Comparison of Geothermal Structures at Tauhara Geothermal Field, New Zealand and Muara Laboh, Indonesia

Comparison of Geothermal Structures at Tauhara Geothermal Field, New Zealand and Muara Laboh, Indonesia

Comparison of Geothermal Structures at Tauhara Geothermal Field, New Zealand and Muara Laboh, Indonesia A thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in Geology at the University of Canterbury by Joe Struthers 2019 Abstract Understanding the relationships between geological features and hydrothermal fluid pathways is critical for effective geothermal site investigation, exploration and production. Feed zones found within wells indicate fluid conduits. This work demonstrates the development of a workflow using Leapfrog Geothermal modelling software to test which parameters of a given geothermal field influence where these feed zones occur. Two sites were chosen to develop the process: Tauhara, New Zealand, and Muara Laboh, Indonesia. These sites are both situated in extensional environments but have different lithologies, structures and, based on previous studies, are hypothesized to have different geothermal system controls. This research focused on constructing lithology, structure, temperature, and feed zone models to investigate the attributes conventionally understood to influence permeability. The relationships between these were examined using offset distance and combined modelling. Experimentation through iterative reworking was used to improve the efficiency of the workflow. Comparisons were made between the two sites to test the versatility of the interpretive process, and to develop some initial interpretations of the factors controlling feed zones at both sites. The study found that the two sites shared similar structural attributes, both sites are in a transtensional basin, a result of strike-slip and normal faulting processes. Tauhara has permeable lithologies which are subject to caldera collapse structures, particularly at the caldera margins. There is also evidence to show that interaction between the Taupo Volcanic Zone (TVZ) and North Island Shear Belt (NISB) provide key pathways for the circulation of hydrothermal fluids. Muara Laboh has some permeable strata but circulation is more reliant on fracturing proximate to the faulting within the pull-apart basin, with limited areas of hydrothermal circulation. There is still an opportunity to build on this framework, by improving the technical accuracy of the models (for example if more wells are drilled at the sites) and developing additional components in the combined models (for example pressure and alteration). Table of Contents Abstract .......................................................................................................................................................... i Acknowledgements ...................................................................................................................................... ix 1 Introduction .......................................................................................................................................... 1 1.1 Geothermal Systems ..................................................................................................................... 1 1.2 Components of a Geothermal Reservoir ....................................................................................... 3 1.2.1 Geology ................................................................................................................................. 3 1.2.2 Permeability .......................................................................................................................... 5 1.3 Aims and Objectives ...................................................................................................................... 6 1.4 Scientific Merit .............................................................................................................................. 6 2 Study areas ............................................................................................................................................ 8 2.1 Tauhara ......................................................................................................................................... 8 2.1.1 Regional setting ..................................................................................................................... 8 2.1.2 Geology ............................................................................................................................... 11 2.2 Muara Laboh ............................................................................................................................... 17 2.2.1 Regional Setting ................................................................................................................... 17 2.2.2 Geology ............................................................................................................................... 18 3 Methods .............................................................................................................................................. 22 3.1 Leapfrog Geothermal Software ................................................................................................... 22 3.2 Leapfrog Geothermal Model Types ............................................................................................. 23 3.3 Data ........................................................................................................................................... 24 3.4 Input Models ............................................................................................................................... 25 3.5 Geology ....................................................................................................................................... 26 3.6 Temperature ............................................................................................................................... 35 3.7 Feed Zones .................................................................................................................................. 37 3.8 Model Processing ........................................................................................................................ 39 3.8.1 Temperature Isotherm-Isosurfaces ..................................................................................... 39 ii 3.8.2 Distance Evaluation and Fault Offset Isosurfaces ................................................................ 39 3.8.3 Combined Models ............................................................................................................... 41 3.8.4 Block Model ......................................................................................................................... 41 4 Results ................................................................................................................................................. 43 4.1 Geology ....................................................................................................................................... 43 4.1.1 Tauhara ............................................................................................................................... 43 4.1.2 Muara Laboh ....................................................................................................................... 47 4.2 Temperature ............................................................................................................................... 51 4.2.1 Tauhara ............................................................................................................................... 51 4.2.2 Muara Laboh ....................................................................................................................... 53 4.3 Feed Zones .................................................................................................................................. 55 4.3.1 Tauhara ............................................................................................................................... 56 4.3.2 Muara Laboh ....................................................................................................................... 57 4.4 Combined Models ....................................................................................................................... 59 4.4.1 Tauhara ............................................................................................................................... 60 4.4.2 Muara Laboh ....................................................................................................................... 62 4.5 Block Models ............................................................................................................................... 64 4.5.1 Tauhara ............................................................................................................................... 65 4.5.2 Muara Laboh ....................................................................................................................... 65 4.6 Refined Models ........................................................................................................................... 66 4.6.1 Tauhara ............................................................................................................................... 66 4.6.2 Muara Laboh ....................................................................................................................... 69 5 Discussion ...........................................................................................................................................

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