University of Otago Geology Seminar

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 2-3 km 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% 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.

Cécile will be presenting the seminar remotely (https://bit.ly/otagogeology); however, we will also set-up the Benson Common Room (Gn9, Geology Building) for those of you who would like to join us for the talk in person.

Contact: jack.williams@otago.ac.nz