Power drill

Thermal energy stored in the Earth's crust could be more easily utilised if it were accessed with a new drilling technique that uses superheated steam.

The technology, being trialled this year by its developer Potter Drilling in the US, could help further exploit geothermal energy, which currently supplies less than one per cent of the world's electricity yet has the potential to provide significantly more.

The technique relies on superheated steam to drill through the hard crystalline rocks that contain geothermal wells. The method for generating the superheated steam was developed by Oxford Catalysts, based in the UK.

Dave Wardle, business development director for Instant Steam technology at Oxford Catalysts, said current drilling techniques are laborious and use rotating drill bits to cut through the rock.

'With crystalline rock you wear out the drill bits very fast,' he said. 'This new technology provides a chemical way of cutting rock at reasonably fast speed. There are no moving parts.'

The system works with a catalyst developed by Oxford Catalysts and a special drilling tool designed by Potter Drilling. The Instant Steam catalyst is contained inside the drill head, which is attached to a flexible coiled pipe.

Wardle explained that when peroxide and methanol are piped into the catalyst bed, the catalyst carries out a combustion reaction and produces 800oC steam.

When the steam touches the surfaces of the rock, he said, it causes its crystalline grains to expand. As the grains expand, micro-fractures occur in the rock and small particles — called spalls — are ejected.

Potter Drilling is not the first company to use spallation drilling technology. According to the company, air spallation drilling was used commercially between the 1940s and 1960s for ore mining and was adapted to geothermal drilling by the US Department of Energy in the 1970s.

Yet Potter Drilling's technology, which uses hot steam instead of air to spall rock, can reportedly drill to deeper depths reaching 9,000m.

The company believes this technology could be the key to furthering power generation from geothermal energy, which currently only generates 10,000MW around the world.

Engineered geothermal systems (EGS), which were partly developed by one of Potter Drilling's founders in the 1970s, extract heat from hot rocks in geothermal wells to boil water. The hot water is then used to drive steam turbines that generate electricity.

Potter Drilling claims this is different to other forms of geothermal power because EGS power plants can be developed anywhere that hot impermeable rock exists below ground.

Stuart Haszeldine, an expert from Edinburgh University's School of Geosciences, told The Engineer that many consider geothermal energy a renewable source and electricity produced from it would have a relatively low carbon footprint.

'The carbon cost is the drilling of the hole, but these holes last for many decades,' he said.

While drilling for oil and gas often comes with fears of potential negative impacts on the surrounding environment, Haszeldine said this is not necessarily the case when drilling for geothermal energy.

'Compared to strip-mining coal it is much less environmentally damaging,' he added.

Haszeldine said that electricity produced from geothermal energy plants has the potential to be on a similar cost level to coal-fired power plants.

Wardle said geothermal energy drilling was a ready application for Instant Steam, but there are other ways Oxford Catalysts would like to commercialise its technology.

The company has developed a prototype of a steam-cleaning product that would essentially work like a hot version of Mr Muscle. The prototype uses the same chemical components as the drilling technology to heat up cleaning fluid.

'The kind of product we envision is something that looks like a power cleaner, such as Mr Muscle,' he said. 'You pull it out from underneath the sink, squeeze the trigger and instantaneously you get hot detergent. We're working with partners on developing that product to put it on the shelf.'

Siobhan Wagner