Dr Cécile Massiot

Research by an international student who earned her PhD at Victoria University of Wellington has improved our understanding of how hot fluids flow through fractured rocks underground, and will thus help in the development of geothermal energy.

The study by Cécile Massiot, who graduated in May 2017 with a PhD in Geophysics, focused on determining the nature of the fractures – cracks in the rock – that control the circulation of fluids in the Earth’s crust. “There are myriads of fractures underground, but a common challenge in geosciences is mapping where they are, how big they are, and which ones actually serve as pathways for fluids,” said Dr Massiot.

She added, “Identifying the characteristics of those fractures that guide fluids is critical for the exploration and management of geothermal renewable resources, which currently accounts for nearly a quarter of New Zealand’s electricity supply.”

Dr Massiot compared observations made at the surface of the Earth where fracture systems can be seen and touched, with measurements from boreholes where data is sparse, but directly representative of underground conditions. Part of her study focused on the fracturing adjacent to the Alpine Fault on the West Coast of New Zealand’s South Island, where scientists drilled nearly 900 metres deep to measure subsurface conditions.

The project, led by Victoria University’s Professor Rupert Sutherland, involved more than 100 scientists from 12 countries, including Dr Massiot. The results of the project, published in Nature, reveal surprisingly high temperatures next to the Alpine Fault and the potential for large geothermal resources in the area. Scientists found discovered water at a depth of 630 metres that was hot enough to boil. Similar geothermal temperatures are normally found at depths greater than 3 km.

“Determining the layout of fractures near the Alpine Fault is key to understanding the role fluids play in earthquake processes,” said Dr Massiot. The Alpine Fault is known to have magnitude 8 earthquakes roughly every 300 years.Dr Massiot added, “The high temperatures found in the borehole also open new opportunities for exploring geothermal resources.”

The Alpine Fault on New Zealand's South Island (image by Pseudopanax, used under CC license)

Dr Massiot, who is originally from France, earned her MSc in Geosciences from the Institut National Polytechnique de Lorraine and engineering diploma in Petroleum Geosciences and Reservoir Engineering from the Ecole Nationale Superieure de Geologie in France in 2010. She went to New Zealand in the same year to work at GNS Science, an autonomous research institute established by the government. Her thesis supervisors were Professor John Townend, who heads Victoria University’s school of earth sciences, Professor Andrew Nicol, formerly with GNS Science and now at the University of Canterbury, and Dr David McNamara, formerly at GNS Science and now at the National University of Ireland, Galway.

“My results show that the original fracture networks that formed within lava as it cooled at the Earth’s surface millions of years ago, now also control the architecture of fracture systems steering geothermal fluids,” said Dr Massiot. “These findings will improve the use of geothermal resources in New Zealand and overseas, and help us to better understand pressure and temperature conditions in conventional geothermal settings such as those near Taupo, and unconventional geothermal settings such as the Alpine Fault.”

Dr Massiot is now back at GNS Science, and will continue to do research in partnership with geothermal operators who have shown strong interest in incorporating the new data into their models. This will help improve the operating efficiency of geothermal power stations.

The research was funded by GNS Science via the Sarah Beanland Memorial Scholarship, and made use of data provided by the Rotokawa Joint Venture and Mercury New Zealand. Dr Massiot's thesis can be viewed here.

Founded in 1897, Victoria University is among the top 150 universities in the world for earth and marine sciences in the 2016-17 QS World University Rankings. Its 21,000 students and more than 2,500 staff are spread across three campuses in Wellington, the capital of New Zealand. The QS Rankings website notes that Victoria University is not only the number one ranked university in New Zealand for research quality, but also has the advantage of being located in the national capital, ensuring strong links with government departments and agencies, international agencies, industries, environmental organisations, and some of New Zealand’s major research institutes.

Victoria University of Wellington (photo by Denisbin, used under CC license)