Two wells for the price of one

 By Robin Wylie

Oil wells could soon be providing an unlikely source of renewable energy. The hot water that is removed during the hydrocarbon drilling process could provide a large, untapped source of geothermal energy, according to studies. If the geothermal potential of oil wells can be tapped, it offers a clean – and importantly, cheap – source of renewable energy. The cost of exploration and drilling is the main barrier to geothermal power. Since oil wells have already been drilled, this cost is removed completely…

Geothermal heat is one of the most promising forms of renewable energy our planet has to offer. The International Energy Agency estimates that by 2050, geothermal energy could contribute 1400 trillion watt-hours of power each year – seven percent of the world’s current energy consumption. And the hydrocarbon industry could play a surprising role in this development.

Statistically speaking, oil wells are badly named. The main liquid they produce isn’t black, but blue. Water makes up as much as 98% of the fluid that comes out of an oil well. In the past, this “water-cut” was considered a nuisance by drilling companies, but it could soon be powering homes.

The water pumped out of oil wells can reach temperatures of 100°C (212°F) or more, due to the natural geothermal heat found at such depths. This hot water can be used to produce electricity in much the same way as conventional geothermal fluids are used in places like Iceland. Geothermal water derived from oil wells isn’t as hot as other kinds, but it does come with a major advantage — its price.

A recent study found that in Qatar, oil wells could be converted into geothermal plants (while still producing oil) with an output of 5MW. What's more, the price of the electricity would be extremely competitive, at 6 US cents/kWH, meaning that the plants could pay for themselves within five years

One of the main barriers to the expansion of geothermal energy is the cost of drilling down to tap the hot fluid. Forty percent of the price of a geothermal plant goes into making the well. By using existing oil wells, this expense could be cut out entirely, potentially making it much easier to implement geothermal energy generation on a wider scale.

Geothermal energy harvesting using oil wells is still at the test stage. But new research suggests that it could eventually offer a new, economically viable source of renewable energy. A recent study in the journal Energy found that an oil well in Qatar could theoretically sustain a five megawatt geothermal power plant, at just ⅔ the operating cost of an equivalent gas-fired power station.

As well as a price cut, using oil wells to gather geothermal energy could significantly increase the energy source’s global output. If all the waste water from hydrocarbon drilling in the US could be harnessed, it would generate approximately 12 trillion watt-hours of power per year. This would boost the global output of geothermal electricity by almost 20% (it currently stands at 67.2 TWh). If the same could be done globally, that number could double. It might be naive to imagine that the necessary modifications to infrastructure could be made on such a scale – but where there’s a well, there’s a way.

about the author
Robin Wylie
Freelance earth/space science journalist. Currently finishing off a PhD in volcanology at University College London.