Abandoned Wells An Untapped Energy Source

12 April 2006

Abandoned Wells An Untapped Energy Source - Scientist

New Zealand could potentially harness up to 160 megawatts of electricity by tapping in to the geothermal properties of abandoned oil and gas wells, a scientist says.

Temperatures at the bottom of about half of New Zealand’s 360 abandoned on-shore oil and gas wells are hot enough to produce geothermal power, says geothermal scientist Agnes Reyes of GNS Science.

And the rest had enough heat for direct industrial applications and geothermal heat pumps, which operate efficiently at temperatures between 10degC and 30degC.

After compiling an inventory of New Zealand’s abandoned wells, Dr Reyes realised the heat within the wells could potentially provide enough electricity to power a city the size of Christchurch.

“ 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,” Dr Reyes said.

“ France, the United States, 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.”

Her 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 90degC. Most are outside the central North Island’s volcanic zone.

Dr 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.

Research such as this would require funding and the support of the oil and gas exploration industry.

“ An encouraging factor is that engineering and geological issues that are traditionally seen as barriers to geothermal development can be overcome by the technology of Enhanced Geothermal Systems.”

There is presently only one oil and gas well being used commercially to produce geothermal energy in New Zealand, Dr 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 there are nearly 50 abandoned on-shore wells with bottom temperatures higher than 80degC. This means they could 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 could 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.”

In other parts of New Zealand, revival of abandoned wells could provide a boost to flagging provincial economies. On the South Island’s West Coast, for instance, there may be potential for commercial spas to be developed at well locations.

The oil and gas industry views with dismay the way water can sometimes overwhelm a hydrocarbon reservoir. However, the geothermal industry views this natural phenomenon as an opportunity to harness a different form of energy – geothermal.

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

“ The energy available from all abandoned wells in New Zealand with bottom hole temperatures over 80degC is about 160 megawatts of electricity. This would be enough to power a city the size of Christchurch.”

Momentum for harnessing this unconventional energy source has been growing steadily in the United States. Recently scientists in the US estimated the geothermal energy potentially available from unused oil and gas wells in Alabama, Arkansas, Florida, Louisiana, Mississippi, Oklahoma, and Texas was at least 5000MW of electricity.

Abandoned oil and gas wells are not the only potential new energy source. New wells could be drilled into on-shore areas around New Zealand to harness high temperatures at depths of 2500m and below. This could deliver another 800 megawatts of geothermal power for New Zealand, Dr Reyes says.

“ 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.”

ENDS

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