"Walking" anchor and plasma drill promise cheap, deep geothermal power

May 13, 2023

The intense heat under the Earth's surface represents a virtually inexhaustible source of reliable clean energy that would be available 24/7 from anywhere on Earth – you could pull it up as steam to run generator turbines, or pipe it directly into district heating systems.

That's if we could get to it. Earth's most easily accessible geothermal energy is located wherever it's closest to the surface – typically, geologically unstable areas near volcanos and lots of seismic activity, representing only about 3% of the Earth's surface. Otherwise, you can't get to that heat without drilling down through mile upon mile of super-hard rock.

The temperatures and pressures involved in super-deep drilling tend to destroy even the highest-quality drill bits in short order. Changing a bit out means you have to haul the drill head back up from miles underground, put a new one on, then get it right back down the bore before you can start again. This process wastes a lot of time, and time is money when you're hiring these kinds of rigs.

As a result, geothermal energy really only makes a significant contribution to the power grid in places like Iceland, El Salvador, New Zealand and other areas where it's available at shallower depths. Globally, geothermal contributes less than 100 GWh annually to the 166.7 million-odd GWh global energy supply.

Slovakian company GA Drilling was formerly known as Geothermal Anywhere – and that's a perfect encapsulation of the company's goal: to make geothermal heat much cheaper, quicker and easier to access wherever it's needed.

GA has developed two key technologies that work in with existing drilling infrastructure and equipment. The first is a walking anchor system it calls Anchorbit.

The Anchorbit system places two collar sections behind the drill bit, each with extendable pistons capable of pushing out and gripping onto the bore shaft. When the upper collar grips the bore, the lower one extends downward closer to the drill bit, and then it pops out its gripping pistons to allow the upper collar to let go, and slide down to meet it. The process is illustrated in this video:

These anchor collars stabilize the drill bit, preventing the kinds of vibrations you get when operating rotating drill equipment at the end of many miles of cable. They also allow extra weight to be pressed down on the bit. GA says it expects the Anchorbit system should not only double the rate of penetration through tough rock, it'll also double the lifespan of existing drill bits, allowing operators to drill faster for longer, with fewer costly bit changes required.

Anchorbit will accelerate the first 6-odd kilometers (3.7 miles) of drilling, but GA's target depth for geothermal heat is more like 10 km (6.2 miles) underground. To reach this level, the company's second key technology, Plasmabit, will be brought out.

The Plasmabit system can again be connected to a standard drilling rig. But this time, it's a pulse plasma drilling system, which uses a rotating electric arc torch to blast rock with ionized gas at 6,000 °C (10,800 °F) to crack and weaken it, while also blasting it with high-pressure water to mechanically remove chips of rock and send them back up the pipe to the surface. It's basically a long-distance version of the kind of plasma torch tunneling being done closer to the surface by companies like Petra and Earthgrid.

Since it's a no-contact drill bit, there should basically never be a need to pull up and replace the bit. GA says it'll make relatively easy progress though the hard granite down to the 10-km mark, going significantly deeper and cheaper than a normal rig, and cauterizing the bore as it goes. At that depth, you can expect temperatures over 350 °C (662 °F) in most areas, making your bore relevant as a geothermal power plant.

If you want to go much deeper than that, some far more exotic technology is required. MIT spinoff Quaise is attempting to drill to twice that depth using gyrotrons that were originally developed to superheat plasmas in fusion experiments. Getting to 20 km (12.4 miles) deep, says Quaise, would give you temperatures over 500 °C (932 °F), well past the point at which water becomes a supercritical fluid – and power plants using supercritically heated water should be able to extract up to 10 times as much energy from a given volume.

Quaise plans to do this right underneath old coal and gas-fired power stations as they're retired, replacing fossil-fueled heat with clean geothermal, but taking advantage of the existing turbines, grid connections and other infrastructure that would otherwise be stranded when the plants close down.

But this is all dependent on some pretty exotic and cutting-edge technology. The Quaise team is currently "heads down building a couple field demo units in Houston," CEO and co-founder Carlos Araque tells us via email. "Not much to report at the moment but if all goes to plan, we’ll be in the field drilling first holes under the open sky within a year from now."

Meanwhile, GA has just conducted the first "public demonstration" of its Anchorbit system at a Nabors technology center in Houston. We're not sure how public a demonstration of a super-deep drill system can really be, and indeed GA isn't commenting at this point on exactly how deep it went in this demo, or whether it did what it says on the tin in terms of penetration rate and bit lifespan.

"For several years, our team worked relentlessly to enable clean, baseload geothermal power in any place of the world," says GA Drilling CEO and founder Igor Kocis in a press release. "We are thrilled that today we demonstrated in a real well a significant achievement: the successful use of our first Anchorbit tool, applicable to today's geothermal projects. It will improve their returns, reduce the risk, and help the current industry to expand projects into new territories. We are starting a new era for our company and for the whole geothermal sector to become a decisive player in the energy mix. With this breakthrough, we have made another big step toward delivering our promise of 'Geothermal Anywhere.'"

These are some neat technologies, but we're looking forward to seeing how they work in the real world. If GA's drilling advances can truly put cost-competitive geothermal power plants more or less anywhere you want one, this tech could make a huge contribution to global energy production and the race to zero carbon emissions by 2050. And if Quaise hits its targets, the results could be even more significant.

Source: GA Drilling