scalability and the fact that it is open-source, the uptake of Underworld to date has been limited by the fact that it is not easily usable by non-specialists. In particular, the process of creating and running an Underworld input file is not straightforward.
INTRODUCTION
The process of defining the 3D distribution of thermal properties for modelling in Underworld can be facilitated through the use of geological modelling software, such as Gocad (http://www.pdgm.com/products/gocad.aspx). Gocad allows the integration a variety of distinct geoscience datasets to construct a 3D geology map which can then be attributed
SUMMARY
The Virtual Geophysics Laboratory (VGL) is an environment that was developed as a data discovery and delivery facility, incorporating software and computing facilities. This design enables geoscientists to store, discover, retrieve and process datasets. Recent developments are expanding the VGL to incorporate the functionality of the Underworld software. Underworld is open source, parallelised software capable of calculating the 3D temperature distribution in the crust.
SUMMARY
Numerical modelling of temperature is a tool that can be used to predict the temperature distribution at depth between and beneath measurement points based on a 3D geological map. Due to their size, temperature simulations performed on some of these 3D maps can have large memory requirements. To address these requirements and reduce computation time, cluster computing facilities (which have multiple individual processors) can be utilised. In order to analyse uncertainty quantitatively, hundreds to thousands of individual runs are often needed and therefore cluster computing facilities are necessary to complete the runs in a reasonable timeframe.
SUMMARY
The new developments to VGL will facilitate the discovery and access to 3D geological maps. They will also provide easier access to the Underworld software, and will provide the high performance computing facilities (hosted at the National Computational Infrastructure and elsewhere) required to run large models. The metadata associated with each run performed using VGL is automatically stored, and therefore runs completed on VGL will be repeatable and testable.
SUMMARY
Key words: geothermal, modelling, computing with thermal properties for numerical analysis in Underworld or other software.
SUMMARY
The regional scale 3D geological maps on which temperature simulations are conducted can contain up to tens of millions of cells (e.g. Meixner et al., 2012) . Conducting temperature simulations on these 3D maps at full resolution can require considerable memory. The memory required often exceeds that available on standard desktop machines. Even when there is sufficient memory for simulations to successfully run, the time taken for simulations to run (hours to days) is often prohibitive. Therefore to perform the simulations at full resolution in a reasonable timeframe it is necessary to access either a high performance desktop machine with a powerful processor or cluster computing facilities with multiple processors. Without access to these facilities it is often necessary to compromise on either model resolution or computation time, or both. Furthermore, access to cluster computing facilities allows uncertainty to be numerically analysed through running an ensemble of hundreds to thousands of models with a range of input parameters (e.g., Meixner et al, 2012; Haynes, 2012) .
SUMMARY
As part of a National eResearch Collaboration Tools and Resources (NeCTAR; http://nectar.org.au) funded project, Geoscience Australia is working with Monash University and CSIRO to develop tools to streamline the process of importing a 3D map into Underworld, running a model and exporting the results for analysis and visualisation. The project integrates Underworld into the Virtual Geophysics Laboratory (VGL), an environment which enables geoscientists to store, discover, retrieve and process datasets. The goals of the project are:
SUMMARY
1. With Monash University, develop code that allows Gocad format 3D maps to be imported to Underworld; and 2. Incorporate the 3D geological maps, and Underworld, into VGL to provide an interface for both discovering and selecting 3D maps, and importing and running them in Underworld.
UNDERWORLD SIMULATION WORKFLOW
The process of translating a 3D geological map to an Underworld thermal model can be summarised as follows:
UNDERWORLD SIMULATION WORKFLOW
1. Generate an Underworld mesh of desired resolution; 2. Assign thermal rock properties (thermal conductivity and heat production) to every cell in the mesh. 3. Assign boundary conditions for the simulation; and 4. Run the model. These steps can be time consuming and difficult for the nonspecialist who is unfamiliar with the Underworld code and input file format. To address this issue, a Gocad Toolbox has been produced, which organises the conversion from Gocad to Underworld, allowing models to be run quickly and easily. Simulation parameters such as model boundary conditions and number of processors are specified by the user when running the model. To run, the toolbox requires a Gocad voxet that defines the distribution of each geological unit in the model, and a csv file containing thermal rock property information for each geological unit. This script has been integrated into the VGL workflow for easy access by users.
VIRTUAL GEOPHYSICS LABORATORY
The Virtual Geophysics Laboratory is available at http://vgl.auscope.org/. Formerly called the Virtual Exploration Geophysics Laboratory (VEGL; Chopping et al. 2012) , VGL was developed on top of an existing data discovery and delivery portal (http://portal.auscope.org/) developed within AuScope. The aim of VGL is to facilitate data discovery and delivery, and to facilitate access to software and compute facilities. VGL currently provides access to publicly available gravity, magnetic and radiometric datasets and is being expanded to incorporate 3D geological maps. For numerical analysis, VGL currently supports the University of British Columbia -Geophysical Inversion Facility (UBC-GIF) software for Gravity and Magnetic inversions (Li and Oldenburg, 1996; Li and Oldenburg, 1998) , and Escript (https://launchpad.net/escript-finley), a Pythonbased programming tool for numerical modelling using the finite element method. It is being expanded to incorporate Underworld. The compute facilities currently available in VGL include the National Computational Infructure (NCI) cloud facility in Canberra, and the NeCTAR cloud in Melbourne.
VIRTUAL GEOPHYSICS LABORATORY
There are four stages to using Underworld within VGL:
VIRTUAL GEOPHYSICS LABORATORY
1. Discovery and selection of 3D map; 2. Sign in and job construction; 3. Job submission and monitoring; and 4. Job registration.
VIRTUAL GEOPHYSICS LABORATORY
The first stage is to select a 3D map. This can be achieved by capturing from the VGL home page, or at a later stage by uploading from the local disk. Three files are captured: a 3D geological map in Gocad voxet format (consisting of two individual files), and a csv file, which provides thermal rock property values for each geological unit in the 3D map. The csv file consists of four columns: geological unit name, unit number, thermal conductivity and heat production.
VIRTUAL GEOPHYSICS LABORATORY
The second stage requires sign in using an ID provider such as www.myopenid.com. Once sign-in has been completed, a job can be constructed. First, a new job is created, and then files are added to it, sourced either from the portal or locally. These files include the input files described above, and can also include additional job run scripts if these are desired. Finally, run parameters and boundary conditions are entered and used to automatically generate a job script to run Underworld.
VIRTUAL GEOPHYSICS LABORATORY
The job is then submitted, and can be monitored as it runs. Once the job has completed, files can be viewed and if desired, downloaded. For Underworld, the outputs are provided in various light text and hdf5 formats, which can be visualised in software such as Paraview or VisIt. Alternatively the hdf5 files can be used directly for analysis in Matlab or in Python via PyTables.
VIRTUAL GEOPHYSICS LABORATORY
Finally, all job parameters are automatically captured during the run, allowing the user to easily identify what has been run. This metadata, including the job script used to run the job, can optionally be registered to Geonetwork: http://geonetworkopensource.org/. rd International Geophysical Conference and Exhibition, 11-14 August 2013 -Melbourne, Australia 3
CONCLUSIONS
The incorporation of the open source geodynamic modelling software Underworld into VGL will have many benefits. Firstly it will provide a platform to bring together and facilitate access to 3D geological maps developed for various purposes. Secondly, it will provide researchers easier access to thermal modelling software: users will no longer require detailed knowledge of the Underworld code and input formats. Thirdly, it will allow users to have access to high performance compute and cloud computing facilities. This will mean that the amount of time required to run an Underworld simulation will be reduced. The automation of the mesh generation and model setup procedures will also reduce the amount of time required to prepare jobs. Finally, because all job parameters are automatically captured during the run, any work done on the VGL portal is repeatable and can be tested.

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