Proceedings World Geothermal Congress 2015 Melbourne, Australia, 19-25 April 2015 1 An Integrated Approach to 3-D Modelling to Better Understand Geothermal Reservoirs Samantha A. Alcaraz, Isabelle Chambefort, Rose Pearson, Andrew Cantwell GNS Science, Wairakei Research Centre, 114 Karetoto Road, Taupo 3384, New Zealand. s.alcaraz@gns.cri.nz Keywords: Leapfrog Geothermal, 3-D models, Integrated approach, Geological modelling, Hydrothermal alteration modelling ABSTRACT This study presents some tools and techniques to construct an integrated 3-D model of a geothermal field. A synthetic dataset is used to build a model using Leapfrog Geothermal software. The geological setting of the field is defined from surface geological data and borehole information. Hydrothermal alteration mineralogical and chemical zoning is represented in detail, in combination with temperature measurements to characterise particular reservoir conditions. The combination of multiple datasets in one single interface is providing the tools necessary to solve a multidisciplinary challenge and better correlate available information. Fast 3-D interpolation techniques are used to generate geological models and interpolant models. Powerful and flexible visualisation tools facilitate our interpretation of the data and models and identification of possible correlation to improve our understanding of the dynamics and evolution of a geothermal field. This example demonstrates the strength of an integrated approach to help better understand the geological framework and evolution of geothermal reservoir, improves the operator confidence and supports drilling strategies and day-to-day management of the resource. 1. INTRODUCTION Sustainable management of a geothermal reservoir guarantees the longevity and upkeep of the resource for power generation or direct use. It requires a sound understanding of the geological framework of the area, including stratigraphic correlations and structure, alteration signature, as well as the hydrology and evolution of the systems. It presents an interdisciplinary challenge and for a long time, geological, geophysical and reservoir models were created independently, hindering correlations and detrimental to an integrated approach. In recent years, the geothermal industry has been taking advantages of major technical improvements in geoscientific modelling, focussing on moving from traditional 2-D interpretation and visualisation towards the 3-D and even 4-D space, and looking into better data integration to build comprehensive models in an attempt to represent spatially complex and temporally varying geothermal systems. Specifically due to the geothermal reservoir complexity and high costs of collecting data, 3-D modelling software used in the geothermal industry must be capable of handling complex geological geometries and reservoir data from irregularly spaced sparse data sets (Teng and Koike, 2007). Software packages that are intuitive to use, allow 3-D models to be quickly and efficiently built, and routinely updated are most desirable (Cowan et al., 2002). This is generally the case when selecting a software tool, but it is particularly true in the geothermal industry where additional drill holes and surveys will yield additional information which must be used to update the existing models. To address these challenges, a 3-D software package known as Leapfrog Geothermal was developed by New Zealand based software developer ARANZ Geo Limited in collaboration with key players of the New-Zealand geothermal community. Leapfrog Geothermal is specifically designed for our industry and provides a unique interface that allows the integration of geothermal datasets such as geology, structure, temperature, hydrothermal alteration, feed zones, geophysical data and Tough2 numerical models. This field-wide multidisciplinary data is directly visualised, compared and modelled in one single environment (Alcaraz et al., 2010, 2011; Milicich et al., 2010; Massiot et al., 2011; Pearson et al., 2012). This paper presents a case study using synthetic datasets illustrating the tools and techniques available to build an integrated 3-D model of a geothermal field. First we present the methodology followed to build models using Leapfrog Geothermal, and then use commonly available datasets to create a simple geological model which is used as the platform for further data integration. We include temperature data and focus on hydrothermal alteration signature and chemical variations to better understand the properties of the reservoir and its evolution. This model is used as a case study to demonstrate what is achievable using a standard dataset in a geothermal field exploration to production setting. 2. METHODOLOGY Leapfrog Geothermal implements implicit modelling techniques to provide a dynamic solution to solve geological modelling problems. It uses fast 3-D interpolation to derive a continuous function from the data which is evaluated at any point in the model. This is advantageous over a discrete model as the primary data is retained and the model can be re-evaluated at any new resolution from the underlying mathematical function (Cowan et al., 2003). Modelling is automated where possible to decrease processing time and remove hidden biases using an iterative and transparent model building process. 2.1 Data input The sparsity of geothermal datasets means there are multiple interpretations that although consistent with the data have very different scientific implications. Multi-disciplinary data integration is key for modellers to create informed models and test possible solutions. The Leapfrog Geothermal interface facilitates this process by providing tools to highlight the geological relationships