PROCEEDINGS, Thirty-Sixth Workshop on Geothermal Reservoir Engineering Stanford University, Stanford, California, January 31 - February 2, 2011 SGP-TR-191 3D GEOLOGICAL MODELLING USING NEW LEAPFROG GEOTHERMAL SOFTWARE S. Alcaraz 1 , R. Lane 2 , K. Spragg 2 , S. Milicich 1,3 , F. Sepulveda 4 and G. Bignall 1 1 GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand. s.alcaraz@gns.cri.nz; s.milicich@gns.cri.nz; g.bignall@gns.cri.nz 2 Applied Research Associates Ltd. (ARANZ), P.O.Box 3894 Christchurch 8140, New Zealand. r.lane@aranz.com; k.spragg@aranz.com 3 School of Geography, Environment and Earth Sciences, Victoria University, Wellington, New Zealand. 4 Contact Energy Limited, Wairakei Power Station, Private Bag 2001, Taupo 3352, New Zealand Fabian.Sepulveda@contactenergy.co.nz ABSTRACT Leapfrog Geothermal is an innovative 3-D modelling visualisation software and resource management tool, developed by ARANZ Geo (Applied Research Associates Ltd), with geoscientific input from GNS Science, to meet the 3-D computing needs of the geothermal industry. Leapfrog Geothermal is based on implicit modelling methods that represent geology, structure, geophysical and reservoir data with fitted mathematical functions. Complex geological models are built by combining measured field data, specialist interpretation and user editing. The advantage over conventional grid based systems is one of flexibility and speed, with a model that can be used to populate grids with a range of parameters, depending on user purpose. Hydrothermal alteration, geophysical data, temperature and other reservoir data are modelled as transition surfaces and/or numerical models, and can be combined with rock property and well feed zone data to refine the hydrological structure of a geothermal system. Downhole logging data (e.g. BHTV images) can be integrated to help define fault geometries, lithological discontinuities, and fracture network patterns. The resultant geological model consists of closed unit boundaries that help establish structural and rheological controls on fluid flow (i.e. permeability structure) in the geothermal system. A tool for drillhole design and well targeting has recently been added to Leapfrog Geothermal. Current development focuses on integration of output data from numerical reservoir simulation (e.g. Tough2, Feflow) software at the resolution and scale required to visualise the past and predicted response of the system to development, and aid resources management. Leapfrog Geothermal is already used by developers at geothermal fields in the Taupo Volcanic Zone (New Zealand), as it can rapidly build user-friendly models, assist drilling engineers and geoscientists in their day to day activities, and provide insights that support long-term, strategic field management decisions. BACKGROUND In the last few years, exploration, production and injection drilling have provided new information on the geology and structure of several geothermal fields in the Taupo Volcanic Zone, New Zealand (Figure. 1). Consequently, geological insights from deep drilling at Wairakei-Tauhara (Rosenberg et al., 2009, Bignall et al., 2010), Ohaaki (Milicich et al., 2008), Kawerau (Milicich et al., 2010a) have been used in combination with 3-D Leapfrog Geothermal modelling software to develop visualisation models of the geothermal fields. This paper describes Leapfrog Geothermal software, its development, and how it is being used to assist well targeting, and enhance our geological understanding of the fields. From November 2005 to July 2007, ten production and two injection wells were drilled by Contact Energy Ltd. in the Ohaaki Geothermal Field (~20 km NE of Taupo), in areas where few wells had previously penetrated below -1000 m.a.s.l.. Whilst new information was obtained on the stratigraphy and basement structure, relationships between some geological units were difficult to resolve. This prompted GNS Science (GNS), in partnership with Applied Research Associates Ltd. (ARANZ) to develop a new 3D modelling tool, Earth Research, which extended the functionality of the mining industry software Leapfrog™ (Cowan et al., 2004) to aid geological interpretation, by adding specific geothermal tools and applications.