A New Zealand fault springs geothermal surprise on earthquake researchers

Geothermal energy could be used for agriculture, industry and tourism, says team member Doug Schmitt

Suzette Chan - 17 May 2017

Scientists drilling into a New Zealand fault line unexpectedly found very high temperatures underground, and with them, a potential source for geothermal energy.

The researchers were hoping to learn more about the forces in the earth leading to earthquakes. To do this, they drilled a very deep borehole into the Alpine Fault, major plate boundary fault that runs most of the length of New Zealand's South Island and separates the Pacific from the Australian plates. The fault produces large earthquakes approximately every 300 years, and it last ruptured in 1717.

At the depth of 630 metres, the project team discovered water that was hot enough to boil. Similar geothermal temperatures are normally found at depths greater than 3,000 metres or more.

"We were all quite surprised by this," says University of Alberta geophysics professor Doug Schmitt, a member of the Deep Fault Drilling Project led by New Zealand geoscientists and including over 40 international scientists. "I had thought that because of the huge precipitation there [9 m per year] that ground water circulation would have keep the temperatures low at the depths we were working at, so the rapid rise in temperature was unexpected."

Schmitt and graduate student Deirdre Mallyon, who was co-supervised by associate professor Claire Currie, were both on site for the duration of the drilling, which took place in 2014 from late October to late December. They faced natural and technological challenges.

"Deirdre took some of the hard jobs and did the night shift making measurements of water levels and drilling fluid density," says Schmitt. "Sometimes this was not easy as she had to contend with essentially horizontal downpours due to strong winds." (Mallyon went on to complete her MSc and is now working in the environmental sensing and monitoring industry.)

Meanwhile, Schmitt's plans to set up permeability and stress measurements in the borehole were scuppered by a number of factors. "There were problems with a cable that broke and dropped a large piece of steel into the borehole in the early stages of the drilling; it took weeks to 'fish' it out," he recalls. "Then the borehole began to deviate strongly in the strongly textured rocks. Finally, there were casing issues that led to the end of the drilling before we were able to reach the fault proper."

After the results of the heat measurements came back, collaboration scientists recognized the potential for industry and tourism.

"The heat can be used for many purposes, from greenhouses to fish-farming," Schmitt says. "The area in New Zealand actually has a very large dairy industry and that certainly requires lots of hot water. With regards to energy production, one can use the heat directly for a variety of purposes but one still would need higher temperatures-so go deeper-to be able to effectively generate electricity. With regards to tourism, this heat obviously can be used for thermal spas. The West Coast of the South Island is a heavy tourism zone, so there should be lots of potential for this."

Schmitt says that Alberta could also benefit from geothermal activity, but not in the same way. "We have no major plate bounding faults in Alberta for example. We do have potential in areas near the Rocky Mountains that have relatively high temperatures at depths that are likely economically practical for electricity generation especially given the high cost of transmission in Alberta. We also have the potential for use of geothermal heat from various formations in the sedimentary basin that could be used in a wide variety of industriesr municipalities particularly if heat pump technologies are used."

The findings of the Deep Fault Drilling Project were published in the science journal Nature today.