Dec '13/Jan '14

Rock-melting waves

How miners could stop drilling bit by bit

By Pierrick Blin and Antoine Dion-Ortega

To locate a drilling site, simply follow the thick electric cable that meanders out from a large generator. Next to the drill, the sound of high-pitched hammering, which is characteristic of current technologies, has vanished. The only noticeable sounds are the gases whistling through the drill hole and the muted hum of the gyrotron, a vertical tube that sends electromagnetic waves over seven kilometres down in order to melt and vaporize the bedrock. Instead of drill cuttings, at the mouth of the hole, nanoparticles are pulled towards a catchment basin.

This scene could become reality within 10 years, thanks to new drilling technology using directed millimetre waves that is being developed by senior research engineer Paul Woskov of the Plasma Science and Fusion Center at MIT. The idea is to use this technology to meet the most pressing demands in geothermal energy, namely the development of more efficient drilling methods.

A concentrated beam

“The millimetre wave technology I worked with, called a gyrotron, is very similar to a laser beam, except of longer wavelength,” Woskov explains. The use of high-force lasers to focus energy on one point, thus puncturing the bedrock, is not a new concept. It has been widely experimented with but proven impractical for hygienic reasons: Lasers can only operate optimally in environments that are impeccably clean, since their short wavelengths can easily be set off-target by any small particle in their way. Since ejection of secondary particles is inevitable during drilling procedures, any useable technology needs to adapt to this reality.

This is what led Woskov to the idea of using millimetre waves, which are 1,000 times longer than those of lasers. He initiated the first test of his idea in his laboratory at the end of 2008. “When the wavelength is much longer, small particulate scattering decreases significantly and actually almost disappears,” he says. No one had previously considered using millimetre waves for drilling because of their significant natural divergence in open air. “In an open space, millimetre waves act like flashlights, diverging and not covering a long distance,” explains Woskov. “This limitation does not exist in a borehole environment, so they continue to operate just like lasers in a concentrated beam over long distances,” he adds. The waves are also directed through a tube for a certain distance above the drilling surface.

Woskov found that the concentration of millimetre waves into rays makes it possible to heat solid rock at temperatures reaching 3,000 degrees Celsius, transforming it into liquid or even vapour. It is then theoretically possible to drill through any type of rock at a rate similar to that of standard surface drilling – 10 to 15 metres per hour. The main advantages to using waves, though, come as the holes get deeper. “Mechanical drills can drill much faster than 15 metres per hour near the surface, but when you go down to a depth of several kilometres or so, you are lucky to get one or two metres per hour,” Woskov notes. “But a gyrotron that starts drilling at 10 metres per hour should maintain that rate regardless of the depth.”

It would cost between $20 and $25 per metre for a borehole with a diameter of four inches and $100 per metre for a borehole of 10 inches, Woskov estimates. “In one estimate, I assumed a seven-kilometre deep hole, 10 cents per kilowatt hours of electricity, and I came up with a number of $450,000 for the electricity,” he says. Woskov adds the other costs should be relatively similar to the current technology, considering the time saved on drilling.

The art of drilling also involves evacuating drilling residues and strengthening the walls, two steps that have also been completely reinvented by Woskov. The tube that directs the rays, smaller than the hole itself, will be used as a means to introduce a purge gas into the borehole. This will enable rock vapours to cool and break down into ­nanoparticles, as well as to add to the pressure that will evacuate the particles through the space between the rock and the tube.

As the gyrotron works to drill a hole, the walls are simultaneously strengthened. The surface that comes into direct contact with the millimetre wave ray is vaporized, while the peripheral surface, which is subjected to lower energy and temperatures, simply melts or vitrifies. As the ray advances, the walls of the hole are transformed into a layer of glass. This layer could then theoretically be used both to ensure stability and control water infiltration into the hole.

One step at a time

Although laboratory tests have been very promising and have confirmed the potential of such technology, Woskov is aware of the fact that many steps remain before the millimetre wave drilling technique can be commercialized. He estimates that 10 years of research are necessary before applicable technology is developed. “We need to have a pilot-scale demonstration to have some credibility in the community and to ensure that this will really work, because this is very novel and far out right now,” he explains.

Development can be done in stages. “There are many surface applications and shallow applications that might be a first step towards possibly improving the technology for wider things like trenching, mining, tunnelling, and things like that,” says Kenneth Oglesby, president of Impact Technologies, who has seen the potential of this technology and has partnered with Woskov for those first applications. “For these surface applications, it could be something like three to five years of development before commercialization,” he says. For instance, vitrifying hole walls to replace conventional steel casing may well be applied in combination with traditional drilling methods. “More immediately we will be doing some high-pressure tests at Impact on the transmitability of millimetre-waves at pressures typical in current drill hole environments,” he adds.

Use of directed millimetre wave technology in deep drilling is of interest to oil and gas companies and geothermal energy industries, according to Oglesby, but its effectiveness has yet to be proven. However, he says, “When you are looking at such deep applications and early research, it’s more governmental funding at that point. The U.S. Department of Energy has really been good at putting money on the table where industry hasn’t. Impact sees the potential of this technology to change the nature of drilling.”

Woskov is optimistic his technology may see first use in complementary applications to traditional methods. “That may be the initial niche for this to work with established industries,” he notes. “When they get to the point where they are stuck, then bring in the directed beam technology to break through.”

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