Potter Drilling, which is partly funded by Google.org, is developing a novel drill which uses heat, rather than abrasion, to break through rock.
Rocks do not expand uniformly when they get hot. This creates stress between the grains of the mineral sand that causes them to break apart. According to Jared Potter, chief executive of Potter Drilling, “The key is to heat it very quickly”.
The idea was developed in the 1950s using hot air, effectively fired from a jet engine, to split rocks. But this only worked close to the surface in applications such as quarrying. The Potter drill uses super-heated water rather than air and is expected to work at great depths.
In a traditional drilling rig, most of the energy is wasted in friction and other inefficiencies. Drill bits wear out frequently – in certain types of rock, it may only be possible to drill for 30 metres before they need to be replaced. Jared Potter explained that “Our technology doesn’t have a bit, can drill continuously and we can drill 3-5 times faster than they can. .. And we’re not taking the bit in and out of the hole. Our energy is right at the rock face.”
In the past 18 months, the company has drilled test holes of 2.5 to 10 centimetres in diameter through hard rocks. In August this year, the company will, for the first time, drill a 10 centimetre hole to a depth of 300 metres. Jared Potter said that “A realistic target for this type of intermediate development would be 5 kilometres. Eventually our goal is to be able to drill to 10km.”
The Massachusetts Institute of Technology has estimated that tapping just 2% of the potential of enhanced geothermal (“hot rock”) energy between 3 and 10 kilometres below the surface of the continental USA could supply more than 2,500 times the country’s total annual energy use.