Temperatures at the bottom of about half of New Zealand’s 360 abandoned onshore oil and gas wells were hot enough to produce geothermal power, according to GNS Science geothermal scientist Agnes Reyes.
The remaining abandoned wells had enough heat for direct industrial applications and geothermal heat pumps, which operate efficiently at temperatures between 10C and 30C.
Estimated temperatures at the bottom of abandoned wells in New Zealand range from 20C in the shallowest wells to nearly 180C in the deepest wells, some of which are nearly 5km deep.
After compiling an inventory of New Zealand’s abandoned wells, Reyes found the heat within the wells could potentially provide enough electricity to power a city the size of Christchurch (population 350,000).
“The energy available from all abandoned wells in New Zealand with bottom hole temperatures over 80C is about 160 megawatts of electricity,” she said.
“Abandoned oil and gas wells and sedimentary basins have been overlooked as a possible geothermal energy source in New Zealand because they are mostly outside the traditional geothermal areas,” Reyes said.
“France, the US, Australia, Germany, Switzerland and Japan have shown it is feasible to harness geothermal energy from unconventional sources. The technology developed for this purpose is called enhanced geothermal systems or EGS.”
Reyes’ work to date in this area has largely been an add-on to her government-funded research on New Zealand’s low-temperature geothermal systems. These typically have surface springs with temperatures lower than 90C. Most are outside the central North Island’s volcanic zone.
She believes there is so much untapped heat in sedimentary basins and unused wells that it warrants a systematic evaluation to see whether this type of energy production is feasible in New Zealand.
The first step would be to assess the condition of the abandoned wells. Some may be in poor condition and access could be difficult with others. A trial would then enable the engineering, scientific and economic issues to be resolved.
Research such as this would require funding and the support of the oil and gas exploration industry, according to GNS.
Currently, only one abandoned oil well is being used commercially to produce geothermal energy in New Zealand, Reyes said.
The Bonithon-1 well in New Plymouth, drilled in 1908, is a source of thermal water for the Taranaki Mineral Pools.
In Taranaki, however, there are nearly 50 abandoned on-shore wells with bottom temperatures higher than 80C that can potentially be used for binary cycle geothermal power production.
In addition, there are dozens of lower temperature abandoned oil and gas wells in Taranaki where heat can be harnessed directly for uses such as drying of farm produce, milk pasteurisation, greenhouses, and heating houses and offices using geothermal heat pumps.
“Taranaki is an excellent place to start because there are a high number of abandoned wells and it is home to energy-intensive industries such as dairying that would benefit from an extra energy source,” Reyes said.
In other parts of New Zealand, revival of abandoned wells could provide a boost to flagging provincial economies, she said. On the South Island’s West Coast, for instance, there may be potential for commercial spas to be developed at well locations.
Momentum for harnessing this unconventional energy source has been growing steadily in the United States.
US scientists recently estimated the geothermal energy potentially available from unused oil and gas wells in seven southern states was at least 5000MW of electricity.
New wells could be drilled into onshore areas around New Zealand specifically to harness high temperatures at depths of 2500m and below. This could deliver another 800MW of geothermal power, but as drilling wells was expensive, it made sense to explore the possibilities offered by existing wells, she said.
