Old oil wells tipped to be geothermal power source

The revival of abandoned wells could boost flagging provincial economies. File picture

Abandoned oil wells could generate enough electricity to power a city the size of Christchurch, according to a study from Crown research institute GNS Science.

Temperatures at the bottom of about half of New Zealand's 360 abandoned on-shore oil and gas wells are above the critical 80C needed to produce geothermal power, says scientist Agnes Reyes.

The rest had enough heat for direct industrial applications and geothermal heat pumps.

After compiling an inventory of abandoned wells, Reyes realised the heat could be harnessed to potentially provide as much as 160MW of electricity.

"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 United States, Australia, Germany, Switzerland and Japan have shown it is feasible to harness geothermal energy from unconventional sources."

Reyes believes there is so much untapped heat in sedimentary basins and unused wells that it warrants a systematic evaluation to see if 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 an issue with others. A trial would then enable the engineering, scientific and economic issues to be resolved.

Taranaki would be the obvious place to start because it has many abandoned wells and is home to energy intensive industries such as dairying that would benefit from an extra energy source.

The region has 50 abandoned on-shore wells with bottom temperatures higher than the 80C needed.

In other parts of the country, revival of abandoned wells could provide a boost to flagging provincial economies.

On the West Coast, for instance, there may be potential for com-mercial spas to be developed at well locations.

Already the Bonithon-1 well in New Plymouth, drilled in 1908, is a source of thermal water for the Taranaki Mineral Pools.

Estimated temperatures at the bottom of abandoned wells range from 20C in the shallowest to nearly 180C in the deepest wells, some of which are nearly 5km deep.

Momentum for harnessing this unconventional energy source has been growing steadily in the US.

Scientists there have estimated the geothermal energy potentially available from unused oil and gas wells in Alabama, Arkansas, Florida, Louisiana, Mississippi, Oklahoma and Texas was at least 5GW of electricity.

Reyes says abandoned oil and gas wells are not the only potential new energy source.

New wells could be drilled into on-shore areas to harness high temperatures at depths of 2500m and below. This could deliver another 800MW of geothermal power.

"New technology means that much of New Zealand's subsurface has become one big geothermal source.

"As drilling wells is expensive, it makes sense to explore the possibilities offered by existing wells."