Geology Department seminar: Fractures and fluid flow through naturally fractured geothermal reservoirs, Taupō Volcanic Zone, New Zealand
Characterising the fracture networks and their contributions to permeability is an important component to sustainably use geothermal energy, and to understand rifting processes. Fractures directly observed in 2–3km deep geothermal borehole images of the Taupō Volcanic Zone are fantastic datasets to unravel links between fractures and permeability.
Borehole images were acquired during the 2019–2021 drilling campaign for the new geothermal power station at Tauhara by Contact Energy, which will generate 3 per cent of New Zealand’s electricity from late 2023. Fracture orientations are consistent with the Taupō Rift with local variations. Permeable zones are associated with reservoir-scale faults, fracture clusters or series of fractures. However, similar fracture characteristics are also found outside permeable zones. Modelling of flow through discrete fractured networks (DFN) that uses interpretations of borehole image from the Wairakei and Rotokawa geothermal fields shows that the fracture networks are connected are reservoir scale, even though over half of the fractures are not connected. Fluid particles can take numerous pathways, with similar behaviour to real tracer tests. The pressure distributions in individual DFN realisations are variable but mean flows and permeability anisotropies derived from multiple realisations can be used in traditional continuum models at a limited computational cost.
This talk summarises two very recent papers: Massiot, C. et al. (presented at the World Geothermal Congress September 2023); and Kissling, W.M. and Massiot, C. (2023, Geothermal Energy).
About the speaker
Dr Cécile Massiot (GNS Science) is a structural geologist and borehole measurement specialist who aims to unravel characteristics of fracture systems which conduct fluid flow in the Earth's crust to improve resource management and understanding of tectonics. She expands borehole data with outcrops, fracture models and geophysical surveys. She contributes to borehole data interpretation in the Deep Fault Drilling Program (Alpine Fault, New Zealand, 2014); and IODP Exp. 376 “Brothers Arc Flux” (Kermadec arc offshore New Zealand, 2018). She is the lead proponent of the CALDERA scientific drilling concept aiming to unravel the interactions between an active caldera, rift, fluid and deep biosphere at the Okataina Volcanic Centre.
Zoom
This seminar will be livestreamed via Zoom at the link below:
